David Bright NOAA/NWS/Storm Prediction Center Science Support Branch Norman, OK

Storm Prediction Center Storm Prediction Center Forecast and Guidance Forecast and Guidance

Information for High-Impact Information for High-Impact Hazardous Weather Support Hazardous Weather Support

Where Americas Climate and Weather Services Begin

David BrightNOAA/NWS/Storm Prediction Center

Science Support BranchNorman, OK

All Hazards Workshop6-7 February 2008

Memphis, TN

Nine NWS National Centers

• Hail, Wind, Tornadoes

• Excessive rainfall

• Fire weather

• Winter weather

STORM PREDICTION CENTERSTORM PREDICTION CENTER HAZARDOUS PHENOMENA

• Framework for uncertainty

• Decision making in uncertain environments– Subjective– Precise descriptions (quantitative)

Hazardous Weather Forecasting • The Challenge: High impact events often occur on temporal and spatial scales below the resolvable resolutions of most observing and forecasting systems

• Key premise: We must use knowledge of the environment and non-resolved processes to determine the spectrum of possible hazardous weather, where and when it may occur, and how it may evolve over time

Hazardous Weather Forecasting• Observational data and diagnostic tools

– Key input for short-term prediction, i.e., “Nowcast”

– But high-impact weather events typically occur on scales smaller than standard observational data

– Environment not sampled sufficiently to resolve key fields (especially 4D distribution of water vapor)

• Model forecasts

– Supplement observational data in short term

– Increasing importance beyond 6-12 hr

– Typically do not resolve most severe phenomena

– NWP errors are related to both analysis errors and numerics/physics errors

• Recognize the inherent uncertainty and address it through probabilistic or confidence-based products

The Evolution of the Forecast

National Academy of Sciences report (2006):

• “Uncertainty is … a fundamental characteristic of weather, seasonal climate, and hydrological prediction, and no forecast is complete without a description of its uncertainty.”

• “As forecast skill has increased in recent years, forecasts have become an important component of everyday and hazardous-weather decision making for many segments of society and the U.S. economy.”

• “The entire enterprise should take responsibility for providing products that effectively communicate forecast uncertainty information.”

Source: “Completing the Forecast” http://www.nap.edu/catalog/11699.html

NCEP Strategic Plan: “Improve the user’s decision-making capabilities by including levels of forecast uncertainty in products and services.”

The Evolution of the Forecast: 2008

• 15 years experience now in ensemble prediction in the US• Steady progress in making ensemble guidance more useful and

skillful (and available!)• Increasing penetration of ensemble guidance into generation of

high-impact forecasts, e.g., severe-storm forecasts, winter and fire weather.

• Many WFOs and National Centers beginning to issue probabilistic or uncertainty forecasts– The system is evolving the public and mass communication

sources toward probabilistic thinking– Many NWS products still largely deterministic

Forecast Needs Vary from User to User

So what’s the deal with all this uncertainty? What can I do with a 10% chance of rain?

Just tell me if it’s going to rain or not.

They would if they could, my friend! But

considering uncertainty information makes

deterministic forecasts better, and adds value

for some decision makers.

Examples of Expressing Uncertainty

Although not quantified,AFDs express forecastconfidence and uncertainty

Probabilistic Forecasting at the SPC

• Severe Convective Weather• Outlooks• Watches

Convective OutlooksCategorical Forecast

Characterizes the overall threat through a single deterministic forecast

CONVECTIVE OUTLOOKSCategorical and Probabilistic: Operational through Day 8

Tornado (Hatched area 10% > EF2)

Wind Hail (Hatched area 10% > 2”)

Probabilistic forecasts provides additional information on confidenceProbability of severe event within 25 miles of a point

Hail Reliability (2006 Final)

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Verification of Probabilistic OutlooksHail (Initial Day 1, 2006)

Significant hail forecast (hatched area)

Wind Reliability (2006 Final)

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Verification of Probabilistic OutlooksWind (Initial Day 1, 2006)

Tornado Reliability (2006 Final)

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Verification of Probabilistic OutlooksTornado (Initial Day 1, 2006)

