The HPC Surface Desk M. Sean Ryan NOAA/NCEP/Hydrometeorological
Prediction Center 1
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HPC Surface Desk Responsibilities Products 3 hourly North
American Surface Analyses Storm Summaries Tropical Advisories
National Forecast Chart Users WFOs Media Aviation Government
Officials Public 2
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Unified Surface Analysis The Hydrometeorological Prediction
Center (HPC) Surface Desk creates the North American Surface
Analysis product every 3 hours. (00Z, 03Z, 06Z..) Unified surface
analysis created every 6 hours (00Z, 06Z) HPC analysis deadline is
+1:30 NHC 3
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Surface analysis is a combination of science and art Time
constraints: ~60 minutes to complete North American analysis
Different analysts have different backgrounds/experience 4 HPC
Surface Analysis Process From Uccellini et al. (1992)
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NCEP criteria for a front: Minimum of 10 deg F over 300 nm
(smaller gradients needed over oceans) 6 deg C / 500 km Cold front
leading edge of density discontinuity Warm front equatorward edge
of density discontinuity Trough positioned along zone of
convergence Lake breeze/baroclinic zones often meet this criterion,
but on such a small scale they do not get analyzed as fronts, but
rather, as surface troughs, similar to an outflow boundary Dry
lines look for 20 degree dew point gradient, with minimum 55 degree
F dew point in moist air Squall lines, outflow boundaries, coastal
fronts 5 HPC Surface Analysis Process
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Fronts are drawn manually, isobars are partially automated
(first guess provided by GFS) Manual edits based on surface
observations and model (GFS/RUC/RAP) frontogenesis, theta,
thickness fields, satellite/radar Previous analysis overlaid to
maintain continuity HPC Surface Analysis Process 6
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7 Example Wake low/mesohigh
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8 Example Lake breeze
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Fronts in the Great Lakes Region From Payer et al. (2011), the
number and type of fronts analyzed by HPC across the Great Lakes
region from January 2000 to December 2005. 9
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Fronts in the Great Lakes Region From Payer et al. (2011), the
frequency of fronts and type by lake, normalized by lake area, from
January 2000 to December 2005. 10
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The Challenges of Surface Analysis in the Great Lakes
Distinguish lake-induced baroclinic zones from fronts Lake-induced
deepening of surface lows Hurricane Huron, September 11-15, 1996
From Miner et al. (2000) 11
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The Challenges of Surface Analysis in the Great Lakes 12 MSLP
and surface frontogenesis from the RAP32
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Storm Summaries Issued for major winter weather events and
heavy rainfall/flash flooding events affecting multiple WFO county
warning areas, commerce and transportation, and are likely to
attract media attention. Issuance times: 03Z, 09Z, 15Z, 21Z
Sections include Description of what is happening now (position of
the low, precipitation, wind) Rain/Snow/Wind Reports Forecast
Precipitation Data Sources: METAR 6-hourly precipitation (compiled
by running a script), CoCoRaHS, CO-OP, PNS, LSR Also include high
wind reports (>50 mph) within the past 6 hours 13
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Tropical Advisories Issued after NHC discontinues advisories on
subtropical or tropical cyclones that move inland in the
continental United States or Mexico, which still pose a threat of
flash flooding. Advisories end when threat of flash flooding has
ended Format the same as NHC advisories, with the addition of
rainfall totals Summary Watches/Warnings Discussion and 48-Hour
Outlook Hazards Rainfall Totals Next Advisory Forecast Positions
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National Forecast Chart Highlights areas of hazardous weather
potential Composite product of: HPC Short Range Instantaneous
Precipitation Forecasts Short Range Front Forecast Excessive
Rainfall Outlook (HPC) Heavy Snow/Freezing Rain Outlooks (HPC)
Convective Outlook (SPC) Tropical Cyclone Forecast Position (NHC)
Day 1 (issued 5 AM/PM) Day 2/3 (issued 5 AM) 17
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Summary The HPC Surface Desk duties include: 3-hourly surface
analyses Storm summaries/tropical advisories National Forecast
Chart Troughs are the feature most often analyzed across the Great
Lakes region. Lake Ontario has the most fronts analyzed per unit
area, with cold fronts the most common. Thermodynamics associated
with the lakes create challenges for surface analysis Lake-induced
baroclinic zones/lake breezes Diabatic heat transfer augments low
development 18