Ensemble Usage at the SPC: Current Status and Future Plans

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Ensemble Usage at the SPCCurrent Status and
Future Plans

• David Bright
• NOAA/NWS/NCEP/Storm Prediction Center
• Norman, OK
• NCEP 3rd Ensemble User Workshop
• 31 October 2006

Where Americas Climate and Weather Services Begin
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STORM PREDICTION CENTER
HAZARDOUS PHENOMENA

• Hail, Wind, Tornadoes
• Excessive rainfall
• Fire weather
• Winter weather

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SPC Forecast Products

• TORNADO SEVERE THUNDERSTORM WATCHES
• WATCH STATUS MESSAGE
• CONVECTIVE OUTLOOK
• Day 1 Day 2 Day 3 Days 4-8
• MESOSCALE DISCUSSION
• Severe Thunderstorm Potential/Outlook Upgrade
• Thunderstorms not expected to become severe
• Hazardous Winter Weather
• Heavy Rainfall
• FIRE WEATHER OUTLOOK
• Day 1 Day 2 Days 3-8
• OPERATIONAL FORECASTS ARE BOTH DETERMINISTIC AND
  PROBABILISTIC

Approximate
Growth Exp to 8 days
75 of all SPC products are valid for lt 24h
period
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SPC Approach to Ensembles

• Develop specialized guidance based on the
  particular hazardous weather application (severe
  wx, fire wx, winter wx)
• Design guidance to
• Support SPCs probabilistic forecast products
• Help blend deterministic and ensemble methods
• Use larger-scale environmental information to
  produce (downscaled) probabilistic guidance
• Provide decision support for high impact weather
• Properly gauge confidence
• Alert for rare but significant events

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CONVECTIVE OUTLOOKSCategorical and Probabilistic
Fcsts Operational through Day 3 Exp through Day
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Tornado (Hatched area 10 gt F2)
Categorical
Wind
Hail (Hatched area 10 gt 2)
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OPERATIONAL WATCH PROBABILITIES
Severe Thunderstorm Watch 688 Probability Table
Tornadoes Tornadoes
Probability of 2 or more tornadoes Low (10)
Probability of 1 or more strong (F2-F4) tornadoes Low (lt5)
Wind Wind
Probability of 10 or more severe wind events Mod (60)
Probability of 1 or more wind event gt 65 knots Low (10)
Hail Hail
Probability of 10 or more severe hail events Low (10)
Probability of 1 or more hailstones gt2 inches Low (lt5)
Combined Severe Hail/Wind Combined Severe Hail/Wind
Probability of 6 or more combined severe wind/hail events Mod (60)
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Experimental Enhanced Thunderstorms OutlooksTwo
periods (Division at 03Z 10, 40, and 70
intervals)
Probabilistic
Probabilistic
Thunderstorm Graphic valid until 3Z
Thunderstorm Graphic valid 3Z to 12Z
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General EnsembleGuidance Used Operationallyat
the SPC(SREF and MREF)
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Ensemble Mean
MREF 500 mb Mean Height Mean Temp Mean Wind
GFS Ensemble at SPC F216 valid 00 UTC 21 June
2006
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Ensemble Mean Spread
MREF 500 mb Mean Height SD Height
GFS Ensemble at SPC F216 valid 00 UTC 21 June
2006
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Another way to view uncertainty Spaghetti
MREF 500 mb 14 members CTRL HGHT (5760 m)
GFS Ensemble at SPC F216 valid 00 UTC 21 June
2006
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Ensemble Mean Departure from Normal
MREF 500 mb Mean Height Number of SD from normal
GFS Ensemble at SPC F216 valid 00 UTC 21 June
2006 (e.g., Grumm and Hart 2001)
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Ensemble Mean Normalized Variance
(Predictability RMOP also available)
MREF 500 mb Mean Height Normalized variance
GFS Ensemble at SPC F216 valid 00 UTC 21 June
2006
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Postage Stamps 500 mb HGHT
14 members CTRL
GFS Ensemble at SPC F216 valid 00 UTC 21 June
2006
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Postage Stamps Fosberg Index(Fosberg Index is
a measure of fire threat due to weather
conditions alone based on T, RH, and wind speed)
14 members CTRL
High Fosberg Index in a few members
GFS Ensemble at SPC F216 valid 00 UTC 21 June
2006
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Joint Probability (SREF)P(P12I lt .01) x P(V gt
20 mph) x P(RH lt 15) x P(T gt 60F)
Explore the parameter space supporting critical
fire weather conditions
SREF Surface Joint Probability
Short-Range Ensemble at SPC F027 valid 00 UTC 13
June 2006
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Joint Probability (SREF)P(MLCAPE gt 1000 J/kg) x
P(MLCL lt 1 km) x P(0-1 SRH gt 100 m2/s2) x
P(0-6 km Shear gt 40 kts) x P(C03I gt .01)
First Day 2 High Risk Severe Outlook
ever issued by the SPC
Explore the parameter space supporting strong or
violent tornadoes gt F2 Thompson et al. (2003)
First Day 2 High Risk Outlook Issued by the SPC
36h SREF Forecast Valid 21 UTC 7 April
2006 SigTor Combination and Mean PMSL, 10m Wind
Vectors
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Commonly Used Ensemble Statistics Products at
the SPC