Significant tornado forecast (hatched area)

You can effectively gauge the likelihood of significant tornadoes within each watch

Severe Weather WatchesProbabilistic Table

(All watches are not created equal)

Use the probabilities to refine the specific threat within the watch and gauge forecaster confidence in the specific convective hazards

Two-Tor Watch (2006 Final)

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Verification of Watch ProbabilitiesTwo or More Tornadoes (2006)

SigTor Watch (2006 Final)

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Verification of Watch ProbabilitiesOne or More Significant Tornadoes (2006)

> EF2

You can effectively gauge the likelihood of significant tornadoes within each watch

Experimental Enhanced Thunderstorms OutlooksExperimental Enhanced Thunderstorms Outlooks(Space and probabilistic decomposition of the (Space and probabilistic decomposition of the

General Thunderstorm Line)General Thunderstorm Line)

Thunderstorm Graphic valid until 3Z Thunderstorm Graphic valid 3Z to 12Z

http://www.spc.noaa.gov/products/exper/enhtstm/

Verification of Enhanced Outlooks (All Forecasts, Past 90 days ending 01 Feb 2008)

Verification of Enhanced Outlooks (Example of a single forecast: Jan 30, 2008)

Guidance Addressing Uncertainty

• Deterministic models reveal one end state, while ensembles – Provide a range of possible forecast solutions, yielding

information on forecast confidence and uncertainty (probabilities)

• Ensemble systems supplement traditional (higher resolution) deterministic models

• Ensemble systems aid in decision support– Particularly if guidance calibrated (i.e., correct for

systematic model bias and deficiencies in spread)

Severe Event of April 7, 2006• First ever Day 2 outlook High Risk issued by SPC • More than 800 total severe reports

– 3 killer tornadoes and 10 deaths

• SREF severe weather fields aided forecaster confidence

Click on the fhour to activate dSREF/dt capability

SREF Probability of STP Ingredients: Time Trends

48 hr SREF Forecast Valid 21 UTC 7 April 2006

Prob (MLCAPE > 1000 Jkg-1)

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Prob (6 km Shear > 40 kt)

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Prob (0-1 km SRH > 100 m2s-2)

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Prob (MLLCL < 1000 m)

X

Prob (3h conv. Pcpn > 0.01 in)

Shaded Area Prob > 5%

Max 40%

SREF Probability of STP Ingredients: Time Trends

36 hr SREF Forecast Valid 21 UTC 7 April 2006

Prob (MLCAPE > 1000 Jkg-1)

X

Prob (6 km Shear > 40 kt)

X

Prob (0-1 km SRH > 100 m2s-2)

X

Prob (MLLCL < 1000 m)

X

Prob (3h conv. Pcpn > 0.01 in)

Shaded Area Prob > 5%

Max 50%

SREF Probability of STP Ingredients: Time Trends

24 hr SREF Forecast Valid 21 UTC 7 April 2006

Prob (MLCAPE > 1000 Jkg-1)

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Prob (6 km Shear > 40 kt)

X

Prob (0-1 km SRH > 100 m2s-2)

X

Prob (MLLCL < 1000 m)

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Prob (3h conv. Pcpn > 0.01 in)

Shaded Area Prob > 5%

Max 50%

SREF Probability of STP Ingredients: Time Trends

12 hr SREF Forecast Valid 21 UTC 7 April 2006

Prob (MLCAPE > 1000 Jkg-1)

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Prob (6 km Shear > 40 kt)

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Prob (0-1 km SRH > 100 m2s-2)

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Prob (MLLCL < 1000 m)

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Prob (3h conv. Pcpn > 0.01 in)

Shaded Area Prob > 5%

Max 50%

Severe Event of April 7, 2006• First ever Day 2 outlook High Risk issued by SPC • More than 800 total severe reports

– 3 killer tornadoes and 10 deaths

• SREF severe weather fields aided forecaster confidence

Uncertainty Exists in Every Prediction

SPC Fire Weather Outlooks• To provide national fire weather guidance for use by the National

