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MDL User Group Meeting on Severe Weather Technology for NWS Warning Decision Making

BRIDGING THE GAP BETWEEN SEVERE WEATHER WATCHES AND WARNINGS Steven J. Weiss steven.j.weiss@noaa.gov. MDL User Group Meeting on Severe Weather Technology for NWS Warning Decision Making July 11-14, 2005 Silver Spring, MD. Where Americas Climate and Weather Services Begin. Outline.

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MDL User Group Meeting on Severe Weather Technology for NWS Warning Decision Making

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  1. BRIDGING THE GAP BETWEEN SEVERE WEATHER WATCHES AND WARNINGSSteven J. Weisssteven.j.weiss@noaa.gov MDL User Group Meeting on Severe Weather Technology for NWS Warning Decision Making July 11-14, 2005 Silver Spring, MD Where Americas Climate and Weather Services Begin

  2. Outline • Severe Thunderstorm Forecasting • Role of the environment in assessment of storm potential • Sampling and resolution issues • Use of models to supplement observational data • Eta and RUC Errors (especially PBL and instability) • Sensitivity of convection to environment details • Observed storms and convective mode • Modeled storms • WRF, cloud models, and high resolution ensembles • Verification of high resolution models • Summary of analysis and prediction limitations • Some requirements that may result in improved short-term forecasting of severe thunderstorms

  3. Synergy Between Severe Weather Forecasting and Warning • Correct anticipation of what to expect: • Reduces “surprise” events • Allows timely implementation of office severe weather plans • Enhanced Staffing Levels and Delegation of Duties • Collaboration with EMs / Media / Spotter Deployment, etc. • Leads to more confidence when issuing warnings • Use of appropriate radar interrogation strategies • Fosters increased lead time • Summary: accurate forecasts can result in better warnings and improved public service

  4. Some Differences Between Severe Weather Forecasting and Warning • Detection (warning) of existing severe weather is not the same as prediction (forecasting) of future occurrence or evolution • Warnings have improved because of advances in: • Technology (NEXRAD & AWIPS / WDSSII) • Science (Understanding of storm structure/processes) • Forecaster training and education • Delivery systems to the public • But analogous technological advancement for severe weather prediction has not yet occurred • Considerable uncertainty can exist in both the prediction and detection phases

  5. Modified Forecast Funnel • SPC focuses on relationship between synoptic - mesoscale environment and subsequent thunderstorm development and evolution • Must maintain awareness of mesoscale - synoptic scale interactions • Severe weather events occur on scales smaller than standard observational data (and typical model data) • The real atmosphere is more important than a model atmosphere

  6. Severe Thunderstorm Forecasting • Assessment of convective potential is often limited by insufficient sampling on the mesoscale in time and space (especially 3D water vapor) • Radiosondes • High vertical resolution, poor time and space resolution • Surface METARS • High horizontal and time resolution, no vertical information • Wind profilers and VAD winds • High vertical and time resolution, moderate horizontal res. • No thermodynamic data • Satellite retrievals (winds and thermodynamic) • Mod./high horizontal and time resolution, poor vertical res. • GPS Integrated Water Vapor • High time res., mod./high horizontal res., poor vertical res.

  7. The Link Between Observable Scales and Stormscale is not Necessarily Clear Observable scales Stormscale

  8. Severe Weather Forecasting • Key premise - We must use our (incomplete) knowledge of the environment and convective processes to determine the spectrum of storms that are possible, where & when they may occur, and how they may evolve over time

  9. Severe Thunderstorm Forecasting • We utilize NWP model output to supplement the limited sampling of real atmosphere (e.g., Eta and RUC output) • Model output forms the foundation for most SPC outlooks, and it also impacts watch decisions • But accounting for uncertainties in IC’s (inadequate sampling) and model physics errors is not easy • Example: Eta forecast soundings exhibit characteristic errors caused by: • Early / late activation of deep convection • Shallow convective scheme in BMJ

  10. Impact of Eta Model Deep Convection on Forecasts of CAPE Eta 24 hr forecast valid 12z 8 Nov 2000 3 hr Conv Pcpn CAPE

  11. Impact of Eta Model Deep Convection on Forecasts of CAPE Verifying Data 12z 8 Nov 2000 Radar Reflectivity CAPE

  12. Impact of Eta Model Deep Convection on Forecast Soundings Observed LCH Sounding 12z 8 Nov 24 hr Eta Fcst Valid 12z 8 Nov MUCAPE 929 J/kg Mean RH 75% MUCAPE 2634 J/kg Mean RH 28%

  13. Impact of Eta BMJ Shallow Convection Observed Verifying Sounding(Red/Green)and 12 hr Eta Fcst(Purple)

  14. Short-Term Severe Thunderstorm Environmental Parameter Guidance • Hourly Update Information on 3D Convective Parameters is routinely available • LAPS in AWIPS • MSAS/RSAS in AWIPS • SPC Mesoscale Analysis Web Page • All utilize observational data blended with model data for atmosphere above the ground

