What Does a Hognose and an Amaryllis Have in Common?

David Zaff

Science and Operations Officer NOAA/ National Weather Service Buffalo NY

Each year, the National Weather Service Office in Buffalo NY (NWS BUF) chooses a theme to name lake effect snow events. Events that meet local warning criteria of 18 cm in 12 hours (23 cm in 24 hours) are given a name related to the theme. “Snakes” was the theme for the 2008-2009 season (i.e., Anaconda, Boa, Copperhead). The theme for the 2009-2010 season is “Flowers” (i.e., Amaryllis, Begonia, Carnation). Two prominent events of the past two years were Hognose (21-23 December 2008) and Amaryllis (10-12 December 2009). Both events featured “blizzard like” conditions, the eventual closure of the New York State Thruway along with numerous impassible secondary roadways, and 30 to 45 cm of snow with locally higher amounts. Most of this occurred within a 24 hour period. By NWS definition, blizzard conditions were met at KBUF for both events, with sustained wind or frequent gusts greater than or equal to 56 km/h accompanied by falling and/or blowing snow, frequently reducing visibility to less than .4 km for three hours or more. Prior to each event, careful consideration was given whether to issue a Blizzard Warning or a Lake Effect Warning combined with a High Wind Warning. In each case, the latter route was chosen partly due to the localized nature of lake effect events. For example, many areas with bare ground that might receive only a dusting of snow would certainly not experience blizzard conditions. Numerous NWS BUF products noted “blizzard like” conditions throughout each event. Historical events also played a role in the warning decision process. NWS BUF has only issued three blizzard warnings over the past 35 years. The most notable event was the “Blizzard of 1977”, (28-01 January/February 1977) where 29 people were killed. Many were found frozen in or near their buried and abandoned cars. Only about 30 cm of snow resulted from this storm, but drifts from snow blowing off the frozen Lake Erie in some cases swallowed homes. This event is so entrenched in people’s minds that one would think that every other storm pales in comparison. Other blizzards occurred on 19-21 January 1985 and 13 March 1993, where 90 cm and 60 cm were reported respectively, along two deaths due to exposure from each event. Were Hognose and Amaryllis worthy of being considered blizzards? At what point does a lake effect event with strong winds become a blizzard? Death from exposure (hypothermia) is attributed to deaths in past blizzards. Does wind chill play a role in Western NY when it comes to determining whether to issue a blizzard or instead mentioning “blizzard-like conditions” in other winter warning products? This talk will compare the two storms and discuss their blizzard potential.

1

An Investigation of the New Years 2010 Lake Effect Snow Event Using Sounding-Based Parameters

Justin Arnott NOAA/ National Weather Service Northern Indiana

An unusually prolonged lake effect snow event occurred over the Great Lakes Region during the first week of 2010. The longevity of this event was facilitated by an impressive blocking pattern that developed off of the eastern coast of North America. This block, combined with arctic high pressure over the upper Midwest allowed for a nearly steady northwest flow of arctic air over the Great Lakes resulting in a five day period of nearly continuous lake effect snow. Over portions of extreme northwest Indiana and southwest Lower Michigan as much as two feet of snow was observed.

In this study the morphology of the lake effect snow bands is examined using sounding-based parameters previously identified as important to lake effect snow evolution. An intense single band, a null event, and a snow band enhanced by seeder-feeder processes are highlighted. It will be shown that RUC-based sounding parameters provide valuable information about each of these events, helping to differentiate between periods of significant snowfall and those that yielded little or no accumulation.

The results suggest that a tool matching expected sounding parameters to past events, similar to that developed at the National Weather Service forecast office in Binghamton, NY, would be beneficial to forecast offices in the western Great Lakes region. The development of such a tool is proposed with similarities and proposed differences to the Binghamton model highlighted.

2

Lake-Enhanced Snow: Role of Lake-scale Dynamics

Greg Mann

Science & Operations Officer NOAA/NWS Detroit, MI

Snowfall induced by the Great Lakes is exhibited in a broad spectrum from isolated lake-effect convective structure to incremental increases in snowfall associated with large, well-developed mid-latitude cyclones. A special class of lake enhanced events can be characterized by a substantial increase in intensity of weak/innocuous pre-existing precipitation patterns. Ironically, many events develop under increasingly detrimental conditions for the maintenance of lake-effect convection (e.g., deep southwesterly flow in the lower-troposphere supporting warm advection and resulting in dwindling convective layer depths). This is especially true in the lee of Lakes Michigan and Huron where lake geometry appears to be more favorable. A characteristic event is presented in the context of a series of sensitivity tests highlighting the pertinent lake-scale dynamics responsible for the enhanced snowfall.

3

Forecasting the Inland Extent of Lake-Effect Snow Bands

Joe Villani, NOAA/NWS, Albany NY Michael L. Jurewicz Sr., NOAA/NWS, Binghamton NY

Jason Krekeler, State University of NY, Albany NY

Much research has been devoted to better understanding processes that govern lake- effect snow (LES) band development in the last 20-30 years. However, one aspect that has received comparatively little attention is the inland penetration of such features. The focus of this project is two-fold. First, to identify atmospheric parameters which have the greatest bearing on how far inland LES bands travel. Secondly, to develop techniques to assist operational meteorologists in the forecast process.

A number of different LES events were studied since the winter of 2007-2008 in the Eastern Great Lakes region (Lake Erie and Lake Ontario bands). From these cases, different parameters were analyzed, at strategically placed data points within, and just outside of LES bands, to see which ones consistently had the most influence on inland extent. Statistical correlations were used in this regard. The three parameters that correlated most strongly to the inland penetration of LES bands were the existence of a multi-lake/upstream moisture connection (as judged by satellite and radar imagery), mixed-layer stability (represented by Lake-850 mb and Lake-700 mb temperature differentials), and mixed-layer speed and directional shear. In general, an environment favorable for greater inland extent of LES bands was characterized by a strong, well aligned flow in the mixed-layer, and only conditional terrestrial instability (moderately to extremely unstable mixed-layer environments seemed to produce more diffuse banded structures, which did not penetrate inland very far). LES bands that featured a multi-lake connection had a much greater tendency to progress farther inland, as compared to those without an upstream moisture source.

