1. 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

2. 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 forecast verification for snow

3. Winter Weather Desk Overview (Internal Content)
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

4. Winter Weather Desk Overview (Public Content)
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)

5. 2017-18 Changes to Probabilistic Snow & Ice Forecasts

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

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

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

9. 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.)

10. 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

11. Changes in Ensemble Membership Ensemble Membership (day shift example)
Sept May 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

12. WPC Watch Collaborator Probability of Exceeding WFO Snow and Ice Watch Criteria
NEW

13. 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

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

15. 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

16. 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)?

17. 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

18. 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)

19.     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

20.     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

21.     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

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

23. 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 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

24. Questions or Comments? Thank You! Winter Weather Desk (301)683-0784

25. Verification of Model/Ensemble Surface Low Forecasts

26. WPC Probability Forecast Verification Winter Snow Prob 4” Observed Frequency vs Predicted Probability
Day 1
Day 2
Under forecast
Over forecast