Product Information
and others interested in the details of WPC operations. |
WPC MissionThe Weather Prediction Center (WPC) provides forecast, guidance, and analysis products and services to support the daily public forecasting activities of the NWS and its customers, and provides tailored support to other government agencies in emergency and special situations. We are here to assist and be a resource for you. We are available 24 hours a day, 7 days a week to alert you to the potential for significant weather events dealing with heavy rainfall or snowfall, to discuss quantitative precipitation forecasts and model differences relating to general weather and precipitation forecasts, and to provide forecast guidance into the medium range period (days 3 to 7). Most of the forecasters at the WPC have extensive experience at quantitative precipitation, heavy snow and medium range forecasting. |
Quantitative Precipitation Forecasts (QPFs)Forecasters at the WPC [and its predecessor organizations, NMC's Meteorological Operations Division, Heavy Precipitation Branch (HPB) and the Quantitative Precipitation Branch (QPB)] have been issuing QPFs since 1960. All QPFs incorporate the latest surface and upper air analyses, radar data, satellite data, and model guidance from the NAM, NGM, GFS and RUC displayed on N-AWIPS workstations. WPC also works in conjunction with meteorologists in NESDIS's Synoptic Analysis Branch (SAB) to obtain information regarding satellite trends, precipitation and moisture availability estimates. This co-location and collaboration between SAB and WPC is bureaucratically known as the National Precipitation Prediction Unit (NPPU). A Senior Branch (lead) Forecaster (SBF) is on shift at all times. He or she is responsible for producing the day 1 24-hour precipitation forecasts, coordination of all WPC products (both internally and with other NWS offices), and center administrative operations after business hours. In addition to normal duties, the SBF participates in the East Coast winter storm and NHC hurricane conference calls regarding heavy precipitation, occasional unscheduled FEMA conference calls and numerous media interviews. |
24 Hour QPFs
Isohyets of expected basin average rainfall of 0.01, 0.25 inch, 0.50 inch, 1 inch, and 1.50 inch and greater (in inch increments) are drawn for three consecutive (Days 1-3) 24 hour forecast periods ending at 0000Z (for issuance times between 1815Z and 2215Z) and 1200Z (for issuance times between 0615Z and 1015Z). An electronically generated bulletin, which describes the location of the forecast isohyets using latitude and longitude points, is transmitted at the end of the QPF discussion for the Day 1 through Day 3 final products. Example:
The first field is the value of the contour (in
this case...0.25" or 0.50"). The following fields are the latitude/longitude pairs
for the contour. The first three digits of the pair are the degrees of
latitude (in tenths of degrees North latitude). The last three digits of
the pair are the degrees of longitude (in tenths of degrees West longitude).
If the fourth digit is less than 5, a leading
"1" is added to indicate longitudes greater than or equal to 100° W.
From the above message, the following table gives the decoded lat/long
pairs:
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These forecasts depict isohyets of accumulated precipitation of 0.01, 0.25, 0.50, 1 inch and greater (in 1 inch increments) expected in each six hour period. The SBF generates the six-hourly forecasts for Day 1, including the 00-06 hour update (91e). Another meteorologist prepares the Day 2 and Day 3 six hourly products during 2 shifts per day (~9am-5pm/9pm-5am EST), issuing QPFs for eight consecutive six-hourly periods ending on synoptic hours. |
48-Hour Day 4-5 and 5-Day Total QPFsThe Day 4-5 Quantitative Precipitation Forecast (QPF) products are prepared by our medium-range forecasters twice per day, once at 7:00 AM EDT/EST (11Z/12Z) and again around 1:00 PM EDT/EST (17Z/18Z).Both forecasts are valid from the beginning of Day 4 through the end of Day 5, with the later issuance offset by 12 hours. For example, a forecast prepared at 7:00 AM EDT/EST September 2, 2004 would be valid for the 48 hour period from 12Z September 5, 2004 through 12Z September 7, 2004. The forecast prepared at 1:00 PM EDT/EST September 2, 2004 would be valid from 00Z September 6, 2004 through 00Z September 8, 2004. The 5-Day Quantitative Precipitation Forecast (QPF) products are created by adding WPC's 6-hour QPFs for Days 1-3 (a total of 12 6-hour periods) to a 48-hour forecast for Days 4-5 prepared by our medium-range forecasters. This forecast is issued twice per day, once at 7:00 AM EDT/EST (11Z/12Z) and again at 7:00 PM EST/EDT (23Z/00Z). Both forecasts are valid from the beginning of Day 1 through the end of Day 5, with the later issuance offset by 12 hours. For example, a forecast prepared at 7:00 AM EDT/EST September 2, 2004 would be valid for the 120 hour period from 12Z September 2, 2004 through 12Z September 7, 2004. The forecast prepared at 7:00 PM EST/EDT September 2, 2004 would be valid from 00Z September 3, 2004 through 00Z September 8, 2004. |