Weather Service, as well as other federal, state, and local government agencies 

• The products are intended to delineate areas of the contiguous U. S. where the forecast weather conditions, combined with pre-existing fuel conditions, result in a significant threat for wildfires 

• Issued once per day during the overnight hours (through 8 days)

• Critical, Extremely Critical, and Critical Dry Thunderstorm forecasts– Low RH– Moderate / strong winds– Antecedent conditions / drought (NFDRS)– Critical area for dry thunderstorms implies

widespread lightning with minimal rainfall

Day -7 (Monday Oct, 15 2007)

Harris Fire at midday on October 23, 2007

Key Points: Confidence in western ridging increases considerably Additional support for an high-amplitude / offshore flow pattern

Ensemble 00Z 15 October 2007 (Forecast hour = 168)

168h Forecast Valid 00 UTC 22 Oct 2007

GEFS Ensemble Mean: 500 mb Height and Vorticity

168h Forecast Valid 00 UTC 22 Oct 2007

GEFS Ensemble Spaghetti: 500 mb Height (Single contour at 5760 m)

GEM Ensemble Spaghetti: 500 mb Height (Single contour at 5700 m)

Verifying analysis

168h Forecast Valid 00 UTC 22 Oct 2007

168h Forecast Valid 00 UTC 22 Oct 2007

NAEFS Ensemble: 500 mb Mean Height and its Standard Deviation

168h Forecast Valid 00 UTC 22 Oct 2007

GEFS Ensemble: Mean 500 mb Height and its Departure from Normal (# of SD)

168h Forecast Valid 00 UTC 22 Oct 2007

GEFS Ensemble Mean: PMSL; 1000-500 mb Thickness; 10m Wind (mph)

168h Forecast Valid 00 UTC 22 Oct 2007

GEFS Ensemble: Mean 2m RH (%) and its Standard Deviation

Breezy, dry airmass

...DISCUSSION... AN ACTIVE WEATHER PATTERN WILL CONTINUE THROUGH THE PERIOD BUT

FIRE WEATHER CONCERNS WILL LIKELY REMAIN SUB-CRITICAL.

AN UPPER TROUGH WILL BE OVER THE CNTRL PLAINS ON DAY 3 10/17 AND WILL DEEPEN AS IT MOVES NEWD INTO THE MIDWEST/OH VALLEY BY DAY 5 10/19. RELATIVELY COOL BUT DRY WEATHER WILL PREVAIL BEHIND THIS SYSTEM ACROSS THE SWRN STATES BEFORE ANOTHER SUBSTANTIAL TROUGH DEVELOPS OVER THE NW AND MOVES ACROSS THE ROCKIES INTO THE PLAINS FROM 10/20 - 10/21. MODELS DIFFER WITH BOTH AMPLITUDE AND LATITUDE OF THIS TROUGH. IF THE MORE AMPLIFIED SOLUTION VERIFIES LIKE THAT OF THE ECMWF...THEN A SIGNIFICANT OFFSHORE/SANTA ANA WIND EVENT COULD TAKE PLACE ACROSS SRN CA.

Day -5 (Wednesday Oct, 17 2007)

Satellite image on October 24, 2007

Key Points: Relatively high confidence in western ridge and offshore / Santa Ana wind event

Ensemble 00Z 17 October 2007 (Forecast hour = 120)

120h Forecast Valid 00 UTC 22 Oct 2007

GEFS Ensemble Mean: 500 mb Height and Vorticity

120h Forecast Valid 00 UTC 22 Oct 2007

GEFS Ensemble Spaghetti: 500 mb Height (Single contour at 5760 m)

120h Forecast Valid 00 UTC 22 Oct 2007

GEFS Ensemble: Mean 500 mb Height and its Departure from Normal (# of SD)

120h Forecast Valid 00 UTC 22 Oct 2007

GEFS Ensemble Mean: PMSL; 1000-500 mb Thickness; 10m Wind (mph)