Based on the aforementioned results, an algorithm is being developed, which will give forecasters a reasonable first approximation of inland extent, given favorable conditions for LES band formation. This technique will specifically include several of the most strongly correlated parameters. Work also continues on developing composite plots of sea-level pressure, 850 mb, and 700 mb patterns that favor multi-lake connected LES bands, for different flow regimes.

4

An Intense Northern Michigan Snowfall:8 March 2009

John Boris Meteorologist

NOAA/National Weather Service Gaylord MI

During the late afternoon and evening hours of 8 March 2009, a quick-hitting, heavy snowfall overspread northern Lower Michigan, in association with a compact but potent short wave trough lifting northeast into the Upper Great Lakes. Snowfall totals in excess of one foot (30 cm) occurred during this event, with maximum snow accumulations of 15 inches (37 cm). Much of the snowfall occurred in a 6 to 9 hour time period, with snowfall rates at times exceeding two inches (5 cm) per hour. This presentation will examine the evolution of this event, including some initial concerns regarding precipitation type, as well as some of the factors that contributed to the intense snowfall rates.

5

Synoptic and Mesoscale Factors Contributing to a Heavy Snowfall Event Across Northern Illinois December 25 and 26 2009

Nathan Marsili

NOAA/National Weather Service Chicago, IL

In late December 2009, shortly before Christmas, a dynamic and strong closed upper level low moved out of the Central Plains into the Midwest with several short wave troughs pivoting around this system. Blizzard warnings were posted for a wide swath of the nation's midsection, and the resulting snowstorm severely hampered holiday travel. The 2009 Christmas Eve Blizzard will be remembered mostly for the deadly conditions it posed to holiday travelers on December 24th and 25th. Although, even as this storm was weakening, it still maintained enough energy and moisture to produce a widespread area of 3 to 6 inch snow amounts across northern Illinois. This system and the broad area of moderate snow were well anticipated in the forecasts leading up to this event. However, a small pocket in the Chicago suburbs where snow totals nearly doubled was not. This presentation investigates the factors that contributed to this missed forecast.

While synoptic forcing related to smaller scale vorticity maxima revolving around this upper level low along with isentropic ascent were the main culprits, mid level frontogenesis was also a key feature in this event. Enhanced lift due to this mesoscale forcing coincided within a deep dendritic growth zone adding another key element to this event. The higher snow amounts observed were partially the result of extremely high snow to liquid ratios, estimated near 40 to 1 in some locations. While snow ratios of this magnitude are not unheard of, they certainly are not typical. In addition, a closed upper level low with its surface reflection passing across northwest Illinois does not typically produce 12-inch snowfall amounts across the Chicago area. This surface and upper-air pattern was not recognized as one that would traditionally be associated with such large snowfall amounts in northeast Illinois presenting yet another interesting aspect to this event.

6

The NASA Short-term Prediction Research and Transition (SPoRT) Center: Opportunities for Collaboration in the Great Lakes Region

Andrew Molthan

NASA Marshall Space Flight Center Huntsville, Alabama

The NASA Short-term Prediction Research and Transition (SPoRT) Center facilitates the transition of unique NASA observations and research capabilities to the operational weather community to help improve short-term forecasts on a regional scale. The SPoRT Center has a substantial history of partnering with National Weather Service WFOs in the Southern Region, providing numerous satellite products obtained from polar-orbiting satellites, as well as the distribution of GOES products provided by SPoRT collaborators. Efforts within SPoRT encompass the topics of remote sensing, unique lightning data for severe weather applications, data assimilation, and extensive projects related to the WRF Environmental Modeling System (WRF-EMS), available for use within individual forecast offices.

In the past year, SPoRT completed the successful transition of a unique sea surface temperature composite by incorporating the field as the default option within the current release of the WRF-EMS. These efforts have naturally transitioned to the development of Great Lakes surface temperature composites, obtained from a blend of high resolution MODIS data, AMSR-E passive microwave data, and other data sets. By incorporating the composite with NOAA/Great Lakes Environmental Research Laboratory (GLERL) ice analyses, the resulting field can be incorporated within the WRF-EMS to provide a near real-time depiction of lake temperatures with a higher degree of detail than currently available products. In addition, SPoRT is developing collaborations with the microphysics community to explore new schemes, evaluating their performance against recent field campaign measurements. This presentation will provide an overview of the NASA SPoRT project and future plans, seeking new opportunities for collaborative research within the operational forecast community.

7

Operational Great Lakes Ice Charts and On-Line Climatology

Marie-France Gauthier Canadian Ice Service, Ottawa, ON

Environment Canada A variety of ice products are available for the Great Lakes through Environment Canada’s Ice Service and the North American Ice Service (NAIS). The NAIS is a virtual organization whose members are the U.S. National Ice Service (NIC), the Canadian Ice Service (CIS) and the International Ice Patrol (IIP). The concept of the NAIS is to create a harmonized suite of operational products and services for ice information in North American waters to serve the needs of users for the safety of navigation and informed decision-making. The NAIS is officially recognized by both the US and Canadian government through the signing of the “North American Ice Service Agreement”. Through joint production procedures and shared high resolution imagery such as RADARSAT2, the NAIS provides harmonized ice charts and bulletins for the Great Lakes during the winter season. In addition, the NAIS produces a seasonal forecast that is used for planning purposes and a seasonal summary. To assist with climate studies, the Canadian Ice Service has a digital real-time archive of weekly charts going back to 1968. These charts are available from the CIS web site. An on-line Ice Graph Tool is available to easily extract and display information about the ice conditions. This is commonly used to compare the conditions with previous seasons.