• Mean, Median, Max, Min, Spread, Range, Exceedance
  Probabilities, Joint and Combined Probabilities
• Basic Weather Parameters (Temperature, Height,
  Wind, RH, etc.)
• Derived Weather Parameters (for Severe, Winter,
  and Fire Weather, e.g., CAPE, Fosberg, SigTor,
  etc.)

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Calibrated EnsembleGuidance Used
Operationallyat the SPC(Mostly SREF)
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Calibrated Guidance Productsat the SPC

• Use the larger-scale environmental forecasts to
  produce calibrated ensemble guidance specific to
  hazards of importance to the SPC
• Probability of Thunderstorms
• Probability of Severe Thunderstorms
• Probability of Snowfall Accumulation (HPC/SPC
  collaboration)

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Probability of Thunderstorms

• Calibration largely based on two parameters
• Probability (CPTP gt 1) and Probability (P03I gt
  .01)
• Frequentist approach over the previous year
• Computationally fast and adaptable updated
  weekly
• Distance wgting accounts for regionalization
• More details in Bright et al. (2005) available on
  SPC website
• Output at 3h, 12h, and 24h periods (F03 F87)

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Joint Probability (Assumed Independence)
P(CPTP gt 1) x P(Precip gt .01) 3 hr valid period
21 UTC 31 Aug to 00 UTC 01 Sept 2004
15h Forecast Ending 00 UTC 01 Sept
2004 Uncalibrated probability Solid/Filled
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Uncalibrated Reliability Joint Probability (5
Aug to 5 Nov 2004)
Frequency 0, 5, , 100
Perfect Forecast
No Skill
Climatology
P(CPTP gt 1) x P(P03I gt .01)
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Calibrated Ensemble Thunder Probability
3 hr valid period 21 UTC 31 Aug to 00 UTC 01
Sept 2004
15h Forecast Ending 00 UTC 01 Sept
2004 Calibrated probability Solid/Filled
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Calibrated Ensemble Thunder Probability
3 hr valid period 21 UTC 31 Aug to 00 UTC 01
Sept 2004
15h Forecast Ending 00 UTC 01 Sept
2004 Calibrated probability Solid/Filled NLDN
CG Strikes (Yellow )
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Calibrated Reliability (5 Aug to 5 Nov 2004)
Frequency 0, 5, , 100
Perfect Forecast
Perfect Forecast
No Skill
Climatology
No Skill
Calibrated Thunder Probability
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Probability of Severe Thunderstorms

• Calibration uses an ingredients based approach
• CAPE/SHEAR Organized updrafts
• CAPE/DCAPE Downdraft potential
• CAPE/500 mb Temps Cold core lows
• Calibrated thunderstorm guidance
• Frequentist approach over previous year
• Computationally fast and adaptable updated
  weekly
• More details in Bright et al. (2006) available on
  SPC website
• Output at 3h, 12h, and 24h periods (F03 F87)

