Upcoming Changes in Winter Weather Operations at the Weather Prediction Center (WPC) Great Lakes Operational Meteorological Workshop Dan Petersen, Wallace Hogsett, Faye Barthold, Mike Bodner, and Keith Brill

 New ensemble membership of probabilistic snow/freezing rain forecasts for the season  Experimental winter weather ‘watch recommender’  Experimental Days 4-7 Winter Weather Forecasts Presentation Outline

32-member ensemble:  WPC deterministic forecast  21 Short Range Ensemble Forecast (SREF) members  GFS  Global Ensemble Forecast (GEFS) Mean, 5 GEFS members  ECMWF, ECMWF Ensemble Mean  Canadian Global (GDPS) snowfall/freezing rain forecasts Previous Models/Ensembles Used to Compose Snow/Ice Probability Forecasts

24 Hour Forecast Liquid Equivalent Precipitation Valid 12z 04 Mar 2014 SREF Mean 87 hr precipitation forecast (left), Climate Prediction Center Analysis of observed precipitation (right) ForecastObserved

GFS 84 hr forecast (left), Climate Prediction Center Analysis (right) 24 Hour Forecast Liquid Equivalent Precipitation Valid 12z 04 Mar 2014 ForecastObserved

ECMWF 84 hr forecast (left), analysis (right) 24 Hour Forecast Liquid Equivalent Precipitation Valid 12z 04 Mar 2014 ForecastObserved

NAM 84 hour forecast (left), Climate Prediction Center Analysis (right) 24 Hour Forecast Liquid Equivalent Precipitation Valid 12z 04 Mar 2014 ForecastObserved

Weather Prediction Center 24 Hour Probability of Snow 12z 03 Mar to 12z 04 Mar 2014 The SREF, NAM further north axis of QPF results in northward expansion of probabilities in PA/NJ/NY/southern New England)

Run to Run Changes result in lower forecast confidence-03 Mar SREF Forecast 6 hour precipitation valid 18z 03 Mar 2014 (15z run left, 09z run right) Later run (left) decreases precip across southern NY/New England

Run to Run Changes result in lower forecast confidence-17 Mar 2014 The high probability of QPF over PA/northern NJ/Long Island NY too high and not calibrated (courtesy Rich Grumm and Jeff Tongue) - 14 Mar runs of the SREF probability of 12.5 mm of precip Mar runs of the SREF probability of 12.5 mm of precip 03z cycle 14 Mar 09z cycle 14 Mar15z cycle 14 Mar 21z cycle 14 Mar09z cycle 15 Mar 09z cycle 16 Mar

Need to include more datasets has resulted in the addition of 25 ECMWF ensemble members For the season: 57-member ensemble including  WPC deterministic forecast *25 ECMWF Ensemble members (transition to 0.5 degree resolution during season)  21 SREF members  GFS  GEFS Mean, 5 GEFS members  ECMWF, ECMWF Ensemble Mean  Canadian Global (GDPS) snowfall/freezing rain forecasts Models/Ensembles Used to Compose Snow/Ice Probability Forecasts

 Goal: provide maps of where the snow/freezing rain accumulation probabilities of watch/warning criteria exceed 50 percent for use in watch decisions  Maps of 12/24 hour forecasts will be posted on password protected winter weather page season: Experimental Winter Weather ‘Watch Recommender’

Step #1 – Compute probability of exceeding snow/ice accumulation thresholds and compare to local warning criteria to determine the probability of exceeding watch/warning criteria Step #2 – If probability of exceeding watch/warning criteria ≥ 50%, area on map is highlighted Step #3 – Produce map summarizing where >50% probability of exceeding watch/warning criteria occurs at any time during the 3 day period Methodology += WPC Snow Probability 12-hr warning criteria Probability of exceeding warning criteria ≥ 50% ? Highlight areas of >50% on map

Example – 12 March 2014 Summary map-all areas where >50% chance of exceeding 12 hr criteria anytime during 72 hr period ending 00 UTC 3/15 Probability of exceeding 12-hr criteria ending 12Z 3/12 Probability of exceeding 12-hr criteria ending 12Z 3/13 Probability of exceeding 12-hr criteria ending 18Z 3/12 Probability of exceeding 12-hr criteria ending 06Z 3/13 Probability of exceeding 12-hr criteria ending 00Z 3/13 ‘Watch Recommender’ is a tool to assist in collaboration between WPC and WFOs

Example – 7 March 2014 Blue highlights where probability of exceeding 24 hr snowfall criteria>50% Red highlights areas where probability of exceeding 24 hr freezing rain criteria >50%