8

Evaluation of Great Lakes Ice Model (GLIM) Real-time Ice Forecasts for Lake Erie during the 2009-2010 Ice Season

Robert LaPlante

NOAA/ National Weather Service Cleveland, OH

David Schwab, Jia Wang, Gregory Lang NOAA/GLERL Ann Arbor, MI

The Great Lakes Ice Model (GLIM) is an experimental numerical forecast model intended to improve the accuracy of Great Lakes ice forecasts and outlooks, open lake forecasts, near shore forecasts and marine weather statements. The GLIM runs twice per day for Lake Erie as part of the Great Lakes Coastal Forecast System (GLCFS) at NOAA/GLERL (http://www.glerl.noaa.gov/res/glcfs). GLIM is a combination of the Princeton Ocean Model for hydrodynamics and the Combined Ice Ocean Model (CIOM) ice model specifically tailored for operation in the Great Lakes. The combined lake circulation/ice model is run using the latest NWS National Digital Forecast Database (NDFD, http://www.nws.noaa.gov/ndfd) surface meteorological grids as input. Twice-a-day forecasts extend out to 5 days. The initial conditions are based on nowcast runs which incorporate the National Ice Center (NIC) ice observations and use observed meteorological data for atmospheric forcing. The integration of the GLIM and the NDFD forecast elements generates graphics and text products showing surface water temperature, ice concentration, ice thickness and ice drift. Nowcasts and forecasts of ice concentration fields are compared to twice-weekly ice analysis charts produced by the NIC as well as satellite imagery from active (SARSAT) and passive (MODIS) sensors.

9

Comparing GEM 15km, GEMLAM 2.5km and RUC 13km Model Simulations of Mesoscale Features over Southern Ontario

David Sills, Norbert Driedger and Emma Hung

Cloud Physics and Severe Weather Research Section, King City, ON Environment Canada

A variety of different numerical weather prediction models are used at the Research Support Desk in the Ontario Storm Prediction Centre to provide guidance for mesoscale analysis and nowcasting. Included among these are: • the regional version of Environment Canada’s Global Environmental Multiscale

(GEM) model with 15 km horizontal grid spacing, • the limited-area version of the GEM model (GEM-LAM) with 2.5 km horizontal

grid spacing, and • the US Rapid Update Cycle (RUC) model with 13 km horizontal grid spacing. Both the GEM-LAM 2.5 model and the RUC model are expected to have advantages over the regional GEM model. The high-resolution employed by the GEM-LAM 2.5 model should provide more accurate solutions than the regional GEM model in areas with complex topography such as southern Ontario. The RUC model is run hourly with a fresh set of initial conditions that should effectively ‘nudge’ the model solution closer to reality than the regional GEM model. To test these hypotheses, the three models were evaluated quasi-daily at 18 UTC for southern Ontario and surrounding areas from June 2008 to May 2009. Surface winds from the models were compared to winds from surface weather stations, as well as radar data and satellite imagery. The model solutions were then ranked according to their success at simulating observed mesoscale features such as lake breezes and land breezes, and the mesoscale details of synoptic-scale features such as fronts and low centres. Results show that the GEM-LAM 2.5 model and the RUC model are indeed better at simulating mesoscale features, with the relative rank of these two models depending on the feature type and the time of the year. The LAM ranked first for early- and late-season lake breezes, while RUC ranked first for low positions. Interestingly, the LAM ranked last for winter land breezes, while RUC ranked last for early- and late-season lake breezes. Examples from several days will be presented.

10

Enhancing Local Model Studies with Initial Conditions from Satellites for Great Lakes Research

Jordan Gerth

Research Assistant CIMSS/SSEC/University of Wisconsin

With increasing computing capabilities to run local, fine-mesh numerical weather prediction (NWP) simulations with limited resources, it is now possible to conduct studies of mesoscale and synoptic scale meteorological features that influence Great Lakes weather. In order to achieve greater accuracy in these high-resolution domains, it is necessary to produce initial conditions and surface data sets on the same spatial scale as the model grid. This talk looks at how the Cooperative Institute for Meteorological Satellite Studies (CIMSS) integrates observations from the Geostationary Operational Environmental Satellite (GOES) Sounder and the MODerate resolution Imaging Spectroradiometer (MODIS) with in-situ data to conduct NWP studies using the CIMSS Regional Assimilation System (CRAS), and Weather Research and Forecast (WRF) models.

Activities conducted under the GOES R-Series Proving Ground, a forecaster and user readiness exercise ahead of the 2015 launch of GOES-R, the United States’ next-generation geostationary satellite, will also be presented to show the expected increase in available satellite observations by the end of the decade, and immediate applicability to field operations. Part of the talk will focus on the developments in the study of the “pneumonia front”, a sharp convergence boundary which behaves similar to a density current and creates temperature falls in excess of 15 degrees Fahrenheit in one hour as it accelerates perpendicular to a shoreline. A 26 May 2008 case of a pneumonia front impacting eastern Wisconsin, and particularly Milwaukee, with a 37-knot squall and 23-degree temperature drop in less than an hour, will be covered.

11

Some effects of the Great Lakes on air quality in southern Ontario due to land-water temperature differences

Frank Dempsey

Air Quality Meteorologist Ontario Ministry of the Environment

Effects of the Great Lakes on air quality in southern Ontario include variations in trends of ground-level ozone, nitrogen oxides, and fine particulate matter due to land-water temperature differences during periods dominated by a high pressure ridge and in the absence of synoptic-scale forcing. Weak surface-level temperature gradients, causing pressure differences of about 1 mb or less, result in brief periods of stagnation with light or calm winds and decreased mixing of the boundary layer. These periods may last several hours and may coincide with increasing concentrations of nitrogen oxides and fine particulate matter (and increasing air quality index values) in locations with some urban pollution sources.

Several examples illustrating effects caused by the formation of mesoscale high pressure cells over the lakes during spring and summer, and mesolows over the lakes during autumn, are shown using 4-km resolution mesoscale forecast charts for southern Ontario (produced by the WRF-NMM Model in the FReSH-4 meteorological forecasting system from SENES Consultants Limited), along with concentrations of air pollutants measured at the Ontario Ministry of Environment air monitoring sites.

