Weather Prediction Center (WPC) Winter Weather Desk Operations

2016-17 Weather Prediction Center (WPC) Winter Weather Desk Operations
Hi everyone, this is Dan Petersen, and I look forward to chatting with you today regarding winter weather forecast operations at the Weather Prediction Center and our forecast and decision support services to the forecast offices across the country. Dan Petersen, Bruce Veenhuis, Mike Bodner, Mark Klein, Chris Bailey

Winter Weather Forecast Desk Updates
Days 1-3 Probabilistic Snow/Ice Forecasts Revised freezing rain accumulation calculation Days 4-7 Winter Weather Forecasts Collaboration updates Forecast Verification What we’re going to cover today encompasses a review of current forecast operations, updates to the days 1-3 probabilistic snow and freezing rain forecasts, a revised calculation of the forecast freezing rain accumulations, Updates to the days 4-7 winter weather forecasts, collaboration updates (include WPC/WFO snow comparison graphics), and snow forecast verification.

Operations and Changes
Winter Weather Desk Operations and Changes Workflow: Winter Weather Desk remains operational 24 hours, 7 days a week Day Shift 12-21z Night shift 00-09z. Coverage and forecast updates between shifts 21z-00z and 09-12z event-driven Probability/percentile/deterministic forecasts of snowfall and freezing rain over the contiguous US in 12, 24, 48 and 72-hour increments Revised winter weather web page and graphics The winter weather desk is operational 24 hours a day. The scheduled shifts are 12-21z and 00-09z. Shift coverage is provided for collaboration-intensive events using comp time or overtime to fill gaps between shifts. So for example, if we see potential for a blizzard impacting multiple states that is likely to lead to media calls and multiple conference calls with Weather Forecast Offices, we will then call someone in to assist on the winter weather desk. We are still authorized to issue intermediate updates to forecasts in between shifts per collaboration with forecast offices. We will continue issuing the same probability, percentile, and deterministic forecasts over 12, 24, 48, and 72 hour intervals. Also, we have revised the winter weather page and graphics for this year, and I will show you the revised page.

Probabilistic Winter Precipitation 2015-16 Forecast Ensemble Composition (day shift)
63 members total (SREF 41 percent of all members) 26 SREF members 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 This is a list of the models/ensembles used in last year’s probability forecasts. Note the SREF had 41 percent of the members of the suite of probability forecasts, which will be decreased to 37 percent of the members for Also note the GEFS had 5 members in the forecast suite, and has been increased to 10 members for this year.

70 members total (63 members last season) New Members:
Probabilistic Winter Precipitation Forecast Ensemble Composition (day shift) 70 members total (63 members last season) New Members: 10 GFS ensemble members (06Z, up from ) 1 High res WRF ARW (00z) 1 High res WRF NMMB (00z) 2 prior cycle runs of GFS after ARW/NMMB Days 2-3 The total number of model and ensemble members in the winter probability forecasts has increased from 63 to 70. The number of GEFS members has increased from 5 to 10. We are now including the 0z run of the high res WRF ARW and NMMB on day 1. This high res window runs are replaced with prior cycle runs of 00 and 06z gfs on days 2 and 3, so 3 runs of the gfs are part of the suite of forecasts used to compile the probabilities. The 12z versions of the high res window runs are not available on day shift when the winter probabilities are compiled. ftp://ftp.wpc.ncep.noaa.gov/pwpf/conus_2.5km

2016-17 Forecast Ensemble Composition (day shift)
WRF ARW 00Z GFS 00Z WRF NMMB 00Z GFS 06Z NAM Nest 12Z NAM Nest 12z Parent NAM 12z GFS 12Z Canadian Model (CMC) 00Z ECMWF Operational 00Z ECMWF Ensemble Mean 00Z GEFS Ensemble Mean 06z 10 GEFS Ensemble Members 06z WPC Deterministic 26 SREF Ensemble Members 09Z 25 ECMWF Ensemble Members 00Z For the season, here is a table of the models and ensembles used in compiling the snow and freezing rain probability forecasts. We start on day 1 with the WRF ARW. In the next column is the day 2 forecast, where the ARW gets replaced by the 00z run of the GFS on day shift, and 12z run of the gfs on night shift. In the next row, we see the day 1 forecast includes the 00z WRF NMMB. In turn, the WRF NMMB gets replaced by the 06z GFS for days Likewise, the NAM Conus Nest gets replaced by the parent NAM on day 3. The other models/ensembles remain the same for all 3 days.

