Storm Prediction Center Forecast and Guidance Information for High-Impact Hazardous Weather Support Where Americas Climate and Weather Services Begin David Bright NOAA/NWS/Storm Prediction Center Science Support Branch Norman, OK All Hazards Workshop 6-7 February 2008 Memphis, TN

Nine NWS National Centers

STORM PREDICTION CENTER MISSION STATEMENT The Storm Prediction Center (SPC) exists solely to protect life and property of the American people through the issuance of timely, accurate watch and forecast products dealing with tornadoes, wildfires and other hazardous mesoscale weather phenomena. MISSION STATEMENT The Storm Prediction Center (SPC) exists solely to protect the life and property of the American people through the issuance of timely, accurate watch and forecast products dealing with hazardous weather phenomena.

Hail, Wind, Tornadoes Excessive rainfall Fire weather Winter weather STORM PREDICTION CENTER HAZARDOUS PHENOMENA

Outline The SPC’s Hazardous Weather Program Forecasts Available on the SPC Website –Categorical and Probabilistic Guidance Available on the SPC Website –Mesoscale objective analysis –Short-range ensemble guidance –Additional datasets Data Available on the SPC Website –Mesoanalysis archive –Severe weather events page –Reports –Forecast product archive Summary

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” 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: 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.

- NWP models... - All forecasts contain errors that increase with time - Doubling time of small initial errors ~1 to 2 days - Maximum large-scale (synoptic to planetary) predictability ~10 to 14 days - Ensembles… - A collection of models that provide information on the range of plausible forecasts and extend predictability - Increasing in popularity - Requires “tools” to view the large number of models using a slightly different approach (statistical) Weather forecasting: It’s impossible to be deterministically correct all of the time!

Examples of Expressing Uncertainty Although not quantified, AFDs express forecast confidence and uncertainty

Examples of Expressing Uncertainty From WFO Milwaukee/Sullivan

Many examples of Uncertainty Products ProductProducerMeans of Estimating UncertaintyMeans of Communicating AFDWFOsForecaster confidence, subjectiveText NDFD -POP -SPC convective outlook -TPC wind speed probabilities -CPC 8-14 day outlook WFOs/SPC/ TPC/CPC Forecaster confidence, NWP, MOSGridded Data Point ‘n Click (POP)WFOsForecaster confidence, NWP, MOSICONs Meteograms AFM (pop)WFOsForecaster confidence, NWP, MOSText PFM (pop)WFOsForecaster confidence, NWP, MOSText SFP/SFT (pop)WFOsForecaster confidence, NWP, MOSText ZFP (pop)WFOsForecaster confidence, NWP, MOSText CWF (pop)Coastal WFOsForecaster confidence, NWP, MOSText GLF/NSH (pop)Great Lakes WFOsForecaster confidence, NWP, MOSText HWOWFOsForecaster Confidence, Numerical Weather ModelsGraphics, Text FWF (chance wetting rain)WFOsForecaster confidence, NWP, MOSText NPW (non-precipitation weather warning) WFOsForecaster Confidence, Numerical Weather ModelsText WSW (winter storm watch)WFOsForecaster Confidence, Numerical Weather ModelsText ESF (flood potential)WFOsForecaster Confidence, Numerical Weather ModelsText HLSWFOsNumerical Weather Model, Forecaster InputGraphics, Text Degree of ConfidenceWFO MKXNumerical Weather Model, Forecaster Input uncertainty Graphics Swell HeightWFO HNLForecaster input, Numerical Weather Model, Ocean ModelText, Table Probabilistic SnowfallWFO PHIForecaster Input, Statistics Tabular, Text Probabilistic SnowfallWFO BUFForecaster Input, Statistics Tabular, Text County rainfall exceedance probabilities WFO TULForecaster Input, Statistics Graphical, Text Graphical Event DiscussionWFO OUNAll available guidance Graphical

Probabilistic Forecasting at the SPC Severe Convective Weather Outlooks Watches

Convective Outlooks Categorical Forecast Characterizes the overall threat through a single deterministic forecast