12

Frontogenesis Forcing and its Relation to Convective Initiation and Convective Initiation Failure in the Warm Season

Dan Miller

Science and Operations Officer, National Weather Service, Duluth MN

Phil Schumacher Science and Operations Officer, National Weather Service, Sioux Falls SD

Greg Mann

Science and Operations Officer, National Weather Service, White Lake MI Mesoscale forcing for ascent produced by the ascending branch of ageostrophic frontogenetical circulations is a commonly used forecast tool during the cold season to assess the potential for heavy banded precipitation, and in particular heavy snow. Conversely, diagnosis of frontogenesis is often de-emphasized in the warm season, presumably because deep-layer thermal gradients are weaker/less common during the warmer months of the year. However, considerable operational experience and observation, along with a baroclinic zone frequency study for the 2006 warm season conducted by the staff at WFO Duluth, MN, suggest that low-level baroclinic zones are much more common during the warm season than previously acknowledged. The frequency study also strongly suggests that mesoscale frontogentical forcing for ascent, resultant from interaction between the nose of a southerly or southwesterly low-level jet and a low-level thermal gradient, is actually a quite common forecast problem during the warm season across much of the central and eastern United States and at a minimum, adjacent areas of southern Canada. Specifically, frontogenesis forcing seems to play a critical role in the initiation of deep moist convection along and to the immediate cool side of low-level baroclinic zones, and perhaps even more intriguing, may also play a significant role in convective initiation failure in the surface warm sector. A couple of case studies will be presented, along with a conceptual model of these processes.

13

Observations of Near-Surface Thermodynamic and Wind Shear Profiles on Significant Tornado Days

Dan Miller

Science and Operations Officer National Weather Service, Duluth MN

Over the past 10 to 15 years, considerable research has contributed to a much more robust understanding of the atmospheric conditions supportive of significant tornadoes and the storms that produce them (e.g. Markowski, et al, Rasmussen, et al, Evans and Doswell, Thompson, et al and others). This research suggests, rather strongly, that much of the tornado process seems to happen at very low levels in the atmosphere (i.e. within the lowest 1000 meters above ground level). In addition, two forecast parameters in particular have emerged as being critically important in identifying meteorological environments supportive of supercell thunderstorms that are capable of producing long-tracked, strong or violent tornadoes: strong wind shear in the lowest 1000 meters above ground level, and moderate to high levels of relative humidity in the boundary layer. On many significant tornado days, a specific combination of seemingly unique thermodynamic and wind shear profiles has been observed to exist in the lowest 1000 meters kilometer of the atmosphere, and these observations are in general agreement with the findings of the most recent research. However, these thermodynamic and wind shear profiles, when combined with other visual and radar observations of storms, pose some intriguing questions regarding their frequent associative nature with significant tornado events, as well as our application of parcel theory, and the terms “elevated” and “surface-based” convection. Since choosing the “correct” parcel to “lift” is often critical in properly diagnosing the threat level associated with a given convective environment, this raises additional, and perhaps troublesome questions regarding the use of several popular near-storm environment significant tornado forecast parameters used in short term forecast and warning operations, including 1) Lowest 100 millibar Mean-Layer CAPE (MLCAPE), 2) Lowest 100 millibar Mean-Layer CIN (MLCIN), 3) surface to 1 km AGL wind shear, 4) surface to 1 km, and surface to 3 km energy-helicity index (EHI), and 5) surface to 3 km vorticity generation potential (VGP). Numerous examples of observed soundings and hodographs exhibiting this seemingly unique superposition of low level thermodynamics and wind shear will be presented, and radar and visual observations from some cases will also be shown as a basis for discussion of questions regarding parcel theory, and the use of the aforementioned severe weather indices in forecast and warning operations.

14

August 19, 2009 Northeastern Illinois and Northwest Indiana Severe Weather Outbreak: Part 1

Mark Ratzer, Andy Boxell, and Eric Lenning

National Weather Service, Chicago IL On August 19, 2009, a mature MCS moved through much of the Chicago National Weather Service Forecast Office County Warning Area. Convection from the MCS created significant wind damage across portions of the Lincoln, IL and Chicago, IL NWS WFO County Warning Areas. Late in the event, as this MCS moved east into increasingly stable air and began to dissipate, additional thunderstorm development occurred behind the MCS, with convection quickly becoming supercellular and surface-based. As this convection moved across northwestern Indiana, one of these cells spawned an EF-2 tornado in the town of Chesterton, in northern Porter County. This two-part case study explores the relevant synoptic and mesoscale-α environments before and during the severe weather outbreak. Part one of this case study focuses on the synoptic scale environment and subsequent MCS development, including both observational data and numerical model forecast considerations. Analysis of the synoptic and mesoscale environments indicated a seasonably robust short wave trough and associated surface low across the Midwest on the morning of August 19, 2009. As a warm front surged north across central Illinois and Indiana, convection developed in response to a mesoscale convective vortex. This MCV was likely the remnant of convection which developed over Kansas and Missouri during the previous 24 hours. Analysis of rawinsonde, VAD winds from the WSR-88D network, AMDAR aircraft soundings, and wind profiler data suggests that convection likely developed and became supercellular in response to a compact but strong shortwave trough and associated jet streak moving across the area coincident with the MCV. Part two of this study will center on mesoscale and storm scale environment and storm evolution.

