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Product Information



QPF Overview Medium/Extended Range
Excessive Rain Alaskan Desk
QPF Verification Model Diagnostics/Biases
Mesoscale Precip Discussion Surface Analysis
Short Range International Desks
Storm Summaries Winter Weather
  Tropical Public Advisories


The following provides technical information on the WPC for forecasters 
and others interested in the details of WPC operations.

WPC Mission

The 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)

QPF example

Forecasters at the WPC and its predecessor organizations have been making Quantitative Precipitation Forecasts since 1960. Quantitative Precipitation Forecasts, or QPFs, depict the amount of liquid precipitation expected to fall in a defined period of time. In the case of snow or ice, QPF represents the amount of liquid that will be measured when the precipitation is melted. Precipitation amounts can vary significantly over short distances, especially when thunderstorms occur, and for this reason QPFs issued by the WPC are defined as the expected "areal average" (on a 20 x 20 km grid) in inches.

Methods for producing QPFs are similar to other meteorological forecasts. First, meteorologists analyze the current state of the atmosphere. Then they use model forecasts of pressure systems, fronts, jet stream intensity, etc., to form a conceptual model of how the weather will evolve. The WPC has unique access to the full suite of operational and ensemble model guidance from modeling centers in the U.S., Canada, and Europe (the foreign models are global models, so they also make predictions over the U.S.). The WPC also stores output from several consecutive runs of all of these models, allowing for trend analysis of model QPFs. Forecasters determine which models are showing a reasonable amount of precipitation in roughly the correct place and time. Those choices serve as the starting point for QPFs, but forecasters also make manual adjustments based on their experience.

WPC forecasters often engage in discussion with some of the 122 local National Weather Service Forecast Offices, 12 River Forecast Centers, and other national centers such as the Storm Prediction Center and National Hurricane Center. In fact, per a 2005 agreement, the WPC provides the rainfall forecast (known as a rainfall statement) that the National Hurricane Center inserts into each tropical cyclone advisory it issues. The WPC is also co-located with NOAA's National Environmental Satellite, Data, and Information Services (NESDIS) Synoptic Analysis Branch (SAB). The SAB provides information on satellite trends which helps refine short range QPFs. Together, the SAB and Day 1 QPF desk at the WPC are known as the National Precipitation Prediction Unit (NPPU). This collaborative process makes WPC forecasts generally more accurae than any individual model, and consecutive versions of WPC forecasts do not differ as much as consecutive model forecasts sometimes do.

Technical Description of QPFs:

The QPF contours (isohyets) are drawn to encompass areal average amounts of 0.01, 0.25 inch, 0.50 inch, 1 inch, 1.50 inches, and 2.00 inches. Any values greater than 2.00 inches are drawn in one-inch increments. In addition, the location of QPF maxima are indicated on the chart by an "X", with the associated maximum value printed underneath. It is important to note the valid time period when viewing each product. Specifically, for the Day 1, 2, and 3 forecasts, QPFs are manually created for 6-hour periods and an accumulated 24-hour total QPF is also issued. For the Days 4/5 and Day 6/7 QPF, forecasters manually create a 48-hour accumulation of areal average rainfall. Computer programs then take advantage of model forecasts of the timing of precipitation to break the WPC forecast down into 6-hourly QPFs. Forecasts issued on the day shift correspond to periods ending at 0000Z (for issuance times between 1815Z and 2215Z), and those issued on the night shift correspond to periods ending at 1200Z (for issuance times between 0615Z and 1015Z).

Multi-day Accumulation Products:

Through simple addition of the various 24-hour and 48-hour QPFs, WPC is able to provide multi-day accumulation forecasts. Days 1-3, Days 1-5, and Days 1-7 accumulations are made available, and can be powerful planning tools for many applications.

Schedule of QPF Issuance:

Valid Period Issuance Time
Preliminary      Final
Valid Period Length of
Valid Period
Night Shift*        
Day 1 0600Z   06Z Today (Day 1) - 12Z Tomorrow (Day 2) 30 hours
Day 1   1000Z 12Z Today (Day 1) - 12Z Tomorrow (Day 2) 24 hours
Day 2 0600Z 1000Z 12Z Tomorrow (Day 2) - 12Z Day 3 24 hours
Day 3 N/A 0800Z 12Z Day 3 - 12Z Day 4 24 hours
Days 4 and 5 N/A 0830Z 12Z Day 4 - 12Z Day 6 48 hours
Days 6 and 7 N/A 0830Z 12Z Day 6 - 12Z Day 8 48 hours
Day Shift        
Day 1 1800Z   18Z Today (Day 1) - 00Z Tomorrow Evening (Day 2) 30 hours
Day 1   2200Z 00Z This Evening (Day 1) - 00Z Tomorrow Evening (Day 2) 24 hours
Day 2 1800Z 2200Z 00Z Tomorrow Evening (Day 2) - 00Z the Evening of Day 3 24 hours
Day 3 N/A 2000Z 00Z Day 3 - 00Z Day 4 24 hours
Days 4 and 5 N/A 2030Z 00Z Day 4 - 00Z Day 6 48 hours
Days 6 and 7 N/A 2030Z 00Z Day 6 - 00Z Day 8 48 hours

* Forecasts made on the night shifts are verified versus observed rainfall. The valid time of 1200z to 1200z for QPFs issued by the night shift coincides with the 24-hour observation cycle for National Weather Service Cooperative Observers and many other rainfall networks such as CoCoRaHS.

All Times shown are in Zulu (Z), or Greenwich Mean Time, and correspond to the time in Greenwich, England, as seen on a 24-hour clock.


Excessive Rainfall Outlooks

Excessive Rainfall Example

The Excessive Rainfall Outlooks provide a forecast of the risk of flash flooding across the continental United States. As of October 5, 2004, the graphics display the probability that precipitation will exceed the flash flood guidance values issued by the River Forecast Centers (RFCs). A closed contour with an arrowhead delineates the probability forecasts, with risk areas defined to the right of the direction of the arrowhead.

On June 29, 2006, the probability categories were changed due to calibration studies conducted at WPC. The calibration for the excessive rainfall graphics are based on the frequency of events for which observed rainfall exceeded flash flood guidance values for a given risk category. It is important to note that the probabilities assigned to each risk category are small numbers because the risk of flash flooding at any single location is relatively low, even when heavy rain is expected to fall somewhere in the vicinity. When forecasters outline risk areas, however, they are expecting greater organization of excessive rainfall than would be observed under average conditions. As confidence of excessive rainfall increases the category respectively evolves from Slight to Moderate to High.

Risk Category Probability of Rainfall
Exceeding Flash Flood
Guidance at a Point
Slight (SLGT) 5-10%
Moderate (MDT) 10-15%
High (HIGH) >15%

If the potential exists for precipitation exceeding guidance values, but the expected probability for a point location is less than 5%, WPC will place the words SEE TEXT over the threat area. This area will then be referenced in the Excessive Rainfall Discussion.

In addition, areas where maximum precipitation amounts may exceed five inches will also be indicated by a red contour and hatching.

If conditions are not expected to become favorable for flash flooding then "Rainfall Not Expected To Exceed Flash Flood Guidance" is appended to the center of the graphic.

On June 5, 2007, WPC began producing Day 2 and Day 3 excessive rainfall forecasts. These forecasts were declared operational on February 11, 2008. Aside from the valid periods, there are several differences between these products and the Day 1 forecasts:

  • Only two probability categories are defined - SLGT and MDT.
  • Written discussion is provided in the routine Day 2/3 portion of the QPF discussion (QPFERD) rather than in a separate product. Furthermore, a text-based representation of the threat region is created and can be accessed at the link below the graphic.
  • Forecasts are issued only twice per day. See the table below for information regarding issuance and valid times.

Day 2 and Day 3 excessive rainfall forecasts are based on Flash Flood guidance for Day 1 and quantitative precipitation forecasts for Days 2 and 3, respectively. There is no Flash Flood guidance issued for Days 2 and 3. Forecasters must make an educated guess as to how the guidance will change (increase or decrease) in response to future precipitation amounts, for instance in the Day 1 period. Increased variability in model guidance and the inability of the models to resolve mesoscale features results in greater uncertainty in forecasting excessive rainfall for the day 2 and 3 periods. WPC forecasters examine various deterministic and ensemble models looking for synoptic patterns that favor organized areas of heavy rainfall and compare this to the Day 1 Flash Flood Guidance before depicting a threat area.

Note: Flash Flood Guidance values incorporate soil type, land coverage, and a host of other factors in an attempt to describe the rain rate necessary to yield significant surface runoff and flash flooding over a given area. The River Forecast Centers issue guidance values for 1-, 3-, and 6-hour periods. Flash Flooding is considered to be caused by rainfall occurring in 6 or fewer hours, whereas longer duration rainfall represents areal flooding or inundation. The WPC excessive rainfall products focus specifically on flash flooding.