Web Site Display Changes for 2016-17 New Winter weather page http://www.wpc.ncep.noaa.gov/#page=wwx
Here is the new winter weather web page. At the top, we see a listing of hazards and highlights exist in difference colors for different risks for heavy snow. There is a link for the legacy page to show the color-filled probabilities, which remain on the same page as last year. At the bottom are links which also bring up last year’s page. I am going to give a demo here on how to navigate the page.

Web Site Display Changes for 2016-17 Transition to ESRI Maps
Here is the page showing the new mapping display, as we have switched using the google maps to using the ESRI maps and topographic backgrounds. The use interface has radio buttons for the ESRI map or you can toggle to display the corresponding GIF image.

2016-17 Freezing Rain Accumulation (FRAM) Calculation
Freezing rain accumulation rates decrease as precipitation rate increases(top), increase with wind speed (middle), and decrease as wet bulb temperatures increase (bottom) Sanders and Barjenbruch, 2016 Sanders and Barjenbruch (2016) have a published paper in Weather and Forecasting summarizing their research on freezing rain accumulations on both flat and radial surfaces. For simplicity we will be looking at flat surfaces. The journal article shows freezing rain accumulation rates decrease as precipitation rates increase (top), increase with wind speed (middle) and decrease as wet bulb temperatures increase to near freezing.

2016-17 Freezing Rain Accumulation (FRAM) Calculation
e. The median Ice to Liquid Ratio for elevated horizontal ice accumulation was 0.72:1 with a 25th percentile of 0.50:1 and a 75th percentile of 1.0:1 e. AT WPC we will adopt the equation covering the ice to liquid ratios as a function of precipitation rate. The horizontal green line corresponds to a ice to liquid ratio of one. It looks as though ice to liquid ratios are greater than one to one when precip rates are less than 0.03 inches per hour. Ice to liquid ratios are less than 1:1 when precip rates are greater than 0.03 inches per hour. Last year we used one to one ice to liquid ratios. This formula will result in high ratios and resultant greater ice accumulations only when precip rates are less than 0.03 inches per hour. At higher precip rates, accumulations will be lighter than last year’s output would have provided. WPC will adopt the equation covering the precip rate, which accounts for 80 percent of the weight of the factors. Ice to Liquid Ratio = x (P)exp where P=Precipitation Rate

Days 4-7 Probability Forecasts
Probability of exceeding 0.25” of combined snow/sleet Forecasts for will be provided from 12z to the following 12z (24 h intervals) for Days 4, 5, 6, and 7 both on day and night shift The days 4-7 winter weather outlook site is shown here, with a tab for each 24 hour forecast. The Forecasts will cover the 12z to the following 12z period each 24 hour period for days 4, 5, 6, and 7. At the top is a feedback link where people can provide their comments for improvement. The first link at the bottom shows the site where the graphics are displayed, which can now be viewed external to the weather service. The second link shows the availability of the forecasts an experiment in the suite of ndfd forecasts, and the availability of the grids for ingest and display in awips.

