SPC Ensemble Applications: Current Status and Future Plans

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1 : Current Status and Future Plans Israel Jirak Science Support Branch Storm Prediction Center Norman, OK Acknowledgments: Steve Weiss, Andy Dean, Gregg Grosshans, and Chris Melick

2 Outline Large-Scale Guidance: GEFS, NAEFS Extended Outlooks: Severe, Fire Mesoscale Guidance: SREF Overview, Calibrated Severe Storm-Scale Guidance: SSEF, SSEO Storm-Scale Ensemble Forecasts (SSEF) Overview, Variables, Calibrated Severe Storm-Scale Ensemble of Opportunity (SSEO) Concept, Examples

3 Large-Scale Guidance Forecasters utilize GEFS, NAEFS, and deterministic models to assess the large-scale pattern and its predictability Extended Range Outlooks Severe Weather Outlook Day 4-8 : 30% probability of severe w/in 25 mi of point Fire Weather Outlook Day 3-8: 70% probability of fire wx cond. w/in 12 mi of point Probabilistic Fire Weather Outlook Day 3-8: Adds marginal 40% probability area Plan to expand probabilistic forecasts to extended severe outlook, so likely an enhanced usage of GEFS/NAEFS Severe Day 4-8 Fire Day 3-8 4/27

4 Mesoscale Guidance 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

5 SPC Ensemble Applications Mesoscale Guidance: SREF Specialized guidance for the specific application (severe weather, fire weather, winter weather) Guidance designed to Help blend deterministic and ensemble approaches Provide guidance for uncertainty/probabilistic forecasts Provide guidance that aids (deterministic) confidence Illustrate a range of plausible scenarios Allow for diagnostic analysis - not just a statistical black-box Facilitate extensive use of probabilistic products Recent developments/improvements include 1-hr, 4-hr, & 8-hr calibrated thunder probabilities for year-round enhanced thunder product

6 Mesoscale Guidance: SREF Calibrated Severe Provide guidance to forecasters when making probability forecasts of severe weather Currently products are calibrated against all severe reports Plan to calibrate for each type of severe hazard (tornado, wind, and hail), which is challenging due to the nature of the severe report database Day 1 Outlook already broken down by individual hazard Goal is to produce higher temporal resolution severe outlooks (e.g. 4-hr periods), so reliable guidance will be critical 1630Z Day 1 Convective Outlook (4/27/2011) tornado wind hail

7 SPC Ensemble Applications Mesoscale Guidance: SREF Calibrated Severe Four-level classification based on environment: 1) large CAPE/strong shear (based on SCP) - supercell 2) moderate CAPE/moderate shear - multicell 3) large CAPE/weak shear - ordinary/pulse 4) marginal CAPE/strong shear - cool season/shallow These probabilities (e.g., probability of SCP>1) are paired with SREF calibrated probability of thunderstorms. The probabilities are then binned and associated with an historical frequency of severe weather within 25 miles of a point. 3-hr SREF Calibrated Severe

8 Storm-Scale Guidance: SSEF A lack of observational sampling, scientific understanding, and ability to resolve small-scale features related to thunderstorm development necessitates the use of storm-scale ensembles in severe weather forecasting Experimental Storm-Scale Ensemble Forecast (SSEF) system has been produced for the NOAA Hazardous Weather Testbed (HWT) Spring Experiment by OU/CAPS for the past 5 years Comprised of 4-km convection-allowing WRF and ARPS members: members; members; members; members (full CONUS out to 30 h); members (full CONUS out to 36 h) At 4-km horizontal grid spacing, these models explicitly produce deep convection and provide valuable information on convective mode (i.e., supercell vs. quasi-linear system) and possible intensity/severity of storms Primarily interested in storm-attribute fields, especially hourly maximum fields (HMFs) HMFs examined: Updraft Helicity, which represents a rotating updraft in a simulated storm Updraft/Downdraft Speed 10-m AGL Wind Speed to identify convective gusts 1-km AGL Simulated Reflectivity

