Weather Prediction Center (WPC) Winter Weather Desk Operations Dan Petersen, Mike Bodner, Mark Klein, Chris Bailey, Dave Novak

Outline of Webinar Winter Weather Desk(WWD) operational 24 hours/day Collaboration of Quantitative Precipitation Forecasts (QPF) with the Winter Weather Forecast Changes to Winter Weather Watch Collaboration Tool Updates to Days 1-3 Probabilistic Snow/Ice Forecasts Change to Experimental Days 4-7 Winter Forecasts Forecast Verification

WPC Winter Weather Forecast Process Uses model/ensemble blender to generate first guess snow and freezing rain amounts -Dominant Precip Type Method for NCEP guidance -Thermal profile algorithm for non-NCEP guidance (ECMWF, UKMET, CMC) Model/ensemble precipitation type Quantitative Precipitation (now only WPC QPF allowed)

Winter Weather Desk Changes Workflow -24x7 operations -Day 1-3 forecasts due at 1815 Z(day) 0615Z (night) -Issue QPF earlier to integrate into winter forecasts Datasets -2.5 km Probabilistic Winter Forecasts going on Satellite Broadcast Network (SBN) -Planning to Revise Snow to Liquid Ratio forecasts Collaboration -Adopt collaboration call guidelines -Watch collaborator enhancements New Science-Testing use of microphysics-based algorithms

WWD Workflow: New Deadlines 06 UTC 0830 UTC 18 UTC 2030 UTC Collaboration Day 1-3 QPF and Winter Wx Updated Day 1-3 QPF and Winter Wx Day 1-3 QPF and Winter Wx Updated Day 1-3 QPF and Winter Wx OLDNEWCHANGE Day 1QPF WWD h later Day 2QPF WWD min later Day 3QPF h earlier WWD Changes in deadlines for 18 UTC cycle for WFOs * *Times shifted 12 hours for 06 UTC cycle Alert field of major changes Alert field of major changes Constant meteorological watch Unscheduled updates

The Snow/Ice Probabilistic Forecast GRIB2 files will be sent over the Satellite Broadcast Network starting November 16, 2015 (and still available on WPC’s ftp server) - working toward baselining in AWIPS 2 for next season Probability/percentile forecasts of snowfall and freezing rain over the contiguous US in 12, 24, 48 and 72- hour increments Winter Weather Desk Data Sets

Probabilistic Winter Precipitation Forecast Ensemble Composition (day shift) 63 members total (up from 58 members last season) 26 SREF members (21 during season, 09z) 25 ECMWF ensemble members, randomly selected (00Z) 1 NAM operational run (12Z) 1 GFS operational run (12Z) 1 ECMWF operational run (00Z) 1 Canadian Global Model (CMC) operational run (00Z) 1 ECMWF ensemble mean (00Z) 1 GFS ensemble mean (06Z) 5 GFS ensemble members, randomly selected (06Z) WPC deterministic forecast

Probabilistic Winter Precipitation Forecast (PWPF) Changes for PWPF snow and ice forecasts PRISM downscaled from 20 km to 2.5km resolution New products  Probability of snow >=.1”  5 th, 25 th, 75 th, and 95 th percentile accumulations of snow and ice (Provides a more complete Probability Distribution Function) Recreate PWPF suite for updates to deterministic forecasts

20km resolution vs 2.5km PRISM-downscaled 24-hour probability of snow ≥ 1”

Winter Weather Watch Collaborator Forecasts of probability of exceeding WFO watch/warning criteria, with summary maps where probabilities exceeded 50 percent

Add a new 30% contour in winter watch collaborator snow/ice graphics We will show both a 30 percent contour and 50 percent probability of exceeding 12/24 hour winter storm watch criteria Winter Weather Watch Collaborator Changes 24 hour winter storm watch criteria for snow(in)

Forecast Components: Probability of WPC QPF >=.25 “(last year 0.10”) Ensemble Probability of Snow/Ice Pellets Probability of Snow/Ice Pellets > 0.25” (last year 0.10”) Days 4-7 Probability Forecasts

Future Work Thermal Probability Fields for all 3 Guidance sets Determination of precipitation type includes all GEFS, ECENS and CMCE members Average of GEFS + ECENS + CMCE ensemble mean QPFs used to disaggregate of Day 4-5 and Day 6-7 WPC QPF GEFS+ECMWF+CMC ensembles Days 4-7 Probability Forecasts and Methodology

Days 4-7 Probability Forecasts Probability of exceeding 0.25” of combined snow/sleet as of December 1, 2015 (public)