120h Forecast Valid 00 UTC 22 Oct 2007

GEFS Ensemble: Mean 2m RH (%) and its Standard Deviation

Windy, very dry airmass

...DISCUSSION... LATEST MEDIUM RANGE DETERMINISTIC MODELS/ENSEMBLES SUGGEST THE

NEXT IN A SERIES OF UPPER TROUGHS WILL LIKELY CROSS THE WESTERN STATES THIS WEEKEND. MODEL CONCENSUS SUGGESTS THIS UPPER TROUGH MAY ULTIMATELY BECOME CUT-OFF OVER THE SOUTHWEST STATES...ALTHOUGH CONSIDERABLE DISCREPANCY EXISTS IN THE PLACEMENT DETAILS. REGARDLESS...IN THIS WAKE OF THIS SYSTEM...IT APPEARS AN OFFSHORE/SANTA ANA WIND EVENT MAY BECOME ESTABLISHED ACROSS SOUTHERN CA BY LATE DAY 4/SATURDAY AND DAY 5/SUNDAY INTO DAY 6/MONDAY. AS SUCH...THE POTENTIAL WOULD EXIST FOR NOCTURNALLY-ENHANCED GUSTY WINDS ACROSS SOUTHERN CA...ALONG WITH WARMER TEMPERATURES AND LOWER RH VALUES.

Day -4 (Thursday Oct, 18 2007)

A helicopter scoops water from a golf course in Valencia, CaliforniaAP Photo/Kevork Djansezian

Key Points: Strong western ridge (ensemble mean +2 SD)Uncertainty in location/strength of trough, but mdt-stg Santa Ana likely

Ensemble 00Z 18 October 2007 (Forecast hour = 96)

096h Forecast Valid 00 UTC 22 Oct 2007

GEFS Ensemble Mean: 500 mb Height and Vorticity

096h Forecast Valid 00 UTC 22 Oct 2007

GEFS Ensemble Spaghetti: 500 mb Height (Single contour at 5760 m)

096h Forecast Valid 00 UTC 22 Oct 2007

GEFS Ensemble: Mean 500 mb Height (m) and its climatologically normalized SD

Ensemble SpreadClimate Spread

Normalized Spread =

096h Forecast Valid 00 UTC 22 Oct 2007

GEFS Ensemble: Mean 500 mb Height and its Departure from Normal (# of SD)

096h Forecast Valid 00 UTC 22 Oct 2007

GEFS Ensemble Mean: PMSL; 1000-500 mb Thickness; 10m Wind (mph)

096h Forecast Valid 00 UTC 22 Oct 2007

GEFS Ensemble: Mean 2m RH (%) and its Standard Deviation

Very windy, very dry airmass

...DISCUSSION... LATEST MEDIUM RANGE DETERMINISTIC MODELS/ENSEMBLES SUGGEST THE NEXT IN A

SERIES OF UPPER TROUGHS WILL LIKELY CROSS THE WESTERN STATES THIS WEEKEND. CONSIDERABLE MODEL DISCREPANCY EXISTS IN REGARDS TO THE PROGRESSION OF THIS SYSTEM...WITH THE 00Z EUROPEAN SUGGESTING THE TROUGH COULD BECOME CUT-OFF OVER THE SOUTHERN ROCKIES.

INITIALLY ON DAY 3/SATURDAY...STRONG GUSTY WINDS ASSOCIATED WITH THE UPPER TROUGH/STRONG JET COULD YIELD AT LEAST NEAR-CRITICAL CONDITIONS ACROSS THE SOUTH CENTRAL HIGH PLAINS. THEREAFTER...IN THE WAKE OF THE UPPER TROUGH...CONFIDENCE CONTINUES TO INCREASE THAT A MODERATE-STRONG OFFSHORE/SANTA ANA WIND EVENT MAY BECOME ESTABLISHED ACROSS SOUTHERN CA BY LATE DAY 3/SATURDAY AND DAY 4/SUNDAY THROUGH DAY 6/TUESDAY. AS SUCH...THE POTENTIAL WOULD EXIST FOR NOCTURNALLY-ENHANCED GUSTY WINDS ACROSS SOUTHERN CA...ALONG WITH WARMER TEMPERATURES AND LOWER RH VALUES INTO EARLY NEXT WEEK.