9 Storm-Scale Guidance: SSEF Traditional ensemble probabilities of HMFs from high-resolution models are not especially useful, owing to poor agreement among members at the grid point of these fields. Applying a binary neighborhood approach to a storm-scale ensemble improves the statistical results of HMFs in forecasting severe weather ROI=20-40 km Sigma=30 grid points 03 May 2008 (Harless 2010)

10 Mesoscale Guidance: SSEF Calibrated Severe Three-level classification based on storm attributes: 1) updraft helicity - supercell 2) updraft speed multicell, ordinary/pulse 3) 10-m wind speed bow echo/mcs Improved statistical results over SREF during SE hr SREF Calibrated Severe 3-hr SSEF Calibrated Severe

11 Storm-Scale Guidance: SSEO While an operational ensemble of convection-allowing models (CAMs) like the SSEF may not be available for some time, SPC is exploring the utility of blending existing CAMs into a storm-scale ensemble of opportunity (SSEO) Advantages: Data already available onsite Efficient method of summarizing data from multiple deterministic models Data available year round, which would allow for a large sample for calibration purposes Disadvantages: Little to no control over configuration Likely insufficient diversity

12 Storm-Scale Guidance: SSEO Members 1) NSSL WRF-ARW 2) HRW WRF-ARW 3) HRW WRF-ARW -12 h 4) EMC WRF-NMM 5) HRW WRF-NMM 6) HRW WRF-NMM -12 h 7) NMMB Nest

13 Storm-Scale Guidance: SSEO Products Using built-in ensemble functions in N- AWIPS/GEMPAK to minimize post-processing Ensemble products include Ensemble mean Ensemble max Percentile values Traditional ensemble probability grid point) Smoothed traditional ensemble probability Binary neighborhood ensemble probability code written locally to calculate neighborhood maxima Smoothed binary neighborhood ensemble probability

14 Storm-Scale Guidance: SSEO Example HM Updraft Helicity > 25 m 2 s -2 SSEO 24-hr fcst valid 00Z 28 April

15 Storm-Scale Guidance: SSEO Example Ensemble Maximum HM Updraft Helicity (m 2 s -2 ) SSEO 24-hr fcst valid 00Z 28 April

16 Storm-Scale Guidance: SSEO Example 40-km Neighborhood Probability HM Updraft Helicity >25 m 2 s -2 SSEO 24-hr fcst valid 00Z 28 April

17 Storm-Scale Guidance: SSEO Example 40-km Neighborhood Smoothed Prob HM Updraft Helicity >25 m 2 s -2 SSEO 24-hr fcst valid 00Z 28 April

18 Storm-Scale Guidance: SSEO Example 3-hr Ensemble Maximum HM Updraft Helicity (m 2 s -2 ) SSEO 24-hr fcst valid 00Z 28 April

19 Storm-Scale Guidance: SSEO Example 40-km Neighborhood 3-hr Smoothed Prob HM Updraft Helicity >25 m 2 s -2 SSEO 24-hr fcst valid 00Z 28 April

20 Storm-Scale Guidance: SSEO Example Preliminary Severe Storm Reports 21Z 03Z 40-km Neighborhood 3-hr Smoothed Prob HM Updraft Helicity >25 m 2 s -2 SSEO 24-hr fcst valid 00Z 28 April

21 Storm-Scale Guidance: SSEO Example Preliminary Severe Storm Reports 21Z 03Z 40-km Neighborhood 3-hr Smoothed Prob HM Updraft Helicity >25 m 2 s -2 SSEO 27-hr fcst valid 03Z 28 April

22 Summary Large-Scale Guidance: GEFS, NAEFS Looking to expand the role of GEFS/NAEFS in the extended outlook process, especially moving toward extended probabilistic severe outlooks Mesoscale Guidance: SREF Continue to develop and improve environment-based calibrated products from the SREF including severe products with increased temporal resolution that are broken down by severe type Storm-Scale Guidance: SSEF, SSEO The future of severe weather forecasting depends on storm-scale ensembles The HWT Spring Experiment plays an important role in cultivating ideas and techniques for this next-generation ensemble Assess the utility of the SSEO in severe weather forecasting Develop storm attribute-based calibrated products from the SSEF & SSEO