Change in WPC default snow to liquid ratio (SLR) calculation The fraction of frozen precipitation x 10:1 SLR had highest threat score the past 2 seasons Higher riming plus lower fraction of frozen precipitation reduces snow ratios in mixed precipitation zones. Consequently, the WPC SLR blend plans to change for Snow to Liquid Ratio Method: NAM Roebber + GFS Roebber + Baxter Climatology + 11:1 Planned Snow to Liquid Ratio Method: NAM Rime Factor Roebber + NAM Rime Factor Baxter Climatology + GFS Roebber + Baxter Climatology + 11:1

WPC Winter Weather Forecast Verification

Operational NOHRSC Snowfall Analysis (V1) -poor quality in data sparse areas and terrain Relies on snowfall reports and not other observed precipitation. Improvements to gridded NOHRSC snowfall analysis will integrate QPE and use of HRRR model snow forecast Improving Collaboration and Verification: Common Analyses Season January Snowstorm Development NOHRSC

WPC Deterministic Snow Verification Day One Snow Threat Score Over the CONUS (NOHRSC analysis Final forecasts improved upon the Automated Ensemble for 4, 8, and 12” Automated Ensemble: NAM + GFS + ECMWF + SREF members + GEFS members + ECMWF members Better

WPC Deterministic Snow Verification Both automated consensus and human final forecasts have a high bias, especially for 12” Day One Snow Frequency Bias Over the CONUS (NOHRSC analysis ) Perfect

Summary Winter Weather Desk (WWD) operational 24 hours/day Days 1-3 Quantitative Precipitation Forecasts available along with the Winter Weather Forecast by 1815/0615 UTC Winter Weather Watch Collaborator expanded to include 30 & 50 percent probability of exceeding watch criteria Days 1-3 Probabilistic Snow/Ice Forecasts over SBN starting November 16 Experimental Days 4-7 Forecasts to be issued to public Deterministic Snow Verification shows improvement over automated ensemble, but with high bias

Questions or Comments? WPC Forecast Operations Branch (301) (Winter Weather) (301) (QPF, Lead Forecaster) Background slides: Days 2-3 Verification Low tracks verification Summary of Collaboration with Weather Forecast Offices

Low Tracks Verification ECMWF lowest distance error for low positions amongst models hours, GFS+ ECMWF blend for combination of models

WPC Deterministic Snowfall Forecast Day Two Snow Threat Score Over the CONUS (NOHRSC Analysis) Final forecasts outperform the Automated Ensemble for 4, 8, and 12 inches Better

WPC Deterministic Snowfall Forecast Final forecasts have a high bias, especially for 12” Day Two Snow Frequency Bias Over the CONUS Perfect

WPC Deterministic Snowfall Forecast Final forecasts outperform the Automated Ensemble for 4, 8, and 12” forecasts Day Three Snow Threat Score Over the CONUS Better

WPC Deterministic Snowfall Forecast Final forecasts have a high bias, especially for 12” Bias may be associated with snow analysis problems (bias higher than verification from WPC snow analysis) Day Three Snow Frequency Bias Over the CONUS Perfect

he Workflow: Winter Weather Desk now operational 24 hours, 7 days a week Provide unscheduled updates to deterministic and probabilistic forecasts until 03z for day shift forecasts and 15z for night shift forecasts Winter Weather Desk Operational Changes

WFO/WPC Collaboration by Year Record number of 12Planet questions, comments, and phone calls in the winter season!

Collaboration Call Protocols  Develop decision support messaging (which area is under greatest threat of heavy snow/freezing rain?)  Calls coordinated through Regional Operations Centers (ROC)  Either WFO or WPC can propose a call if ROC unavailable  Focus on addressing forecast differences or how to resolve guidance changes  2 nd WPC Winter forecaster available for collaboration UTC Winter Weather Desk Collaboration

Central Region WPC Winter Weather Desk Collaboration (Sept. 15, 2014 – May 15, 2015 ) Eastern Region Southern Region Western Region

WFO- WPC WWD Collaboration Winter 2014 – 2015) A Record Season! 419 questions from WFOs via 12Planet. –165 questions more than the winter season or a 65% increase from last winter. In fact, this is the highest total and largest amount of questions asked within an entire season. 75 direct telephone calls from WFOs. –An increase of a dozen from the year before, 63 in Conference Calls involving a total of 318+ known WFOs and all 4 Regions. –A dramatic increase, 18 total the prior four years. 360 times WFOs mentioned WWD graphics within 12Planet. –173 more than or a 93% increase and most since season (285).

Eastern Region 210 questions through 12Planet. (52% increase from last year) –1) BOX – 43 times –2) PHI – 27 –3) OKX – 22 –4) LWX – 16 –5) ALY and BTV – 13 –6) AKQ – 12 –7) BGM and GYX – 8 62 telephone calls from WFOs. (22% increase from last year) –1) LWX – 31 times –2) PHI – 13 –3) BOX – 8 17 Conference Calls with ER.