Schedule of Excessive Rainfall Outlook Issuance:

Day-1 Excessive Rainfall Outlooks (graphic and associated discussion) are issued four times per day: 03, 06, 15, and 18 UTC. Day-2 and Day-3 versions are issued twice daily. The valid times varies as noted in the table below. For Day-1 the 03 Z and 15 Z issuances are valid for 21-hour periods, while the 06 Z and 18 Z issuances are valid for 30 hours. Unscheduled, event-driven updates may be issued as needed.

Valid Period Issuance Time Valid Period
Day 1 0300Z 03Z - 24Z (21 hours)
Day 1 0600Z 06Z - 12Z (30 hours)
Day 1 1500Z 15Z - 12Z (21 hours)
Day 1 1800Z 18Z - 00Z (30 hours)
     
Day 2 0630Z 12Z Day 2 - 12Z Day 3
Day 2 1830Z 00Z Day 2 - 00Z Day 3
     
Day 3 0830Z 12Z Day 3 - 12Z Day 4
Day 3 2030Z 00Z Day 3 - 00Z Day 4

 
Forecast Discussions/Text Products:

National Weather Service forecast discussions have been used for decades to summarize our assessment of the upcoming weather pattern and associated impacts. Discussions are also used to convey the forecasters' confidence in both the available model output and the manual forecast.

Schedule of QPF Discussion (QPFPFD) Issuance:

Valid Period Issuance Time
Preliminary      Final
Night Shift    
Days 1-3 0900Z 1100Z
Days 4-7* N/A 0700Z
Day 1 Excessive Rainfall Discussion   0230Z, 0700Z, and unscheduled updates
Day Shift    
Days 1-3 2100Z 2300Z
Days 4-7* N/A 1600Z
Day 1 Excessive Rainfall Discussion   1500Z, 1900Z, and unscheduled updates

* Days 4/5 and 6/7 QPFs are produced by the WPC medium range desk which issues a medium range forecast discussion (PMDEPD).

Text-based coding of the 24-hour QPF contours

Included at the end of the QPF Discussion for Days 1-3 is a bulletin that describes the shape of the forecast isohyets using latitude and longitude pairs. The order in which the pairs appear is important as this gives the contour or isohyet a clockwise direction as the points are plottd to create the contour. The forecast value associated with a given isohyet is valid in the enclosed area to the right of the direction in which the contour is drawn. The 0.50" contour described in the example below would represent an areal average of 0.50" forecast over parts of northwestern Colorado and southern Wyoming.

Example:
0.25 350731 349761 349789 347803 340819 327837 310854 297864 284874
0.50 404072 395071 390076 387081 389084 395085 402082 404076 404072

The first field is the value of the contour; in this case the values are 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 indiate longitudes greater than or equal to 100oW. From the above message, the following table gives the decoded lat/lon pairs:

Value: 0.25" Value: 0.50"
35.0N, 73.1W 40.4N, 107.2W
34.9N, 76.1W 39.5N, 107.1W
34.9N, 78.9W 39.0N, 107.6W
34.7N, 80.3W 38.7N, 108.1W
34.0N, 81.9W 38.9N, 108.4W
32.7N, 83.7W 39.5N, 108.5W
31.0N, 85.4W 40.2N, 108.2W
29.7N, 86.4W 40.4N, 107.6W
28.4N, 87.4W 40.4N, 107.2W

Tropical Rainfall Statement

Per an agreement between the WPC and the NHC dated March 13, 2005, the WPC is responsible for providing NHC with the wording for rainfall statements in all public advisories for tropical cyclones. The WPC provides rainfall statements for active tropical systems that threaten land masses in the Atlantic and eastern Pacific basins. The Tropical Rainfall Statement describes specific islands or continental regions expected to be impacted by heavy rain. The statements include a range of expected areal average rainfall as well as the maximum amounts expected at isolated locations.

QPF 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 on the verification of WPC precipitation forecasts, read the article by Olson, Junker and Korty in Weather and Forecasting. Volume 10, 1995, pgs. 498-511.


