Weather Prediction Center (WPC) Winter Weather Desk Operations Changes for 2017 - 2018 Season Dan Petersen Bruce Veenhuis Greg Carbin Mark Klein Mike Bodner February 23-25, 2017

Weather Prediction Center (WPC) Winter Weather Desk Operations Outline Describe changes in WPC snow & ice ensemble forecasts that go into Probabilistic Winter Precipitation Forecast generation (PWPF) Explain why there was a decrease in the models used in the forecast Explain changes in forecast generation and collaboration timelines Describe use of WPC Watch Collaborator and new interface Discuss 2016-17 forecast verification for snow

Winter Weather Desk Overview (Internal Content) http://www.wpc.ncep.noaa.gov/wwd/internal Deterministic 6-hour forecasts for snow/sleet & freezing rain Snow to liquid ratio grids & graphics Watch Collaborator maps and loops WPC/National Digital Forecast Database difference fields

Winter Weather Desk Overview (Public Content) http://www.wpc.ncep.noaa.gov/ 24-hr probabilities for snow/sleet & freezing rain computed from deterministic forecast and ensemble spread Days 4-7 probabilities for snow/sleet 0.25” Ensemble surface low tracks Heavy snow/freezing rain discussion      (QPFHSD)

2017-18 Changes to Probabilistic Snow & Ice Forecasts http://origin.wpc.ncep.noaa.gov/wwd/winter_wx.shtml

Snow Verification Roebber Performance Diagram Frequency Bias = High bias # of forecast events # of observed events Low bias

Roebber Performance Diagram Threat Score = Hits Hits + Misses + False Alarms

CONUS Snow Verification: Nov. 2016 - Jan 2017 Bias More Skill Based on CoCoRaHS and Coop snow Obs Case Count = 639379 Event Count = ~ 1290 SREF ARW ECMWF Ensembles

Improved Resolution and Snow Level Calculations Old - 70 Members New - 46 Members 90th Percentile Forecasts Valid: 12 UTC Feb. 7, 2017 (Arrows show higher resolution and use of snow level for each member leading to improved depiction of snow in terrain.)

Changes in Ensemble Membership The High Resolution Ensemble WRF-ARW member 2 - operational November 1, 2017 WRF ARW & NMMB arrive before the 00z/12z GFS arrives allowing 3 additional high resolution windows on day 1 forecast WPC probabilities will incorporate the last 2 cycles (00z and 12z) 3 members X 2 cycles = 6 members

Changes in Ensemble Membership Ensemble Membership (day shift example) Sept. 2016-May 2017 Nov. 2017 Changes in Ensemble Membership Ensemble Membership (day shift example)  6 SREF ARW (09z)  9 SREF NMMB (09z) 10 ECMWF Ensemble (00z) 10 GFS Ensemble Members (06z)  4 ARW Hires Window (00z/12z) Day 1 or GFS (06z)/SREF NMMB Day 2,3  2 NMB Hires Window (00z/12z) Day 1 or GFS (00z)/SREF NMMB Day 2,3  1 GFS 12z  1 ECMWF Deterministic (00z)  1 NAM Nest (Days 1-2) or NAM 12 km (Day 3) (12z)  1  GEFS Ensemble Mean (06z) 45 Total Members  1     WPC Deterministic 46 Total Members For PWPF 26 SREF (all ARW/NMMB members) 25 ECMWF Ensemble 00z (randomly chosen) 10 GFS Ensemble Members 06z 1 CMC 00z 1 ECMWF Ens Mean 00z 1 00Z ARW Hires Window (00z GFS on Day 2) 1 00Z NMMB Hires Window (06z GFS on Day 2) 1 GFS 12z 1 ECMWF Deterministic 00z 1 NAM Nest 12z (Day 1-2), NAM 12km Day 3 1 GEFS Ensemble Mean 06z 69 Total Members 1 WPC Deterministic 70 total members for PWPF

WPC Watch Collaborator Probability of Exceeding WFO Snow and Ice Watch Criteria NEW http://www.wpc.ncep.noaa.gov/wwd/internal/watchcollab/watch_collaborator.php

WPC Watch Collaborator Probability of Exceeding WFO Snow and Ice Watch Criteria Summary Graphic 30 percent probability occurring at least 1 time period Freezing rain criteria met Snow criteria met

WPC Watch Collaborator Probability of Exceeding WFO Snow and Ice Watch Criteria Loop of 24h freezing rain probabilities in 6-hr time steps. Jan. 15-16, 2017

WPC Watch Collaborator Probability of Exceeding WFO Snow and Ice Watch Criteria Loop of 24h snow probabilities in 6-hr time steps. Mar 14-16, 2017

WPC Forecast Operations 2017-18    Display of Trends in Watch Collaborator Probabilities (date to be announced) positive Increasing variance means less trust in trend. negative   Left: How many of the last 3 cycles have probabilities >=30 percent of exceeding watch criteria? Center: What is the trend (increasing or decreasing) over last 2 cycles of watch collaborator probabilities? Right: How much variance has there been in watch probabilities (magnitude of change)?