Forecasts for Day 4, Day 5, Day 6, and Day 7 The days 4 to 7 probability forecast are a joint probability of the probability of QPF exceeding a quarter inch for each 24 hour period multiplied by the probability the precipitation type will be snow or ice pellets to determine the probability the accumulation of snow/ice pellets exceeds a quarter inch. Ensemble Probability of Snow/Ice Pellets Probability of Snow/Ice Pellets > 0.25” Probability of WPC QPF >= .25 “ × =

Methodology Future Work Probability of Frozen Precipitation We sue the GEFS ensembles and Canadian ensemble forecasts to determine the precipitation type probability. Since the WPC QPF is issued in 48 hour blocks for days 4-5 and 6-7, it needs to be disaggregated into 24 hour blocks to determine the amounts for each day. This is done using the ensemble mean QPF from both the GEFS ensemble mean QPF and also the Canadian ensemble mean QPF. Determination of precipitation type via GEFS, CMCE members Average of GEFS + CMCE ensemble mean QPFs used to disaggregate Days 4-5 and Day 6-7 WPC QPF Thermal Probability Fields for all 3 Guidance sets

Day 4-7 Winter Weather Product We edit draft probabilities, including those from the ECMWF ensembles (upper right) Here is an example of the underlays using in composing the probability of combined snow/sleet forecasts. In the upper left is the probability using the Canadian ensembles only. In the upper right is the probability using the ECMWF ensembles only. In the lower left is the probability using the GEFS ensembles only. The WPC forecast in the lower right can be edited and adapted to any of the 3 forecasts or a combination of forecasts. 24-hour probability of at least 0.10” of winter precipitation(ending 2/17/2015, 12Z)

Winter Weather Watch Collaborator
Summary option Probability option The winter weather watch collaborator is undergoing a slight redesign for this year. On the left are radio buttons to display the 30 or 50 percent summary maps of the probability of exceeding WFO watch/warning criteria. On the right are radio button to review the probability of snow or freezing rain exceeding WFO watch/warning criteria, provided in 6 hour time steps. The forecasts themselves are shown in 24 hour time intervals. Forecasts of probability of exceeding WFO watch/warning criteria, with summary maps where probabilities exceeded 30 or 50 percent. Displays show summary graphics and probabilities for each time step

In the watch collaborator, when the probabilities are chosen, a menu appears to allow to allow for control of stepping or looping through the individual forecasts. Once you change to a new forecast, the valid time both in the legend at above the top of the map should change in concert. When you select the probability forecasts, The forecasts are available in 6 hour time steps controlled by the forward and backward buttons, play, rock, etc.

Graphics have both a 30 percent contour and 50 percent probability of exceeding 12/24 hour winter storm watch criteria Like last year, there will be an option to have the display show where there is either a 50 percent probability or greater of exceeding local watch/warning criteria for both snow and freezing rain, or a 30 percent probability. The color scale changes depending on which value you choose. On the right is the existing graphic we have showing 24 hour snow watch/warning criteria across the country. Let us know if you are making any changes to the 12 or 24 hour watch/warning criteria values and where we need to adjust the map. 24 hour winter storm watch criteria for snow(in)

New WFO/WPC Forecast Snow Comparison Graphic
WPC-NDFD snow difference graphic issued once the draft WPC snow amounts are sent for internal collaboration with WFOs NDFD Also new for this year will be a comparison graphic. Many of you have seen on one of our QPF collaboration pages we have a comparison of WPC QPF vs. the WFO QPF. Here we will show a comparison of WPC snow accumulations vs. the NDFD accumulations to help identify areas where collaboration is needed to resolve differences. In the top left will be the WPC forecast snow amount, the top right will show the NDFD snow amount forecasts, and the bottom will show the difference graphic. This will be included in the internal winter weather site. WPC-NDFD

2015-16 WPC Winter Weather Forecast Verification

2015-16 Low Tracks Verification
Here is the verification of the surface low tracks from each model, ensemble mean and combination of the gfs and nam plus the gfs plus ecmwf. The vertical scale is the distance error in nautical miles of the forecast surface low position, and along the bottom is each forecast hour from 12 to 72 hours. Among the operational models, the ecmwf was best at 60 and 72 hours, but the gfs was a few miles better at 36 and 48 hours. At 48, 60, and 72 hours the gefs mean had lower position errors than the operational gfs. ECMWF lowest distance error for low positions amongst models hours, GFS+ ECMWF blend for combination of models