 
Mesoscale Precipitation Discussions

On April 9, 2013, WPC began providing short term guidance during heavy rain events leading to a threat of flash flooding to the National Weather Service (NWS) Weather Forecast Offices (WFOs), River Forecast Centers (RFCs), the media, emergency managers and interested partners. Guidance is given in the form of Mesoscale Precipitation Discussions (MPDs), that are ideally issued 1-6 hours ahead of time, averaging an area equal to roughly half the size of the state of Kansas. Each MPD consists of a graphic indicating the area of concern and any pertinent meteorological features as well as a brief text discussion focused on the mesoscale features supporting the anticipated heavy rainfall. The potential for flash flooding within the area of concern will be highlighted by one of three headlines:

FLASH FLOODING LIKELY High confidence exists that environmental conditions are favorable, or will become favorable, for heavy rainfall that will result in flash flooding.

FLASH FLOODING POSSIBLE Environmental conditions are favorable, or will become favorable, for heavy rainfall, but there are questions about how the event will evolve and/or whether flash flooding will occur.

FLASH FLOODING UNLIKELY High confidence exists that environmental conditions are unfavorable, or will become unfavorable, for heavy rainfall that will result in flash flooding. (typically issued toward the end of an event)

While flash flooding is caused by a variety of factors (e.g., intense rainfall, dam failure, ice jams), WPC's Metwatch desk will only focus on flash floods triggered by intense rainfall that occur over a sufficient areal coverage. Localized flash flooding is not considered.

The MPD appears under WMO Header: AWUS01 KWNH
and AWIPS header: KWNH FFGMPD


Medium Range/Extended (3-7 days)

Product Time
Day 3-7 500mb Height Forecasts 0200 UTC and 1400 UTC
Day 3-7 Fronts/Pressure Graphics for North America 0330 UTC and 1500 UTC
Day 3-7 Fronts/Pressure Graphics for the Northern Hemisphere 1900 UTC
Day 3-7 Min/Max/PoPs 0515 UTC and 1430 UTC
CONUS Grids 0600 UTC and 1530 UTC
Forecast Discussion 0700 UTC and 1600 UTC
Day 4-5 and Day 6-7 48-hour QPFs 0830 UTC and 2030 UTC
 
The medium range graphical forecast products include:
  • Surface pressure patterns, circulation centers, fronts, and 500mb heights for days 3-7 into the future
  • Daily maximum and minimum temperatures and anomalies for days 3-7
  • Daily precipitation probabilities for days 3-7
  • Two 48-hour QPFs encompassing Days 4-5 and Days 6-7
  • 5-Day Total QPF for Days 1-5 and a 7-Day Total QPF for Days 1-7
The surface pressure and fronts graphics are generated three times per day; the 0330 UTC and 1500 UTC issuances display features over the continental U.S. (CONUS) only, while the 1900 UTC issuance includes fronts and surface pressure fields for much of the Northern Hemisphere. The 500mb forecasts and Min/Max/PoP graphics are primarily focused on the CONUS and issued twice per day.

In addition to the graphical forecasts, the forecasters prepare two daily written discussions. They highlight medium-range model differences, provide weather solution preferences, a measure of uncertainty, forecaster reasoning and highlight any significant weather expected to impact the CONUS during the Day 4-7 time frame. Forecasters also provide a separate discussion describing guidance differences and preferences across Hawaii by 1230 UTC.

One meteorologist works during the overnight hours (0000-0900 UTC), while two prepare the forecasts during the day shift (1130-2030 UTC). The overnight forecaster generates a set of North American 3-7 day pressure systems/fronts and 500mb forecasts, 3-7 day sensible weather grids, two 48-hour QPFs, and discussion. During the day shift, the two meteorologists collaborate to generate a new set of these same medium range products along with Northern Hemisphere 3-7 day pressure systems/fronts, targeted observation guidance, 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 NAVGEM model, and ensemble guidance from the GFS, ECMWF, Canadian, and North American Ensemble Forecast System (NAEFS).

In addition, during hurricane season, at 1700 UTC on a daily basis since June 1, 1997, the medium range pressure dayshift forecaster also 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.


Alaska Medium Range (Days 4-8)

Product Time
Day 4-8 Fronts and Pressure Graphics 1800 UTC
Day 4-8 500 hPa Height Graphics 1800 UTC
Alaska Medium Range Discussion 1900 UTC
Day 4-8 Max/Min Temps and Probability of Precipitation Grids 2200 UTC

To accommodate a request for support from the NOAA National Weather Service (NWS) Alaska Region, the NCEP/Weather Prediction Center's (WPC) Alaska Medium Range Desk is issuing the following products:
  • Day 4-8 Surface Fronts and Pressures graphics
  • Day 4-8 500 hPa Height graphics
  • Alaska Medium Range Forecast Discussion
  • Day 4-8 Maximum/Minimum Temperature grids
  • Day 4-8 12-hour Probability of Precipitation grids
  • Day 4-8 derived Dewpoint Temperature, Cloud Cover, Precipitation Type, and Wind Speed/Direction grids
Surface graphics depict surface pressure patterns (from which surface winds can be inferred), high and low pressure circulation centers and fronts for days 4-8.  The 500 hPa height graphics display the general flow pattern forecast for days 4-8, and the gridded guidance depicts various important meteorological variables for the forecast period.