15

August 19, 2009 Northeastern Illinois and Northwest Indiana Severe Weather Outbreak: Part 2

Andy Boxell, Mark Ratzer, and Eric Lenning

National Weather Service, Chicago IL

On August 19, 2009, a mature MCS moved through much of the Chicago National Weather Service Forecast Office County Warning Area. This MCS produced 3 confirmed tornadoes that caused EF-1 and EF-2 damage, as well as damage from strong convective winds. Part one of this case study focused on the synoptic scale environment and subsequent MCS development through analysis of observational and numerical model data. Part two of this study explores the mesoscale-β and storm-scale environments during the severe weather outbreak, with a particular focus on storm-scale changes and interactions before and during tornadogenesis. Analysis of the mesoscale and near-storm environments indicates that convection associated with a mature MCS was moving into increasingly stable air across the Chicago WFO CWA, with surface-based CAPE values ranging from around 1000 J/K across the far southern CWA to less than 100 J/K across the northern CWA. Despite the increasing stability, convection remained organized as it moved across the CWA, likely due to unseasonably strong shear values across the area. Two EF-1 tornadoes were confirmed with the initial wave of convection associated with the MCS. The first occurred within the well-developed bookend vortex, likely the result of extremely high values of environmental vorticity being stretched in the vertical by a strong convective updraft. The second EF-1 tornado, which occurred behind the main MCS, was possibly influenced by gravity wave interaction as suggested by the presence of several non-severe cells exhibiting deviant storm motion ahead of the main MCS. The final tornado, rated EF-2, occurred as a newly developed storm quickly became supercelluar and surface-based across northwestern Indiana. Radar and mesoscale analysis indicates that tornadogenesis occurred as this storm moved into an area of high surface moisture and backed surface winds and simultaneously interacted with a northward moving convective cell which also suggested the presence of gravity wave activity. Part two of this study concludes with a brief look at resulting storm damage from the three tornadic storms.

16

August 20th 2009: The Day the Skies rained Tornadoes

Arnold Ashton, Ontario Storm Prediction Centre, Toronto, ON Mike Leduc and Sudesh Boodoo

Cloud Physics and Severe Weather Research Section, King City, ON Environment Canada

On August 20 2009 between 3:30 and 10:00 PM EDT, 18 tornadoes were reported in Southern Ontario within 250 km north of a west-east line through the city of Toronto. This is the largest number of tornadoes in a single outbreak ever recorded in Canada. Four of these storms attained F2 intensity. One death was reported, and damage claims were in the tens of millions of dollars. We will map the outbreak and discuss many of the unusual aspects of the event, as well as include a wide collection of photos. One particular aspect of the storms that will be explored in some detail is the passage of four supercells that moved along a line (possibly a lake breeze) through the densely populated suburbs north of Toronto between 5 and 7 PM EDT, causing two F2 and one F1 tornadoes. Evidence, including eyewitness accounts, innumerable videos, and radar outputs (King City and Buffalo reflectivity and Doppler data, and King City polarimetric data) will be assessed. This data leads to an unusual and surprising conclusion to the sequence of tornado touchdowns in the Toronto suburbs.

17

Damage to residential construction in the August 20, 2009 tornadoes in Vaughan, Ontario

Gregory Kopp

University of Western Ontario The results of a detailed damage investigation of the two tornadoes in Vaughan, Ontario, which were part of the outbreak of 18 tornadoes on August 20, 2009, are presented. The bulk of the damage in both tornadoes consisted of structural roof failures categorized as F1 on the Fujita Scale and EF1 on the Enhanced Fujita Scale. However, multiple houses in both tornadoes suffered total roof failure, which is F2 (or EF2). It was observed that the total roof failures were all due to either internal pressurization and/or weak (or non-existent) roof-to-wall connections. Since internal pressures are likely to be significantly larger than external pressures for these single family residences, it is argued that the total roof failure occurred under wind speed conditions associated with a lower degree of damage, such that actual wind speeds are more like those in EF1.

18

The August 20th 2009 Tornado Outbreak: Synoptic overview and the challenges of forecasting an extreme event

Arnold Ashton, Ontario Storm Prediction Centre, Toronto, ON

Mike Leduc, Cloud Physics and Severe Weather Research Section, King City, ON Mark Firmin, Ontario Storm Prediction Centre, Toronto, ON

Environment Canada

The development of severe weather on Aug 20 2009 across southern Ontario was not unexpected. This paper will present composite charts and weather discussions of the synoptic situation as it developed from T-24 hours to the time of the outbreak. However, the number of supercells and the percentage of them that became tornadic were historic for Canada and the evolution of this event was rather unique. We will demonstrate this with composite radar imagery. "Traditional" numerical model guidance did provide some advanced clues to the significance of this tornado outbreak although they also presented some conflicting signals. Studies have shown that higher resolution model output is required to better forecast the spatial and temporal characteristics of severe thunderstorms. In particular, mesoscale model outputs of fields related to buoyant energy and shear have been shown to be very useful in severe storm prediction and will be assessed for August 20th as they relate to tornadic storm forecasting versus more linear, non-tornadic storms.

For comparison purposes, the results will be evaluated against a few of the more severe weather events of recent years in Ontario (both tornadic supercells and linear storms). One of the results indicates the severe weather parameter DCAPE shows some promise as a discriminator between outbreak types. Finally, the results will be summarized and linked to a recent study to suggest a philosophy of improving skill in forecasting significant severe weather outbreaks, and even differentiating storm mode. This is crucial for bolstering early preparedness for all stakeholders including emergency management prior to an event as well as improving lead-times for warnings once storms develop.