Improving Collaboration and Verification: Common Analyses
NOHRSC Snowfall Analysis (V1) -poor quality in data sparse areas and terrain Season January 27-28, 2015 Snowstorm 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 (starting in Jan?) Operational NOHRSC Development The NOHRSC analysis appears to work well in population centers with many snowfall reports. The image at the top shows the current operational analysis for the snow totals for the past season. Note the gaps in the west, northern ND/MT and northern ME. In the lower left panel, the current analysis is shown for a single event. Greg Fall came to our workshop with the MSDs and SSDs and demonstrated proposed improvements to the analysis, and showed what the revised analysis would look like in the lower right, which better captures snowfall variations commonly seen in sharp gradients in terrain. It also got rid of an anomalously large maxima of snow in southern CA. NOHRSC petitioned HQ for contractor support to improve the analysis and my understanding was funding was given to fund this project back in September.

WPC Deterministic Snow Verification
Day One Snow Threat Score Over the CONUS (Coop data) Better Here is the day 1 deterministic snowfall verification for the season using the verification with respect to the cooperative observer data, showing threat scores for the 4, 8 and 12 inch thresholds of 24 hour snow accumulation. The edits by the operational winter weather forecasters did not provide for an improvement over the automated ensemble for 4 and 8 inches, but did for 12 inches. The next slide will cover the season. Final forecasts did not improve upon the Automated Ensemble for 4, 8, but did for 12” Automated Ensemble: NAM + GFS + ECMWF + SREF members + GEFS members + ECMWF members

Day One Snow Threat Score Over the CONUS (Coop data) Better Here is the day 1 deterministic snowfall verification for the season, showing threat scores for the 4, 8 and 12 inch thresholds of 24 hour snow accumulation. The threat scores increased from last year to this year. For all 3 criteria, the edits provided by the human forecaster made improvements in the forecaster over the automated ensemble. The next slide will cover the bias score for the season. Final forecasts improved upon the Automated Ensemble for 4, 8, and 12” Automated Ensemble: NAM + GFS + ECMWF + SREF members + GEFS members + ECMWF members

High bias above this line
WPC Deterministic Snow Verification Day One Snow Frequency Bias Over the CONUS (Coop Data) High bias above this line This is for the day one forecast across the 4,8, and 12 inch thresholds. The white horizontal line is unbiased, with values above this line considered to be a high bias and values below this line considered to have a low bias. Here the frequency bias values are much closer to the desired value of 1 for all 3 thresholds. Here the human edits slightly increase the bias for all thresholds. Notice the low bias for 12 inches, with the human edits making the bias closer to one, which was an improvement. Bias performance show major improvement for both automated and human forecasts, and even have a low bias for 12”

Summary Winter Weather Desk (WWD) operational 24 hours/day , with day shift 12-21z and night shift 00-09z New WPC NDFD comparison snow accumulation forecast graphic to aid collaboration process WPC has adopted the Sanders and Barjenbruch model for freezing rain accumulations (FRAM) Days 1-3 Probabilistic Snow/Ice Forecasts now at 70 members to reduce SREF weighting Experimental Days 4-7 Forecasts are issued to public and available in NDFD Verification using Coop Observer reports shows slight high bias for 4, 8 inches but slightly low bias for 12 inches

Questions or Comments? Dan Petersen WPC Forecast Operations Branch (301) (Winter Weather) (301) (QPF, Lead Forecaster)

Winter Weather Desk Resources
Winter Weather Desk Methodology: WPCQPFtoWinterweatherdeskmethodology.pdf Probabilistic Winter Forecasts: ftp://ftp.wpc.ncep.noaa.gov/pwpf/conus_2.5km/ Probability Forecasts available on Satellite Broadcast Network: Snow to liquid ratio calculations: LR_reference.pdf Virtual Lab presentation on precipitation type (Chenard, Schumacher):