Excessive Rainfall Potential
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QPF Forecast Verification:6-hourly precipitation forecasts are verified using a point (station) method while 24 hour forecasts are verified using an areal method. Current graphs depicting WPC verification scores are available on the WPC Verification page. For more details about the verification of WPC precipitation forecasts, read the article by Olson, Junker and Korty in Weather and Forecasting.Volume 10, 1995, pgs. 498-511. |
Medium Range/Extended (3-7 days)
The medium range graphical forecast products include:
All of these forecasts are generated twice per day. A preliminary, unofficial, set of graphics is issued by 1400 UTC and are intended for inter-office coordination purposes only. The surface pressure patterns and fronts on the preliminary forecasts are currently only drawn for the continental U.S. The final set of graphics is issued by 2:00 pm ET, with the surface pressure patterns and fronts encompassing much of the Northern Hemisphere. In addition to the graphical forecasts, the forecasters prepare two daily written discussions highlighting forecast reasoning and significant weather expected to impact the continental U.S. and Alaska during the day 3-7 time frame. One is available by 1400 UTC and accompanies the preliminary graphics, while the final narrative incorporates the latest model guidance and is issued at 2:30 pm ET. Forecasters also provide a separate discussion describing model differences and preferences across Hawaii. Two meteorologists work this shift once per day. One produces the 3-7 day pressure systems/fronts and written discussions for the continental U.S. and AK, while the other prepares the 48-hour and 5-day QPFs, 3-7 day temperature and probability of precipitation forecasts, and the Hawaiian discussion. They routinely use output from the GFS, ECMWF, and UKMET medium range models and also consider the Canadian, the Navy's NOGAPS model and ensembles. During hurricane season, at 1200 noon ET time on a daily basis since June 1, 1997, the medium range pressure forecaster participates in a conference call with the NHC via the Hurricane Hotline to discuss current and potential tropical activity in the Atlantic and Eastern Pacific oceans and how the medium range models are handling the situation. |
Model DiagnosticsThe WPC model diagnostic meteorologist prepares the Model Diagnostic Discussion which consists of three sections: 1) An evaluation of the analyses of the primary models (NAM, GFS) 2) A review of model trends and biases. 3) A description of model differences and preferences through 84 hours. This discussion is issued twice during each of the day and night shifts, and may include evaluation of short range ensemble forecasts (SREFs) and other global models.
The following table shows the deadline and content for each issuance.
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Issuance Time | Content |
0400Z/1600Z | Evaluate NAM initialization and trends from previous runs |
0530Z/1730Z | Evaluate GFS initialization Review GFS trends from previous runs Discuss model differences and preferences |
During the cool season (Nov 1 - Apr 15), this meteorologist is also primarily responsible for requesting reconnaissance flights whenever the potential exists for major winter storm development over the East or Gulf Coast states. During the Atlantic hurricane season (June 1 - Nov 30), he or she coordinates with the National Hurricane Center (NHC) whenever a tropical cyclone is located west of 60 degrees West longitude in the Atlantic basin, Caribbean Sea, or Gulf of Mexico. |
Surface Analysis ProductsThe following chart indicates the approximate issuance and web posting schedule for the WPC Surface Analysis. This product depicts the analysis of synoptic and sub-synoptic/mesoscale surface features including highs, lows, fronts, troughs, outflow boundaries, squall lines, and drylines. The analysis domain covers most of North America, the Western Atlantic and Eastern Pacific oceans, and the Gulf of Mexico.
PLEASE NOTE: The Pacific Ocean analyses (East and West Pacific) are prepared by NCEP's Ocean Prediction Center. |
Probabilistic Heavy Snow/Icing Forecasts
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