Experimental Days 4-7 Winter Weather Forecasts Forecast Components: WPC QPF and international ensembles WPC QPF-2 day QPF divided into 24 hour components WPC Day hr QPF Day 6 24-hr WPC QPF Day 7 24-hr WPC QPF

Experimental Days 4-7 Winter Weather Forecasts Forecast Components Probability of WPC QPF >=.10 Ensemble Probability of Frozen Precipitation Probability of Winter Precipitation > 0.10” Forecasters edited probability of winter precipitation for individual models/ ensemble members and means

Future Work Thermal Probability Fields for all 3 Guidance sets Expand precipitation type guidance to include all GEFS, ECENS and CMCE members Add ensemble QPF mean from other ensemble systems (ECMWF, Canadian) Multi-ensemble Precipitation Type GEFS ECMWFGEFS+ECMWF

Experimental Days 4-7 Winter Weather Forecasts 24 hr snow ending 00z 13 Mar

Examples of Experimental Days 4-7 Winter Weather Forecasts  Day 7 forecast verifying 00z 13 Mar 2014 Red contours WPC probability of 0.10” liquid equivalent frozen precipitation Color filled graphic observed liquid equivalent precipitation (scale on left)

Examples of Experimental Days 4-7 Winter Weather Forecasts  Day 6 forecast verifying 00z 13 Mar 2014 Red contours WPC probability of 0.10” liquid equivalent frozen precipitation Color filled graphic observed liquid equivalent precipitation (scale on left)

Examples of Experimental Days 4-7 Winter Weather Forecasts  Day 5 forecast verifying 00z 13 Mar 2014 Red contours WPC probability of 0.10” liquid equivalent frozen precipitation Color filled graphic observed liquid equivalent precipitation (scale on left)

Examples of Experimental Days 4-7 Winter Weather Forecasts  Day 4 forecast verifying 00z 13 Mar 2014 Red contours WPC probability of 0.10” liquid equivalent frozen precipitation Color filled graphic observed liquid equivalent precipitation (scale on left)

 Snow and ice accumulation probabilities have been updated to incorporate 25 members of the ECMWF ensemble  Winter Weather ‘Watch recommender’ has been developed to match watch/warning criteria and produces maps of locations where the probability of the criteria being exceeded is >50%  Initial testing of days 4-7 winter weather outlooks has begun and more testing is forthcoming for  Future: NWS proposal to expand winter weather desk to 24 hour/day operations Summary: WPC Winter Weather Desk Updates

Questions or Comments? WPC Forecast Operations Branch (301)

Future Improvements  Timing  Output from watch recommender currently available at the very end of each WWD shift  Warning Criteria  Currently using estimates for Western Region, much of Southern Region  Not accounting for terrain

Experimental Days 4-7 Winter Weather Forecasts Forecast Components Probability of WPC QPF >= 0.10” ● WPC 24-hr QPF is used as a mean The 24-hr QPF from each of the 20 GEFS members and 50 ECENS members are used as a variance to compute a cumulative distribution function (CDF) of the WPC QPF reaching or exceeding 0.10” (top right image) Probability of WPC QPF >=.10 Ensemble Probability of Frozen Precipitation Probability of Winter Precipitation > 0.10” Frozen Precipitation Component ● An ensemble probability of frozen precipitation is generated using the precipitation type fields for snow, sleet and freezing rain in each of the GEFS members (middle right image) ● Probability of winter precipitation >= 0.10” is derived from multiplying ensemble probability of frozen precipitation by the probability of the WPC QPF >= 0.10” (Bottom right image)

2014 NCEP Ensemble Users workshop: User_workshop.shtml SREF upgrade: am/pdf/S1-02-SREF2014.pdf am/pdf/S1-02-SREF2014.pdf ECMWF upgrade: am/pdf/S4-04-RB_2014_03_NCEP_WSensUsers.pdf QPF Object oriented verification: #page=page-1 Updates, Plans, and Applications

Impetus to Change Ensemble Membership in Probabilistic Snow Forecasts Analysis of Observed 24 Hr Snow ending 00z 04 Mar

Winter Weather Desk Forecast Snowfall Accumulation Ending 00z Tue 04 Mar 2014

72 Hr 50 th Percentile Snowfall ending 00z Tue 04 Mar 2014

DCA Forecast SREF mean snow 12.4 inches observed 7 inches observed

DCA Forecast experimental SREF mean snow 11.7 inches observed 7 inches observed

NAM B 84 hr forecast (left), Climate Prediction Center Analysis (right) 24 Hour Forecast Liquid Equivalent Precipitation Valid 12z 04 Mar 2014