19

Examination of the low level polarimetric radar parameters associated with the Aug 20 2009 southern Ontario tornadic supercells

Mike Leduc

Radar Meteorologist Cloud Physics and Severe Weather Research Section, King City, ON

Environment Canada On Aug 20 2009 numerous supercells with strong rotations moved through southern Ontario. During the period from 2100 to 2230Z 6 of these storms were observed within 60 km of the King City radar. After an exhaustive investigation it was concluded that 4 of these supercells produced F1/F2 tornadoes while the other 2 did not. This paper will examine the structure of these 6 storms. Twelve other tornadoes were reported in southern Ontario on August 20 but will not be considered here. . The Environment Canada King City 5 cm radar has had dual polarization capability since 2004. The Aug 20 2009 outbreak provides a unique opportunity to study supercell storms at close range. This paper will concentrate on the data from a research mode high resolution 0.5 degree scan collected by King radar every 10 minutes. For our 6 close- in storms this scan elevation will give a view of the lowest parts of the storm from a few hundred metres to 1 km above the ground. Polarimetric parameters at lower resolution are collected for the full volume scan but will not be presented here. A few papers within the last couple of years have expanded the conceptual models of supercells to include polarimetric parameters. Many of the new features of this conceptual model are observed at low levels. The zdr arc and kdp foot signatures at low levels of the storm will be reviewed here and we will examine how our supercells match this model. A study of the May 2003 Oklahoma tornadic supercell exhibited an expansion and a storm relative clockwise rotation of the kdp foot at low levels as the tornado touched down. Other studies suggest that the polarimetric characteristics of the hook echo may be important in predicting whether a tornado will touch down or not. This study is very preliminary. Previous case studies are nearly all based on 10 cm radar data. A direct comparison with our storms viewed on 5 cm is fraught with difficulties.

20

The Effects of Lake Michigan on Mature Mesoscale Convective Systems

Nicholas Metz and Lance Bosart University at Albany

Warm-season mesoscale convective systems (MCSs) that traverse the Great Lakes and vicinity are of interest because of potential interactions with the typically cooler lake waters relative to the surrounding land. The increased thermal stability of a very shallow layer of air in contact with the lakes may decrease (increase) surface-based CAPE (CIN) and result MCS weakening. However, MCSs have been observed to maintain strength, or intensify, as they traverse the Great Lakes, suggesting that these MCSs may be feeding on accelerated surface flow, characteristic of adjoining land masses, that resides just above a very shallow surface-based stable dome of cold air over the Great Lakes. The purpose of this presentation will be to document mature warm-season MCSs that cross Lake Michigan and examine MCS lake interactions. Climatological results from 2002 to 2007 indicate that 43% of warm-season MCSs maintain strength upon crossing Lake Michigan. This maintenance is favored when an MCS crosses in the evening/overnight and in the mid-summer. However, maintenance can occur at other times as well, such as during the early warm season (April-June), when lake water temperatures are only 3?10°C. Thus, the lake water temperature is not a good predictor of MCS maintenance. Rather, the very shallow near-surface lake inversion (buoy air temperature at 5 m minus lake water temperature) is typically much stronger in association with MCSs that maintain, particularly in the early warm season. Additionally, MCSs tend to maintain in association with an intense low-level jet stream and a deep convective cold pool, while the amount of CAPE and shear in the environment immediately upstream of Lake Michigan does not appear to discriminate between MCSs that maintain versus those that dissipate. Selected case studies will accentuate climatological results, and attempt to highlight the differing combinations of environmental conditions that can distinguish between MCSs that maintain and those that dissipate upon crossing Lake Michigan.

21

Boundary Interactions and the Development of a Rare Classic Supercell in Northern Indiana

Jeff Logsdon

Science & Operations Officer National Weather Service Northern Indiana

On a day characterized by pulse-type thunderstorms, most of which remained below severe limits, one isolated supercell was able to develop during the late afternoon hours as a result of multiple boundary interactions. During the early morning hours of June 19, 2009 a mesoscale convective system (MCS) pushed southeast through the great lakes region ahead of a warm front that extended from the southern tip of lake Michigan through the southeast corner of our county warning area (CWA) in northwest Ohio. The resulting outflow boundary pushed the warm front south into central Indiana and provided an initial cap to any surface-based convection through the morning hours. Elevated convection was able to form around midday near the Indiana/Michigan state line above the surface cold pool. This convection pushed another strong outflow boundary south through northern Indiana. At the same time, the warm front was pushing back northward as afternoon heating overcame the stable low level air. This presentation will examine the interaction of these two boundaries and the subsequent supercell development and also explore possible explanations for tornadogenesis failure with this storm.

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MCS Initiation and Development Along Land/Lake-Induced Thermodynamic Boundaries near the Great Lakes

Alan F. Srock and Lance F. Bosart

University at Albany/SUNY

One of the primary considerations for the influence of the Great Lakes on MCS development is the horizontal potential-temperature gradient close to the surface across the land/lake boundary. This mesoscale, thermodynamic boundary often forms around a lake due to differential heating of the land and lake surfaces, and is frequently maximized in the warm season. An intense land/lake boundary can interact with surrounding environmental features and enhance forcing for ascent, which can lead to convection and MCS formation near the lake.

This study will focus on a radar climatology and selected case studies highlighting different pathways for MCS initiation and development near the Great Lakes during the warm season. The climatology will explicate the most favorable locations, land/lake conditions, synoptic conditions, and times of year for MCS initiation near the Great Lakes. Using these results, case studies and high-resolution model simulations highlighting the most relevant factors for MCS generation will be discussed, including the land-surface/lake-surface temperature contrast, the depth of the over-lake cold pool, and the direction of low-level wind direction and wind shear. Downstream of the lake, MCSs tend to initially form and then develop along the near-lake thermal/density gradient. Preliminary analyses suggest that isolated convection moving off the cool lake toward warmer land has an “apparent” cold pool in place, which can lead to MCS (re)development more rapidly into the optimal or mature stages (as discussed in Rotunno et al. 1988).

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Analysis of the May 8, 2009 Derecho and Mesoscale Convective Vortex

Edward Shimon Senior Meteorologist

National Weather Service Lincoln, IL

On May 8, 2009, an extreme progressive derecho and Mesoscale Convective Vortex (MCV) blasted across the Southern Midwest states. The system reached its most damaging phase as it moved across Southeastern Kansas, southern Missouri, and Southern Illinois. There were numerous reports of damaging non-tornadic winds associated with the derecho and MCV. Damage surveys pointed toward the occurrence of widespread straight line winds between 60 and 90 mph (97-145 km/hr). Peak wind gusts were measured over 80 mph (129 km/hr) at Marion and Carbondale, IL. The peak gust recorded by the automated system at the Carbondale airport was 81 mph (130 km/hr) before the system failed. An observer at that airport visually observed a separate anemometer located on the rooftop reach 106 mph (171 km/hr). As the system entered Southwestern Missouri, the line of storms began to produce embedded supercells. Some of the supercells produced baseball sized hail, which was an unusual occurrence for a typical derecho.