  15. Use of Objective Parameter Guidance • The availability of hourly 3D guidance fields can improve our situational awareness prior to and during severe weather episodes • In many instances, it provides very useful diagnostic guidance for severe weather forecasting • It can help us “recover” from inaccurate mesoscale model guidance (outlook products) • But, it can also give us a false sense of security • We must be cautious in treating these hourly fields as if they are actual observational data • Short-term model input can and will have errors in key fields (e.g., PBL structure)

  16. April 20, 2004 Challenges in Sfc Data Assim. and Fcstg PBL Evolution 34 Tornadoes Including One F3 8 Deaths, 21 Inj., $19 Million in Damage Jim Krancic

  17. 12z Eta Model Guidance

  18. 12 hr Eta Model 500 mb ForecastsValid 00z 21 Apr 04 Height and Vorticity Height, Temperature, Wind

  19. 12 hr Eta Model 850 mb and Sfc ForecastsValid 00z 21 Apr 04 850 mb Height,Temperature, Wind MSLP Isobars, 2m Dewpoint

  20. 12 hr Eta CAPE/Shear/SRH ForecastsValid 00z 21 Apr 04 MLCAPE/SHR6/SRH3 MUCAPE/SHR6/SRH3

  21. 12 hr Eta 3h Accum. Pcpn/VV ForecastValid 00z 21 Apr 04

  22. 15 hr Eta 3h Accum. Pcpn/VV ForecastValid 03z 21 Apr 04

  23. 18 hr Eta 3h Accum. Pcpn/VV ForecastValid 06z 21 Apr 04

  24. 6 hr Eta PFC for Peoria, IL (PIA)Valid 18z 20 Apr 04

  25. 9 hr Eta PFC for Peoria, IL (PIA)Valid 21z 20 Apr 04

  26. 12 hr Eta PFC for Peoria, IL (PIA)Valid 00z 21 Apr 04

  27. 12z RUC Model Guidance

  28. 12 hr RUC ForecastsValid 00z 21 Apr 04 MSLP Isobars and 2m Dewpoint CAPE/SHR6/SRH3

  29. 12 hr RUC 3h Accum. Pcpn/VV ForecastValid 00z 21 Apr 04

  30. 6 hr RUC PFC for Peoria, IL (PIA)Valid 18z 20 Apr 04

  31. 9 hr RUC PFC for Peoria, IL (PIA)Valid 21z 20 Apr 04

  32. 12 hr RUC PFC for Peoria, IL (PIA)Valid 00z 21 Apr 04

  33. SPC Meso Analysis 21z 100 mb MLCAPE and MUCAPE

  34. 21z Radar and MLCAPE

  35. 21z Radar and MUCAPE

  36. CAPE Assessment • To diagnose differences between MLCAPE and MUCAPE, examination of hourly RUC soundings and surface data are required • SPC Meso Analysis combines hourly surface data with 1-hr forecasts from the previous hour RUC that provide environment information above the ground • For example, the 21z analysis incorporates 21z METAR data with a 1-hr forecast from the 20z RUC

  37. 1 hr RUC PFC for Peoria, IL (PIA)Modified with Observed T/TdValid 19z 20 Apr 04

  38. 1 hr RUC PFC for Peoria, IL (PIA)Modified with Observed T/TdValid 20z 20 Apr 04

  39. 1 hr RUC PFC for Peoria, IL (PIA)Modified with Observed T/TdValid 21z 20 Apr 04

  40. 1 hr RUC PFC for Peoria, IL (PIA)Modified with Observed T/TdValid 22z 20 Apr 04

  41. Meso Analysis Summary of CAPE • Looking at hourly RUC 1-hr forecast soundings at PIA as warm front lifted north of PIA indicates • Observed surface dew points did not blend well with model PBL background field from 1-hr forecast • Dry layer immediately above model ground during 20-22z period limited MLCAPE values to < 200 J/kg

  42. RUC Model Upgrade in 2004 • The RUC was upgraded in September 2004 • One change was designed to increase the vertical impact of observed surface T/Td data on model PBL profiles • The RUC PBL-based data assimilation should result in more accurate T/Td profiles in low levels • This should improve RUC hourly analyses • Better PBL profiles should result in improved short-term forecasts (including PFCs and 1-hr forecasts that feed the Meso Analyses) • Let’s examine RUC soundings for a January 2005 case

  43. SPC Meso Analysis 21z MLCAPE and MUCAPE

  44. 21z Radar and MLCAPE

  45. 21z Radar and MUCAPE

  46. RUC Soundings at Slidell 20-00z

  47. 1 hr RUC PFC for Slidell (6RO)Modified with Observed T/TdValid 20z 7 Jan 05

  48. 1 hr RUC PFC for Slidell (6RO)Modified with Observed T/TdValid 21z 7 Jan 05

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