Weather Prediction Center WPC Winter Weather Desk Operations

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 = # of forecast events # of observed events s a i b h g i H b w o L s a i

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

CONUS Snow Verification: Nov. 2016 - Jan 2017 Bias More Skill Based on Co. Ra. HS 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 90 th 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 00 z/12 z GFS arrives allowing 3 additional high resolution windows on day 1 forecast • WPC probabilities will incorporate the last 2 cycles (00 z and 12 z) • 3 members X 2 cycles = 6 members

Changes in Ensemble Membership (day shift example) Sept. 2016 -May 2017 26 SREF (all ARW/NMMB members) 25 ECMWF Ensemble 00 z (randomly chosen) 10 GFS Ensemble Members 06 z 1 CMC 00 z 1 ECMWF Ens Mean 00 z 1 00 Z ARW Hires Window (00 z GFS on Day 2) 1 00 Z NMMB Hires Window (06 z GFS on Day 2) 1 GFS 12 z 1 ECMWF Deterministic 00 z 1 NAM Nest 12 z (Day 1 -2), NAM 12 km Day 3 1 GEFS Ensemble Mean 06 z 69 Total Members 1 WPC Deterministic 70 total members for PWPF Nov. 2017 6 SREF ARW (09 z) 9 SREF NMMB (09 z) 10 ECMWF Ensemble (00 z) 10 GFS Ensemble Members (06 z) 4 ARW Hires Window (00 z/12 z) Day 1 or GFS (06 z)/SREF NMMB Day 2, 3 2 NMB Hires Window (00 z/12 z) Day 1 or GFS (00 z)/SREF NMMB Day 2, 3 1 GFS 12 z 1 ECMWF Deterministic (00 z) 1 NAM Nest (Days 1 -2) or NAM 12 km (Day 3) (12 z) 1 GEFS Ensemble Mean (06 z) 45 Total Members 1 WPC Deterministic 46 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 24 h 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 24 h 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 2045 z Post Collaboration* 6 SREF ARW (09 z) 02 z Update* 6 SREF ARW (21 z) 9 SREF NMMB (09 z) 10 GFS Ensemble Members (06 z) 10 ECMWF Ensemble (00 z) 1 GFS (12 z) 1 NAM Nest (Days 1 -2) or NAM (Day 3) (12 z) 4 ARW Hires Window (00 z/12 z) Day 1 or GFS (06 z)/SREF NMMB Day 2, 3 2 NMB Hires Window (00 z/12 z) Day 1 or GFS (00 z)/SREF NMMB Day 2, 3 1 ECMWF Deterministic (00 z) 1 GEFS Ensemble Mean (06 z) 45 Total Members 9 SREF NMMB (21 z) 10 GFS Ensemble Members (18 z) 10 ECMWF Ensemble (12 z) 1 GFS (18 z) 1 NAM Nest (Days 1 -2) or NAM (Day 3) (18 z) 4 ARW Hires Window (00 z/12 z) Day 1 or GFS (12 z)/SREF NMMB Day 2, 3 2 NMB Hires Window (00 z/12 z) Day 1 or GFS (06 z)/SREF NMMB Day 2, 3 1 ECMWF Deterministic (12 z) 1 GEFS Ensemble Mean (18 z) 45 Total Members 1 WPC Deterministic 46 Total Members For PWPF * Add 12 hours for 0845 z and 1400 z Post Collaboration and Update times.

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

WPC Deterministic Snow Verification Day 1 Snow 2016 -17 Over the CONUS https: //www. nohrsc. noaa. gov/ Threat score automated ensemble (green) vs. winter weather desk (red) Frequency bias 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/ Threat score automated ensemble (green) vs. winter weather desk (red) Frequency bias 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/ Threat score automated ensemble (green) vs. winter weather desk (red) Frequency bias 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 14 z/02 z • WPC deterministic forecasts now issued at 1730 z and 0530 z • New Watch Collaborator trend tools maps coming soon • Freezing rain accumulations verified using ASOS freezing rain sensor

Thank You! Questions or Comments? • 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