The supercells also produced numerous tornadoes, including two that reached EF-3 in strength and eleven that reached EF-2. A total of 25 tornadoes developed during the height of the storm, in Missouri and Illinois, including several in the MCV bookend vortex on the northern end of the derecho. The MCV bookend vortex formation was enhanced by a wake low that developed behind the line of storms. The northern MCV became increasingly pronounced producing a very large comma head.

Based on model simulations from the early 1990’s, observational studies documented the size of typical comma head vortices were on average 12 nm (19 km) in diameter. The comma head on the May 8th storm was 30 to 40 nm (48 to 64 km) in diameter. In fact, some experts and NWS Meteorologists indicated it was the largest bookend vortex that they had seen in their careers. Radar loops from the event showed structure similar to that of a tropical hurricane, with an eye wall evident at times in the center of the storm. This led the general public to try to classify the system as an inland hurricane. Although that was not a valid classification for this extratropical system, many experts considered it to be one of the worst derechoes and MCVs in at least the last decade. This study will look at some of the meteorological aspects that may have played a role in the development of this extreme progressive derecho and MCV. Attention will be placed on the dynamic and thermodynamic features that were present that day. Potential Vorticity (PV) and PV Anomalies will also be analyzed as to their possible role in this unusual severe weather event.

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A Cloud to Ground Lightning Climatology for the Lake Superior Region

Michael Dutter and Steven Fleegel NOAA/National Weather Service Marquette, MI

Although thunderstorms are not as frequent across the Lake Superior Region compared to other parts of the United States and Canada, lightning does pose a considerable risk to public safety, especially due to the numerous outdoor activities that occur in the late spring through early autumn months (May-September). Convective activity can come in several forms across the region, from afternoon and early evening diurnal thunderstorm activity, to late night and early morning nocturnal Mesoscale Convective Systems (MCSs). Adding to the complexity of thunderstorm development and maintenance are the Great Lakes, and the associated land/water interface, which can dramatically alter thunderstorm development, intensity and maintenance.

This study will explore cloud to ground (CG) lightning strike climatology for the Lake Superior Region during the 2002-2008 time period. In particular, the temporal and spatial distribution of CG lightning density will be examined. Flow regime CG lightning climatology, using 700 hPa winds from the North American Regional Reanalysis (NARR) (Mesinger et. al, 2006) dataset, will also be discussed.

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Investigating the Potential of Using Radar to Nowcast CG Lightning Initiation over Southern Ontario

Helen Yang

Meteorologist Ontario Storm Prediction Centre

Environment Canada The potential of using radar echo reflectivity to forecast cloud-to-ground (CG) lightning initiation in the 0-1 hr time frame was investigated in Southern Ontario. The main purpose was to determine a reflectivity threshold at an isothermal altitude and threshold for echo tops which best predict CG lightning initiation. The study examined lightning, radar, and upper air sounding data for only airmass-type convection in the summer of 2008. 40 dBZ detected at an altitude with an environmental temperature of -10ºC best predicted the onset of CG lightning, with an average lead time of 17 minutes. Echo tops reaching or exceeding seven km was a necessary condition prior to or at the time of the first CG lightning occurrence. Also, certain differences were observed depending on the polarity of initial lightning flashes. Positive lightning flashes, when compared to negative ones, tended to deliver stronger electric currents and to be farther away from the locations of highest reflectivity on maximum reflectivity (MAXR) radar products. Lead times were observed to be shorter for positive lightning, which might suggest that positive-lightning-producing storm clouds became strongly electrified faster than the negative counterparts. Findings indicate potential to develop a lightning nowcast algorithm suitable for Canadian forecast operational use.

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A Rare, Devastating Severe Weather Event in Western New York State

Tom Niziol Meteorologist In Charge

NOAA/National Weather Service Buffalo, NY On a quiet summer evening back in 2009 severe thunderstorms rolled across Western New York State. The storms produced a nearly unprecedented amount of damage across the region. In fact, estimates of monetary damage to property over a multi-county area neared $100,000,000 making this event a true catastrophe for the population affected. Portions of several counties were officially recognized as Federal Disaster Areas. Unfortunately, there was a fatality associated with the storms as well. One of the factors associated with the severe weather was the rarity of the event for western New York State. In this talk, the meteorological factors that led to the catastrophic severe weather will be presented. In addition, the Situational Awareness on the part of the WFO Buffalo forecast staff who worked that day will also be discussed. Workshop attendees will be placed into the shoes of the forecasters on duty that day and night. Then the event will be replayed to point out the level of Situational Awareness that all forecasters must exhibit when dealing with events that are beyond what can be described as “typical garden variety severe weather”.

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Improving Excessive Rainfall Forecasts at HPC by using the "Spatial Density" Approach to High Resolution Models

Michael Eckert Meteorologist

NOAA/NWS/HPC Experimental application of a "Spatial Density" procedure to rainfall forecasts from high-resolution (~4km) numerical guidance is ongoing at the Hydrometeorological Prediction Center (HPC) and National Severe Storms Lab (NSSL). This procedure accounts for the skill high-resolution models exhibit in anticipating the amplitude of heavy rainfall events, while accounting for the uncertainty in specific location. This presentation will provide an explanation of the spatial density approach, and examples of its experimental application at HPC. Particular cases will be highlighted where the approach alerted the forecaster of the likelihood of excessive rainfall when other operational guidance did not.