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24h Probability of a Severe Thunderstorm
Shading begins at 15
SREF 24h calibrated probability of a severe
thunderstorm F027 Valid 12 UTC 11 May 2005 to 12
UTC 12 May 2005
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SVR WX ACTIVITY 12Z 11 May 2005 to 12Z 12 May,
2005 a Hail wWind tTornado
SREF 24h calibrated probability of a severe
thunderstorm F027 Valid 12 UTC 11 May 2005 to 12
UTC 12 May 2005
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Severe
Verification
Hail gt .75
Wind gt 50 kts
Tornado
21 UTC F039 24h forecasts from 15 April to 15
October 2005
ROC Area .86 Ave Hit 15 Ave Miss 3
(24h Fcst F39, 21Z only)
21 UTC SREF only
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Probability of Snow Accumulating on Roads (HPC)

• Calibration uses P(P03I), P(PTYPE), and two
  derived parameters
• Simple surface parameter, f(TPBL,Ts, Qnet rad
  flux)
• Parameter to estimate whether 3 snow melts in 3h
  
• Frequentist approach over previous two years
• MADIS road-state data serve as truth
• Output at 3h and 6h periods (F03 F87)
• Experimental!

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Example Calibrated Accumulations30h forecast
NCEP SREF 3h Probability of Road Accumulation
Valid 15 UTC 21 March 2006
Average March probability of accumulation
(2004-2005) is 20
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Calibrated Reliability of New Snow on Roads
All 3h forecasts (F03-F87) from 1 Oct 2005 - 30
April 2006
?
OBS FREQ ()
FORECAST () ?
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Storm-Scale Modeling

• Subject of the SPC/NSSL 2005 Spring Program
• 3 explicit WRF models allowed for the creation of
  a Poor persons ensemble
• WRF-ARW2 (2 km grid space OU/CAPS)
• WRF-ARW4 (4 km grid space NCAR)
• WRF-NMM (4.5 km grid space NCEP/EMC)
• Explicit convection allowing forecasts
• Interested in resolved storm-scale structures
• Initiation, Mode, Evolution, Decay

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WRF 2 to 4.5 km ForecastsValid F02426 May 2005
2 km ARW
4 km ARW
4.5 km NMM
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WRF 2 to 4.5 km ForecastsValid F02426 May 2005
2 km ARW 4 km ARW 4.5 km NMM
Spaghetti of automated supercell
detection circles indicate a supercell
identified within 25 miles All three WRF models
contribute information to the supercell forecast
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Storm-Scale EnsembleNOAA Hazadous Weather
Testbed (HWT) in Norman, OK

• 2007 Spring Experiment will continue 2005 work
• 15 April 2007 through 15 June 2007
• 2008 and 2009 will incorporate WRF-NMM and
  various upgrades
• Collaboration between SPC and NSSL
• OU/CAPS (NWC)
• NCEP partners AWC, EMC, HPC
• WFO Norman
• 10 members, 4 km explicit convection allowing,
  mixed physics WRFs (eastern 2/3 CONUS)
• 2 km high-resolution deterministic WRF to
  accompany ensemble
• Emphasis on small-scale, high-impact hazardous
  weather (e.g., supercell/updraft strength,
  convective mode coverage, QPF)
• Prototype for future NCEP regional SREF system

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Summary

• Ensembles used operationally as decision support
  tool for SPCs hazardous weather product suite
• Severe Weather Fire Weather Winter Weather
• Ongoing efforts include
• Continue to develop specialized calibration for
  high-impact events
• Enhance ensemble guidance for severe and fire
  weather programs in the Day 3 through Day 8 range
  (NAEFS MREF)
• HWT/Spring Experiment (2007-2009) Short-range,
  high resolution, explicit convection allowing WRF
  ensembles (Collaborative effort within NCEP and
  WFO Norman)

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Combined Prob-o-Grams (SREF Cntrl NV)
10 - CG LTG Strikes
Pcpn
Wind
Joint Prob
RH