WFO/WPC Collaboration by Year
This is a display of the 6 year trend of collaboration between WFOs and WPC with a different color bar for each year. We had a total of 46 multi-office collaboration calls, which set a new record. In the chart, on the left is the number of chat questions using 12planet, which will be swapped for the awips collaborator chat for this season. The higher totals in are due to the greater number of events in the northeast. The number of comments shows an overall upward trend as well, but not as high as the spike in activity. Finally the number of individual office calls has a long term upward trend. 46 Multi-office collaboration calls, a new record volume

Collaboration Guidelines Snow and freezing rain forecasts:
WFO-WFO collaboration guidelines listed at Use these for WPC-WFO Collaboration 24 hour Snow accumulation: >2” WPC/WFO difference snow <6” >4” WPC/WFO difference snow <8” >8” WPC/WFO difference snow >12” 24 hour Ice Accumulation: >0.1” difference for WPC/WFO ice <0.5” >0.2” difference for WPC/WFO ice <1.0” >0.4” difference for WPC/WFO ice >=1.0 This year’s revised collaboration guidelines were based on published WFO-WFO collaboration guidelines on the posted web page. We thought it would be good to apply this to the WPC-WFO collaboration values. We should chat or have a conference call to discuss, for example, a difference of greater than 2 inches of snow if total snow amounts are forecast to be less than 6 inches in a 24 hour period. Likewise we would collaborate to resolve ice accumulation forecast differences greater than a tenth of an inch for an events in which less than half an inch is forecast. Notice we’re not looking to create an exact match, but have similar messaging regarding an event’s potential and expected impacts.

Conference Call Collaboration Guidelines
Have a call if Winter Watch Collaborator shows >30% chance of snow/freezing rain exceeding local watch/warning criteria over 2 or more County Warning Areas Calls facilitated by Regional Operations Center (ROC) on day shift and WPC at night/weekends/holidays when no ROC support Calls held 0615/1815Z, with WPC issuing a NIMNAT message in AWIPS to provide call-in #/time WPC focuses on model differences/preferences, forecast confidence WFO focus on items impacting their watch/warning/advisory decisions and forecast items impacting decision support

Central Region (CR) QPF/Winter Weather Test
0530z/1730Z CR offices run a multi-model superblend (minus the ECMWF) to determine draft snow/ice accumulations, and then collaborate (WPC can use ECMWF in blend) Last year’s CR test had 40% continuity, this year’s will have 0% Please share your draft snowfall accumulations, precipitation type and snow ratios, and ice ratios with WPC in AWIPS Intersite Coordination Grids! CR WFOs have about 2.5 hours for collaboration, which overlaps with WPC collaboration

Day One Snow Threat Score Over the CONUS (NOHRSC analysis Better Here is the day 1 deterministic snowfall verification for the seaon, showing threat scores for the 4, 8 and 12 inch thresholds of 24 hour snow accumulation. The analysis used in the verification is the NOHRSC site shown at the top. The automated ensemble is a multi-model/ensemble average whose members are shown at the bottom of the screen. The final forecasts are the human forecasts, which consists of the edits made by the operational winter weather forecasters in conjunction with input from field forecasters. For all 3 criteria, the edits provided by the human forecaster did not make any improvements over the automated ensemble. The next slide will cover the bias score. Final forecasts did not improve upon the Automated Ensemble for 4, 8, and 12” Automated Ensemble: NAM + GFS + ECMWF + SREF members + GEFS members + ECMWF members

Day One Snow Threat Score Over the CONUS (NOHRSC analysis Better Here is the day 1 deterministic snowfall verification for , showing threat scores for the 4, 8 and 12 inch thresholds of 24 hour snow accumulation. The analysis used in the verification is the NOHRSC site shown at the top. The automated ensemble is a multi-model/ensemble average whose members are shown at the bottom of the screen. The final forecasts are the human forecasts, which consists of the edits made by the operational winter weather forecasters in conjunction with input from field forecasters. For all 3 criteria, the edits provided by the human forecaster did not make improvements over the automated ensemble. The next slide will cover the bias score. Final forecasts did not improve upon the Automated Ensemble for 4, 8, and 12” Automated Ensemble: NAM + GFS + ECMWF + SREF members + GEFS members + ECMWF members