Climatology of Heavy Rainfall over Upper Michigan

Jonathan Banitt NOAA/National Weather Service Marquette, MI

This study examines the climatology and synoptic patterns associated with heavy rainfall events over Upper Michigan. Rainfall amounts in 24 hours exceeding two inches or more at two or more cooperative observer sites since 1966 could be partitioned into three main synoptic patterns. Illustrative cases for each pattern type will be presented. In addition, NCEP/NCAR Reanalysis Data was used to create composite and anomaly plots of various pressure, height, moisture and wind fields for each of the pattern types.

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Low Level Wind Shear at Pearson Airport

Yi (Emily) Zhou1, George Isaac2, 1, Peter Taylor1

1Graduate Program in Earth and Space Science, York University, Toronto, Ontario 2Environment Canada, Cloud Physics and Severe Weather Research Section, Toronto, Ontario Low level wind shear (∂U/∂z, where U is horizontal wind) forecasts from various weather prediction models (GEM-15 Regional, GEM-2.5 LAM and RUC-13) as well as the observed surface wind data and AMDAR (Aircraft Meteorological Data Reports) wind profile data for Pearson Airport have been analyzed. Observed low level wind shear cases and their time distribution are studied. Modeled and observed low level wind shear frequency is analyzed. Within 500 feet and 1000 feet height above ground level, the GEM-15 Regional has the best capability for low level wind shear forecasting, the second is GEM-2.5 LAM. For 1500 feet height above ground level, RUC is the best one, the second and third are GEM-15 Regional and GEM-2.5 LAM. Low level wind shears predicted from models are lower than those observed.

Comparing Lower and Middle Atmosphere Wind Measurements with Model Results

Matthew Corkum and Peter Taylor

York University Toronto, ON

Low to mid level wind forecasting is becoming increasingly more important as aviation traffic increases and as wind power becomes an important source of electrical power in Canada. As wind turbines increase in size and the percentage of electrical power produced increases, wind forecasting at hub heights of order 100m becomes more important. In Ontario, wind turbines are becoming increasingly more concentrated around the Great Lakes where the wind tends to be strongest, but most difficult to forecast due to roughness changes as well as heating and cooling from the lakes. The Ontario-Quebec VHF wind profiler radar network will consist of 10 wind profilers in southern Ontario and Quebec. These units use frequencies in the range 40 to 55 MHz and cover an altitude range of about 400 meters up to 15 km altitude. This data can assist with the evaluation of forecasts for wind energy purposes as well as other operational uses. Measurements from five of the wind profilers in Southern Ontario are now being compared with model results from the 15 km Canadian regional GEM model and the 12 km North American Mesoscale Model. Initial results will be presented.

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Decision Support Services: NWS Buffalo Operations following the Crash of Flight 3407

Judith Levan

Warning Coordination Meteorologist National Weather Service Buffalo, NY

Late in the evening of February 12, 2009 Continental Flight 3407 crashed into a house during an instrument approach to Buffalo-Niagara International Airport. Fifty lives were lost. The National Weather Service (NWS) Forecast Office in Buffalo provided decision support services during the critical period immediately after the event and throughout the recovery operations. Support included a physical presence at the Emergency Operations Center for six days following the crash, as well as continued remote support for several weeks throughout the recovery process. Relying on pre-existing office procedures, training, and outreach activities the offices’ team approach allowed the NWS to provide critical, decision making information to Federal, State and local officials. The NWS’s Forecast Office in Buffalo response to the crash will be discussed. A chronology of events, along with lessons learned and best practices will be presented.

Addressing the Nearshore Wave Forecasting Problem

Cory Behnke Operational Forecaster

NOAA/National Weather Service Detroit, MI

Despite more reliable wave height forecasts, the sparsity of real-time marine observations fosters an uncertainty, particularly within the nearshore environment. Recent feedback from the marine community in southeastern Michigan and Saginaw Bay suggests further improvements in wave height forecasts are needed. Given the motivation, limitations of the baseline Great Lakes Environmental Laboratory wave model were addressed for much of 2009 by including a shallow water consideration and an increased grid resolution to 2.5 km. A basic sensitivity examination between the multiple setups was conducted using steady state comparisons and results will be provided. With anecdotal accounts remaining the sole means of "ground truth", maintenance trips into the central waters of Saginaw Bay on 9-19-2008 and 7-17-2009 provided for a great opportunity in qualitatively assessing forecast performance.

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Ike and Ohio: The Perfect Storm

James Kosarik NOAA/NWS Cleveland, Ohio Peter C. Manousos First Energy Corporation, Akron, Ohio

The remnants of Hurricane Ike and associated damaging winds struck Ohio on 14 September 2008. The storm may go down as the costliest storm in Ohio history with insured losses estimated at 1.1 billion dollars (USD). Six fatalities were reported in Ohio and millions lost power as a result of the storm. We will examine the meteorological circumstances that made a weakening extra-tropical low pressure system reinvigorate into a mid-latitude record-setting storm. The storms’ damaging winds were the result of optimum mixing conditions that brought down 60 to 80 mph winds from aloft. The prolonged period of damaging winds, which occurred over several hours, was much longer than climatologically typical. Trees in full canopy exposed to the long duration of wind contributed to the many tree failures and the associated damage. Most of the injuries and fatalities in Ohio were directly connected to incidents with falling trees. First Energy Corporation, the local electric company, will share their perspective, preparation and response to the storm.

Forecasting at the Vancouver 2010 Winter Games

Arnold Ashton Lead Meteorologist

Ontario Storm Prediction Centre Environment Canada

A forecasting team consisting of MSC, NWS and The Weather Network meteorologists supported the Vancouver 2010 Olympic and Paralympic Winter Games, held Feb 12-28th. There was also a supporting research component focused on the Nowcasting project, SNOW-V10, comprised of a wide variety of state-of-the-art technology, which were available to all forecasters. An overview of the Olympic venues will be presented, along with a brief summary of the pre-Games training requirements, highlights of many of the forecast challenges and issued products, and a summary of the SNOW-V10 support including the newest numerical modeling systems. Finally, the overall flavour of the entire experience will be conveyed.