CONVECTIVE OUTLOOKS Categorical and Probabilistic: Operational through Day 8 Tornado (Hatched area 10% > EF2) WindHail (Hatched area 10% > 2”) Probabilistic forecasts provides additional information on confidence Probability of severe event within 25 miles of a point

Verification of Probabilistic Outlooks Hail (Initial Day 1, 2006) Significant hail forecast (hatched area)

Verification of Probabilistic Outlooks Wind (Initial Day 1, 2006)

Verification of Probabilistic Outlooks Tornado (Initial Day 1, 2006) Significant tornado forecast (hatched area) You can effectively gauge the likelihood of significant tornadoes within each watch

Severe Weather Watches Probabilistic 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

Verification of Watch Probabilities Two or More Tornadoes (2006)

Verification of Watch Probabilities One or More Significant Tornadoes (2006) > EF2 You can effectively gauge the likelihood of significant tornadoes within each watch

Experimental Enhanced Thunderstorms Outlooks (Space and probabilistic decomposition of the General Thunderstorm Line) Thunderstorm Graphic valid until 3ZThunderstorm Graphic valid 3Z to 12Z

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 d SREF/dt capability

Pr [MLCAPE > 1000 J/kg] X Pr [MLLCL < 1000 m] X Pr [0-1KM HLCY > 100 m^2/s^2] X Pr [0-6 KM Shear > 40 kts] X Pr [C03I > 0.01”] SREF Combined or Joint Probability: STP Ingredients Probability of Significant Tornado Environment

SREF Probability of STP Ingredients: Time Trends 48 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 m 2 s -2 ) X 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 m 2 s -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 ) X Prob (6 km Shear > 40 kt) X Prob (0-1 km SRH > 100 m 2 s -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 12 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 m 2 s -2 ) X Prob (MLLCL < 1000 m) X 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, ) 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

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; 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/ /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, ) 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; 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, ) A helicopter scoops water from a golf course in Valencia, California AP 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 Standard Deviation

096h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble: Mean 500 mb Height (m) and its climatologically normalized SD Ensemble Spread Climate 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; 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, ) A back fire on a hillside in Jamul, California AP 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 Website

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 Pr[P24I >.01”] and Mean P24I =.01” (dash)

SREF Mean 2m Temperature

SREF Mean 2m Dew Point Temperature

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

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

SREF Minimum RH (any member)

Pr [P12I < 0.01”] X Pr [RH < 15%] X Pr [WSPD > 20 mph] X Pr [TMPF > 60F] SREF Combined or Joint Probability Critical Conditions

SREF Combined or Joint Probability Pr [P12I < 0.01”] X Pr [RH < 15%] X Pr [WSPD > 30 mph] X Pr [TMPF > 60F] High-end Critical Conditions

SREF Combined or Joint Probability Pr [P12I < 0.01”] X Pr [RH < 10%] X Pr [WSPD > 30 mph] X Pr [TMPF > 60F] Extremely Critical Conditions

Diagnostics and Analysis Example: Fosberg Fire Weather Index (FFWI) –A nonlinear empirical relationship between meteorological conditions and fire behavior. (Fuels are not considered!) –Derived to highlight the fire weather threat over “small” space and time scales FFWI = F (Wind speed, RH, Temperature)  0 < FFWI < 100  FFWI > ~50-60  significant fire weather conditions  FFWI > ~75  extreme fire weather conditions

SREF Mean Fosberg Fire Weather Index

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 > 60] and Mean FFWI = 60

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

SREF Maximum Fosberg Index (any member) Extreme values

Examine the Individual Member Forecasts (Plumes)

2m Relative Humidity Plumes Clustering by model Good agreement RH ~5-10%

10m Wind Speed Plumes Sustained winds mph; clustered by model

Fosberg Fire Weather Index Plumes FFWI values from 40-80; clustered by model; well over 50% > 60

Point Value: Probability Fosberg Index > 65 Despite clustering, over ½ the models predict a FFWI > 65

Point Value: Joint or Combined Probability Pr[T > 60 F] Pr[V > 20 mph] Pr[RH < 10%] Product of the three

...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.