An WPC meteorologist interprets available deterministic and ensemble model guidance and collaborates with the WPC contiguous U.S. (CONUS) medium range forecasters.  The Alaska forecaster then uses the available model guidance and meteorological reasoning to depict the most likely scenario for days 4-8.   That meteorologist then composes a forecast discussion outlining deterministic and ensemble model differences, preferences and trends.   In addition, within the discussion the forecaster communicates confidence level, forecast uncertainty and any significant weather expected in the forecast period.


Model Diagnostics

The WPC model diagnostic meteorologist prepares the Model Diagnostic Discussion which evaluates the NAM and GFS along with other operational model and ensemble guidance for each significant system affecting the continental U.S. through 84 hours from model initialization. This discussion emphasizes model differences and preferences, with an evaluation of NAM/GFS analyses if there are significant errors and a review of model trends and biases if appropriate.  There are two issuances during each of the day and night shifts corresponding to the arrival of latest model data.

The following table shows the deadline and content for each issuance.

Issuance Time Content
0445Z/1645Z Evaluate NAM and GFS initializations
Compare NAM/GFS and other available model/ensemble guidance
Review model trends and biases as appropriate Discuss model preferences
0645Z/1845Z Evaluate the ECMWF/UKMET/Canadian global models relative to other current guidance
Finalize model 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.


Surface Analysis Products

The 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.

Analysis Time Issuance Time Web Posting
00Z 0127Z 0147Z
03Z 0430Z 0450Z
06Z 0733Z 0753Z
09Z 1028Z 1048Z
12Z 1329Z 1349Z
15Z 1635Z 1655Z
18Z 1938Z 1958Z
21Z 2230Z 2250Z

PLEASE NOTE:  The Pacific Ocean analyses (East and West Pacific) are prepared by NCEP's Ocean Prediction Center


Probabilistic Heavy Snow/Icing Forecasts

PRODUCT DELIVERY SCHEDULE

The WPC Winter Weather Desk (WWD) is staffed two shifts a day from September 15 through May 15.  The WWD forecaster routinely releases updated forecasts twice daily at 0900Z and 2100Z (4am/pm EST or 5am/pm EDT respectively). Forecasts may be updated if warranted by rapidly changing situations.

PROBABILITY GRAPHICS FOR SNOW AND FREEZING RAIN

These graphics indicate the probability (potential) for a location to receive specific thresholds of accumulated snow or ice. 

  • Snowfall - closed lines represent the probability (slight, moderate, and high) that enclosed areas will receive equal to or greater than a specific threshold accumulation (4", 8" or 12") of snowfall in a 24 hour period.
  • Freezing Rain - depicts the probability in the same manner and time period as snowfall, but with an accumulation threshold of .25" (one quarter of an inch) of  freezing rain.
Note the 4" threshold on the Snowfall Probability Graphic is drawn only for elevations less than 7,500 feet.  Elevationcriteria is not imparted for the 8" and 12" thresholds. 

CAUTION ! The probability contours may appear to inordinately expand, contract or "jump" geographically after a scheduled update.  This is partially due to the frequency which the products are updated.  The "new" 24 hour period covers the last 12 hours of the previous issuance AND the next 12 hours. Additionally two model cycles have passed since the last scheduled issuance.

Specific (deterministic) accumulations for a particular location in the United States can be obtained via the National Weather Service home page.  Note, at this site you will have to click the GRAPHICAL FORECAST tab prior to clicking a location on the map.

The probabilistic graphics combined with the deterministic forecasts provide a user both the most likely amount expected from an event and the potential the event will produce accumulations in excess of specific thresholds.

PROBABILITY LEGEND

The probability thresholds used are defined as follows:

  • SLGT - 10% to 40% chance of occurrence within the outlined area.
  • MODERATE (MDT) - 40% to 70% chance of occurrence within the outlined area.
  • HIGH - 70% chance or greater of occurrence within the outlined area.
At times the forecasters may use only one or two isolines for the forecast. This simply implies slight or slight to moderate probability for the forecasted parameter. 