Day -3 (Friday Oct, 19 2007)

A back fire on a hillside in Jamul, CaliforniaAP Photo/Kevork Djansezian

Key Points: Shift focus to the Short Range Ensemble Forecast (SREF) Begin to examine mesoscale details and diagnostics

AP Photo/Rick Bowmer

SREF Ensemble 21Z 18 October 2007 (Forecast hour = 75)

SREF Products Available on the SPC WebsiteSREF Products Available on the SPC Websitehttp://www.spc.noaa.gov/exper/sref/

SREF 500 mb Mean Height, Wind, Temp

SREF 500 mb Height (Spaghetti = 5700 m)

SREF Mean PMSL, 10m Wind, Thickness

SREF 10 meter Maximum Wind (any member)

SREF Pr[WSPD > 20 mph] and Mean WSPD = 20 mph (dash)

SREF 700 mb Mean Wind (kts)

SREF Mean 2m Dew Point Temperature

SREF Pr[RH < 15%] and Mean RH = 15% (dash)

SREF Pr[RH < 10%] and Mean RH = 10% (dash)

Pr [P12I < 0.01”] XPr [RH < 15%] XPr [WSPD > 20 mph] XPr [TMPF > 60F]

SREF Combined or Joint Probability

Critical Conditions

SREF Combined or Joint Probability

Pr [P12I < 0.01”] XPr [RH < 15%] XPr [WSPD > 30 mph] XPr [TMPF > 60F]

High-end Critical Conditions

SREF Combined or Joint Probability

Pr [P12I < 0.01”] XPr [RH < 10%] XPr [WSPD > 30 mph] XPr [TMPF > 60F]

Extremely Critical Conditions

SREF Median Fosberg Index + Union (red)Fosberg Fire Weather Index (FFWI)Non-linear, empirical relationship between weather and

fire behavior.

FFWI = F(Wind speed, RH, Temperature) 0 < FFWI < 100 FFWI > ~50-60 significant conditions FFWI > ~75 extreme conditions

Union: At least one member > 50

Median

SREF Pr[Fosberg Index > 70] and Mean FFWI = 70

SREF Maximum Fosberg Index (any member)

Extreme values

Examine the Individual Member Forecasts (Plumes)http://www.spc.nssl.noaa.gov/exper/sref/plume

2m Relative Humidity Plumes

Clustering by modelGood agreement RH ~5-10%

10m Wind Speed Plumes

Sustained winds 15-30 mph; clustered by model

Fosberg Fire Weather Index Plumes

FFWI values from 40-80; clustered by model; well over 50% > 60

...DISCUSSION... LATEST MEDIUM RANGE DETERMINISTIC MODELS/MREF ENSEMBLES CONTINUE TO

SUGGEST THAT THE NEXT UPPER TROUGH WILL CROSS THE WESTERN/CENTRAL STATES THROUGH DAY 3/SUNDAY...POSSIBLY BECOMING CUT-OFF/STALLING ACROSS THE SOUTHERN PLAINS EARLY NEXT WEEK. INITIALLY ON DAY 3/SUNDAY...STRONG GUSTY WINDS ASSOCIATED WITH THE UPPER TROUGH/STRONG JET COULD YIELD AT LEAST NEAR-CRITICAL CONDITIONS ACROSS THE SOUTH CENTRAL HIGH PLAINS.

AS HIGH PRESSURE PERSISTS ACROSS THE GREAT BASIN LATE THIS WEEKEND THROUGH EARLY NEXT WEEK...IT APPEARS A POTENTIALLY STRONG OFFSHORE/SANTA ANA WIND EVENT WILL OCCUR FROM EARLY DAY 3/SUNDAY INTO AT LEAST DAY 5/TUESDAY. THE POTENTIAL WILL EXIST FOR NOCTURNALLY-ENHANCED GUSTY WINDS ACROSS SOUTHERN CA...ALONG WITH WARMER TEMPERATURES AND LOWER RH VALUES THROUGH EARLY NEXT WEEK. THESE CONDITIONS...ALONG WITH EXTREME DROUGHT...SUGGEST A CONSIDERABLE FIRE DANGER WILL EXIST ACROSS SOUTHERN CA.