WPC Forecast Operations 2017-18     Ensemble Membership, November 2017 Day shift example 2045z Post Collaboration*        02z Update*  6 SREF ARW (09z)  9 SREF NMMB (09z) 10 GFS Ensemble Members (06z) 10 ECMWF Ensemble (00z)  1 GFS (12z)  1 NAM Nest (Days 1-2) or NAM (Day 3) (12z)  4 ARW Hires Window (00z/12z) Day 1 or GFS (06z)/SREF NMMB Day 2,3  2 NMB Hires Window (00z/12z) Day 1 or GFS (00z)/SREF NMMB Day 2,3  1 ECMWF Deterministic (00z)  1  GEFS Ensemble Mean (06z) 45 Total Members  1     WPC Deterministic 46 Total Members For PWPF * Add 12 hours for 0845z and 1400z Post Collaboration and Update times.  6 SREF ARW (21z)  9 SREF NMMB (21z) 10 GFS Ensemble Members (18z) 10 ECMWF Ensemble (12z)  1 GFS (18z)  1 NAM Nest (Days 1-2) or NAM (Day 3) (18z)  4 ARW Hires Window (00z/12z) Day 1 or GFS (12z)/SREF NMMB Day 2,3  2 NMB Hires Window (00z/12z) Day 1 or GFS (06z)/SREF NMMB Day 2,3  1 ECMWF Deterministic (12z)  1 GEFS Ensemble Mean (18z) 45 Total Members  1     WPC Deterministic 46 Total Members For PWPF

Winter Weather Desk - Day Shift Forecast Product Timeline         PWPF = Probabilistic Winter Precipitation Forecast Prelim PWPF and watch collaborator available Updated PWPF and watch collaborator available Final PWPF and watch collaborator available Post collaborated grids sent Deadline for deterministic snow/ice updates Prelim snow/ice grids sent   1730z 1800z 2015z 2045z 0100z 0200z WPC/WFO collaboration (chats,calls) Additional collaboration (event driven) No further collaboration (no sn/zr updates)

    WPC Deterministic Snow Verification      Day 1 Snow 2016-17 Over the CONUS https://www.nohrsc.noaa.gov/ Frequency bias  automated ensemble (green) vs. winter weather desk (red) Threat score automated ensemble (green) vs. winter weather desk (red) Automated Ensemble (WSE): NAM + GFS + ECMWF + SREF + GEFS + ECMWF* + WRF ARW + NMMB + Canadian Global * partial membership

    WPC Deterministic Snow Verification      Day 2 Snow 2016-17 Over the CONUS https://www.nohrsc.noaa.gov/ Frequency bias  automated ensemble (green) vs. winter weather desk (red) Threat score automated ensemble (green) vs. winter weather desk (red) Automated Ensemble (WSE): NAM + GFS + ECMWF + SREF + GEFS + ECMWF* + WRF ARW + NMMB + Canadian Global * partial membership

    WPC Deterministic Snow Verification      Day 3 Snow 2016-17 Over the CONUS https://www.nohrsc.noaa.gov/ Frequency bias  automated ensemble (green) vs. winter weather desk (red) Threat score automated ensemble (green) vs. winter weather desk (red) Automated Ensemble (WSE): NAM + GFS + ECMWF + SREF + GEFS + ECMWF* + WRF ARW + NMMB + Canadian Global * partial membership

Freezing Rain Case Verification 07-08 Feb 2017 Icing amounts higher than forecast across interior eastern NY and MA

WPC Winter Weather Desk Operations Summary of Changes Improvements in probabilistic products, with snow level calculation added and members run at 5 km resolution Reduced SREF ARW & ECMWF members for 2017-18 due to bias and resolution issues, respectively Number of high resolution window forecasts increases from 2 to 6 Watch Collaborator probabilities now updated by 14z/02z WPC deterministic forecasts now issued at 1730z and 0530z New Watch Collaborator trend tools maps coming soon Freezing rain accumulations verified using ASOS freezing rain sensor

Questions or Comments? Thank You! Winter Weather Desk (301)683-0784 Dan.Petersen@noaa.gov

Verification of Model/Ensemble Surface Low Forecasts

WPC Probability Forecast Verification Winter 2016-17 Snow Prob 4” Observed Frequency vs Predicted Probability Day 1 Day 2 Under forecast Over forecast