Upcoming Changes in Winter Weather Operations at the
Weather Prediction Center (WPC)
Great Lakes Operational Meteorological WorkshopDan Petersen, Wallace Hogsett, Faye Barthold,
Mike Bodner, and Keith Brill
New ensemble membership of probabilistic snow/freezing rain forecasts for the 2014-15 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)
Forecast
Observed
GFS 84 hr forecast (left), Climate Prediction Center Analysis (right)
24 Hour Forecast Liquid Equivalent Precipitation Valid 12z 04 Mar 2014
Forecast
Observed
ECMWF 84 hr forecast (left), analysis (right)
24 Hour Forecast Liquid Equivalent Precipitation Valid 12z 04 Mar 2014
Forecast
Observed
NAM 84 hour forecast (left), Climate Prediction Center Analysis (right)
24 Hour Forecast Liquid Equivalent Precipitation Valid 12z 04 Mar 2014
Forecast
Observed
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 2014
http://eyewall.met.psu.edu/rich/compare/
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
- 14-16 Mar runs of the SREF probability of 12.5 mm of precip
03z cycle 14 Mar
09z cycle 14 Mar
15z cycle 14 Mar
21z cycle 14 Mar
09z cycle 15 Mar
09z cycle 16 Mar
Need to include more datasets has resulted in the addition of 25 ECMWF ensemble membersFor the 2014-15 season: 57-member ensemble including WPC deterministic forecast* 25 ECMWF Ensemble members (transition to 0.5 degree
resolution during 2014-15 season) 21 SREF members GFS GEFS Mean, 5 GEFS members ECMWF, ECMWF Ensemble Mean Canadian Global (GDPS) snowfall/freezing rain
forecasts
2014-15 Models/Ensembles Used to Compose Snow/Ice Probability Forecasts
http://www.wpc.ncep.noaa.gov/pwpf/about_pwpf_products.shtml
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
2014-15 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
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 6-7 48-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 • 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 ECMWF GEFS+ECMWF
Experimental Days 4-7 Winter Weather Forecasts
24 hr snow ending 00z 13 Mar 2014 www.nohrsc.noaa.gov
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 2014-15
Future: NWS proposal to expand winter weather desk to 24 hour/day operations
Summary: WPC Winter Weather Desk Updates
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 ComponentsProbability of WPC QPF >= 0.10”●WPC 24-hr QPF is used as a meanThe 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 isgenerated 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:http://www.emc.ncep.noaa.gov/gmb/ens/WkShopOct13/6th_User_workshop.shtmlSREF upgrade: http://www.emc.ncep.noaa.gov/gmb/ens/WkShopOct13/program/pdf/S1-02-SREF2014.pdfECMWF upgrade:http://www.emc.ncep.noaa.gov/gmb/ens/WkShopOct13/program/pdf/S4-04-RB_2014_03_NCEP_WSensUsers.pdfQPF Object oriented verification: http://www.wpc.ncep.noaa.gov/verification/mode/mode.php#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 2014
http://www.nohrsc.noaa.gov
Winter Weather Desk Forecast Snowfall Accumulation Ending 00z
Tue 04 Mar 2014
72 Hr 50th 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
http://www.srh.noaa.gov/ridge2/snow/index.php?site=dtx