WPC Deterministic Snow Verification Day One Snow Frequency Bias Over the CONUS (NOHRSC analysis ) Better High bias above this line And the complement to the threat score is the bias. This is for the day one forecast across the 4,8, and 12 inch thresholds with respect to the NOHSRC analysis. The white horizontal line is unbiased, with values above this line considered to be a high bias and values below this line considered to have a low bias. Here the human edits do not improve the automated bias much, and all three criteria have a high bias. Part of the bias is possibly due to high qpf, and part due to gaps in observation coverage, especially in remote areas. Both automated consensus and human final forecasts have a high bias, especially for 12”

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

Day Two Snow Threat Score Over the CONUS (Coop Observer Analysis) Better Final forecasts outperform the Automated Ensemble for 8 and 12 inches, but barely for 4 inches

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

WPC Deterministic Snowfall Forecast Day Two Snow Frequency Bias Over the CONUS (Coop Observer) High bias above this line Automated and Final forecasts have a much lower bias, especially for 12”

Day Three Snow Threat Score Over the CONUS (NOHRSC) Better Automated Ensemble forecasts outperform the final for 8 and 12” forecasts

Day Three Snow Threat Score Over the CONUS (Coop Observer) Better Final forecasts outperform the Automated Ensemble for 4, 8, and 12” forecasts

WPC Deterministic Snowfall Forecast Day Three Snow Frequency Bias Over the CONUS (NOHRSC) High bias above this line 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)

WPC Deterministic Snowfall Forecast Day Three Snow Frequency Bias Over the CONUS (Coop Observer) High bias above this line High bias now reversed to low bias, especially for 12” NOHRSC high bias may be associated with snow analysis problems (no data=no accumulating snow)

Day 1 PWPF Verifying frequency over CONUS (Coop Data)
WPC Probabilistic Snowfall Verification Day 1 PWPF Verifying frequency over CONUS (Coop Data) Low bias Verifying frequency Forecast frequency Events forecast more frequently than observed

Day 1 PWPF Verifying frequency over CONUS (NOHRSC Data)
WPC Probabilistic Snowfall Day 1 PWPF Verifying frequency over CONUS (NOHRSC Data) Low bias Verifying frequency Forecast frequency Events forecast more frequently than observed

SREF Forecast Plume of Snow Amounts for Washington DC (DCA) from 21z 20 Jan verifying 12z 24 Jan 2016 Forecast amounts range from 0 to 40 inches, with a mean of 15 inches DCA event record 28: Over dispersive! Observed 18.8” Here is a forecast plume diagram of the SREF forecast snowfall totals for Washington DC 2 days prior to the January blizzard. The totals ranged from zero to a little over 40 inches. The record snow is 28 inches so the high end is a foot over the record event total. The goal posts were quite wide, and unrealistic in my opinion, as the other models and ensembles did not have any zero accumulation or a peak near 40 inches. I think the SREF system forecasts can be over dispersive. DCA observed 18.8” for this event.

SREF Forecast 24 Hour Precip (left) vs
SREF Forecast 24 Hour Precip (left) vs. Observed (right) verifying 12z 23 Jan 2016 A common occurrence last winter was for cluster of the WRF ARW members having a different track from the NMMB members, often further northwest in the ARW members. This resulted in the mean QPF being shifted further northwest than most other model/ensemble forecasts. The SREF forecast here in the Ohio Valley was 5-10 mm while the observed amounts on the right showed zero to 5 mm, so the observed amounts were lower than the forecast. SREF Precip extended too far northwest into southern IL/IN/OH

WPC snow to liquid ratio (SLR) calculation
Snow to Liquid Ratio Method: NAM Rime Factor modified Roebber Snow Ratio + NAM Rime Factor modified Baxter Climatology Snow ratio + GFS Roebber Snow Ratio+ Baxter Climatology Snow ratio + 11:1 The snow to liquid ratio

Weather Prediction Center (WPC) Winter Weather Desk Operations

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