Central Region 142 questions through 12Planet. (78% increase from last year) - 1) ARX – ) MKX – 9 - 3) OAX – 8 - 4) LOT, LSX and SGF – 7 8 telephone calls from WFOs and 17 conference calls with CR.

Southern Region 54 question through 12Planet. (93% increase from last year) -1) FFC and MEG – 6 -2) LZK – 5 -3) MRX and TSA – 4 4 telephone calls from WFOs and 10 conference calls with SR.

Western Region 13 questions through12Planet. (63% increase from last yr.) –1) BYZ – 5 –2) TFX – 3 1 telephone call from WFOs and 1 conference call with WR.

Converting model snow into accumulation We’re gradually moving towards providing model-derived accumulations NAM model Rime Factor and fraction of frozen precipitation

NAM Percent of frozen precipitation and rime factor Rime Factor Percent of frozen precipitation

NAM Microphysics Riming Factor Variable density for precipitation ice (snow/graupel/sleet) – “riming factor”

% of frz pcp Shows transition Away from all Snow to mixed types as probability of frozen precip drops in eastern and southern MD

Mix on east side of DC at 21z Turning to snow by 00z 00z 13 Feb 2014 NAM Nest

NAM Snowfall Calculation Input fields: A = hourly accumulated QPF B = % frozen precipitation (hourly, instantaneous) C = Function of Rime factor (below; hourly, instantaneous) D = SLR from Roebber et al. (hourly, instantaneous) Accumulated snow/graupel/sleet = A*B*C*D, where C= 1.0 if 1<RF<2 D 0.5 if 2<RF<5 Varying 0.25 if 5<RF<20 Snow to Higher Rime Factor reduces snow to 0.17 if RF>20 Liquid Ratio Higher Rime Factor reduces snow to Liquid ratio and accumulation

Varying SLR (Uses RF) Valid: 06Z/27 Units: inches Differences (bottom left-top left) Constant SLR (RF not used) Constant SLR (RF not used) ●Bottom left plot uses a 10:1 SLR for the entire region shown ●The varying SLR approach reduced the accumulated snow/ice by as much as 3 inches in some places and more than 1 inch over a large region. ●The varying SLR approach reduced the accumulated snow/ice by as much as 3 inches in some places and more than 1 inch over a large region. Units: inches 30-h Accumulated Snow/Ice

Sample Rime Factor Modified SLR snowfall 24 hr snowfall forecast ending 00Z 27 November 2014: Washington D.C. ~4-6” New York City ~6-8” Philadelphia ~6-8” Boston ~3-6” 24 hr NAM snowfall forecast (Roebber SLR) BUT…. Rime Factor valid 17 UTCRime Factor valid 19 UTCPOFP valid 17 UTCPOFP valid 19 UTC High rime factor values in major cities indicate more heavily rimed particles (lower snowfall amounts) Relatively low percentage of frozen precipitation (50% or less)

Therefore, taking rime factor and POFP into account…. 24 hr NAM snowfall forecast (RF-modified Roebber SLR) 24 hr snowfall forecast ending 00Z 27 November 2014: Washington D.C. <1” New York City ~2-4” Philadelphia ~1-3” Boston ~3-6” WPC snowfall analysis

WPC-HMT Winter Weather Experiment 2015 (Morning) Sample Forecast and Visual Verification WPC 24-hr Snowfall Analysis VT 00Z Feb 5, 2015 WWE 24-hr Snowfall Forecast (contours) and Analysis 24-hr snowfall FCST NAM Roebber SLR modified with Rime Factor VT 00Z Feb 5 24-hr snowfall FCST NAM SWE * Baxter SLR modified with Rime Factor VT 00Z Feb 5 QPF * Fraction of Frozen Precip * Rime Modified Roebber SLR SWE * Baxter SLR SWE * Rime Modified Baxter SLR NAM Implicit Snowfall SWE = model forecast for snow water equivalent with fraction of frozen precipitation included in the model run history

Snowfall Threat Score by Forecast Technique Red = Bias Removed QPF*POFP*Rime Factor Modified Roebber SLR Orange = Bias Removed Snow Water Equivalent * Baxter SLR (Climatology) Yellow = Bias Removed SWE * RF Modified Baxter SLR Green = Bias Removed SWE * 10:1 SLR Light Blue = 24-hour Snow Depth Difference Magenta = Bias Removed QPF * POFP * 10:1 SLR ● Equitable Threat scores are higher for Rime modified Roebber forecast (red) than Baxter forecasts (orange, yellow and green) The fraction of frozen precipitation x 10:1 SLR had highest threat score the past 2 seasons