To gain further insight into this forecast, please read the Heavy Snow Discussion (HSD) that accompanies these graphical products.


LOW TRACKS GRAPHIC

These graphics depicts the forecast location of significant surface lows impacting the 48 contiguous United States in 12 hour increments out to 72 hours into the future.  It is provided in two formats,  non-technical and technical.

  • The non-technical version depicts the low position and track forecast by the NCEP WPC meteorologist in white.  Each low position is accompanied by a lead time (Eastern Time).  The circle around each low represents a 75% probability the observed low will be located within the circle. Note: The probability is derived using previous season's verification data. For reference, existing surface lows are depicted with a red marker without yellow circles. 
  • The technical version depicts the low position and track forecast by the NCEP WPC meteorologist in black.  Each low is accompanied by a forecast central pressure. Additionally there are no less than 35 different computer model forecasts of low position for a given lead time available to the WPC forecaster - these are depicted with symbols.  Both the central pressure and computer model forecasts are color coded according to lead time (Universal Time).  Together, the WPC forecast position of the low and computer generated position provide a user both the preferred position and track of the low and a sense of the uncertainty with the forecast.
  • For reference, existing surface lows are depicted with a red marker.  Surface lows can also be found on the WPC Surface Analysis. One can see the current location surface lows and the forecast path of both existing surface lows and surface lows expected to develop within three days time.
Note - winter weather is not always associated with significant surface lows.


Short Range Forecasts

Product Issuance Time
6 and 12 hour forecasts 0200Z (Night Shift)
1400Z (Day Shift)
18 and 24 hour forecasts 0430Z (Night Shift)
1630Z (Day Shift)
30, 36, and 48 hour forecasts 0730Z (Night Shift)
1930Z (Day Shift)
60 hour forecast 0800Z (Night Shift)
2000Z (Day Shift)
Discussion 0900Z (Night Shift)
2100Z (Day Shift)

The short range meteorologist prepares 6 through 60 hour forecasts for the continental U.S., southern Canada, and northern Mexico.   These products are issued twice daily using numerical model output from the National Weather Service's (NWS) Global Forecast System (GFS) and North American Mesoscale model (NAM), as well as guidance from the European Centre for Medium-Range Weather Forecasts (ECMWF), the United Kingdom's Meteorology Office (UKMET), the Meteorological Service of Canada, including ensembles.   Coordination with the surface analysis, model diagnostics, quantitative precipitation, winter weather, and tropical forecast desks is also performed during the forecast process.  

The short range forecast products include surface pressure patterns (isobars), circulation centers and fronts for 6-60 hours, and a depiction of the types and extent of precipitation that are forecast at the valid time of the chart.  The primary goal is to depict accurately the evolution of major weather systems that will affect the continental U.S. during the next 60 hours.   In addition, discussions are written on each shift and issued with the forecast packages that highlight the meteorological reasoning behind the forecasts and significant weather across the continental United States.

Please note that at this time isobars are not included on the 6-hour forecast and precipitation is not included on the 60-hour forecast chart.


International Desks

Please click here to find out more about this WPC function


Storm Summaries

Storm summaries provide both a summary of the significant weather which has occurred, and an WPC general forecast of the storm system over the next 1 to 2 days. Storm summaries serve as a central source for storm information which would otherwise have to be gleaned from a number of NWS Forecast Office websites.

Storm summaries are issued for significant large-scale storms which:

  • Affect multiple NWS Forecast Office areas of responsibility
  • Are likely to be of media interest
  • Impact large population areas, or major transportation systems, or otherwise make a significant impact upon the nation's or a region's commerce
  • Are usually snow and/or ice storms, but which may be rainfall events if they are causing widespread flash flooding, mudslides, etc.
If two or more separate storm systems are occurring simultaneously, a storm summary is issued for each individually.


Tropical Public Advisories

The WPC will issue public advisories after the National Hurricane Center (NHC) discontinues its advisories on subtropical and tropical cyclones that have moved inland, but still pose a threat of heavy rain and flash floods in the conterminous United States or adjacent areas within Mexico which affect the drainage basins of NWS River Forecast Centers. The last NHC advisory will normally be issued when winds in an inland tropical cyclone drop below tropical storm strength, and the tropical depression is not forecast to regain tropical storm intensity or re-emerge over water. WPC advisories will terminate when the threat of flash flooding has ended.


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Page last modified: Thursday, 14-Aug-2014 14:29:07 UTC