About the National Forecast Chart

Description
The WPC National Forecast Charts provide an overview of expected weather for up to the next three days, with emphasis on certain hazardous and significant weather. They summarize forecasts from several NCEP Service Centers including the Storm Prediction Center (for severe thunderstorm and fire weather outlooks), the National Hurricane Center (for tropical storm and hurricane forecasts), and the Weather Prediction Center (for information concerning heavy rainfall, flooding, winter weather, and general weather). With overlaid frontal forecasts, these displays serve as a good overview of the expected weather for the next three days. All three days of the forecast chart are available in both English and Spanish.

Beginning in 2019, the look of the National Forecast Charts changed from a simple static image to a user-friendly and interactive map based on GIS technologies. This also allows the user the capabilities to turn on and off individual hazards and weather areas. A static map also continues to be automatically generated for downloading purposes.

Purpose
The charts are intended for use by anyone who needs a non-technical display of the expected weather including the general public, the media, and the emergency management community. They show the large-scale weather features and associated significant weather. These charts are especially useful to travelers or others needing a big picture forecast. They are not intended to provide detailed local forecasts for any particular area. See http://weather.gov/ for access to detailed local NWS forecasts and warnings.

Availability and Product Valid Times
The Day 1 (today's) National Forecast Chart is prepared twice daily at the WPC. The initial product is issued by 5 a.m. EST/EDT, with an update provided by 2200 UTC (5 p.m. EST).

The Day 2 and Day 3 National Forecasts are prepared once daily and issued by 5 a.m. EST/EDT.

Valid times of the features displayed in these products vary depending upon issuance time and the particular weather phenomenon of interest. Table 1 below provides detailed information regarding the valid times for these forecasts.

Feature	Valid Times for Day 1 - Today's Forecast	Valid Times for Day 2 (Tomorrow) and Day 3 Forecasts
Surface features such as highs, lows, and fronts	AM issuance: 1200 UTC (7 a.m. EST)	AM issuance: 1200 UTC (7 a.m. EST) tomorrow or 1200 UTC Day 3.
	PM issuance: 0000 UTC (7 p.m. EST)
General precipitation areas	AM issuance: 24-hour period starting at 1200 UTC (7 a.m. EST) of the current day.	AM issuance: 24-hour period starting at 1200 UTC (7 a.m. EST) tomorrow or 1200 UTC Day 3.
	PM issuance: 12-hour period from 0000 UTC to 1200 UTC (7 p.m.-7 a.m. EST)
Severe weather	AM issuance: 24-hour period starting at 1200 UTC (7 a.m. EST) of the current day.	AM issuance: 24-hour period starting at 1200 UTC (7 a.m. EST) tomorrow or 1200 UTC Day 3.
	PM issuance: 16-hour period starting at 2000 UTC (3 p.m. EST) of the current day.
Critical Fire Weather	AM issuance: 24-hour period starting at 1200 UTC (7 a.m. EST) of the current day.	AM issuance: 24-hour period starting at 1200 UTC (7 a.m. EST) tomorrow or 1200 UTC Day 3.
	PM issuance: 16-hour period starting at 2000 UTC (3 p.m. EST) of the current day.
Winter weather forecasts	AM issuance: 24-hour period starting at 1200 UTC (7 a.m. EST) of the current day.	AM issuance: 24-hour period starting at 1200 UTC (7 a.m. EST) tomorrow or 1200 UTC Day 3.
	PM issuance: 12-hour period starting at 0000 UTC (7 p.m. EST) of the current day.
Flash flooding forecasts	AM issuance: 24-hour period starting at 1200 UTC (7 a.m. EST) of the current day.	AM issuance: 24-hour period starting at 1200 UTC (7 a.m. EST) tomorrow or 1200 UTC Day 3.
	PM issuance: From issuance time through 1200 UTC (7 a.m. EST tomorrow)

Table 1. Valid times for various features shown on the National Forecast Charts.

Basis of the National Forecast Charts
The National Forecast Charts depict the location of frontal systems and pressure centers over the continental United States and include several weather parameters derived from forecast charts prepared by other NCEP Service Centers. See Table 2 below for the sources of the forecasts.

Weather Feature	Origin and Thresholds
Severe Thunderstorms	SPC convective outlook slight risk contour (chance of severe weather within 25 miles of a certain point).
Flash flooding	WPC excessive rainfall outlook slight risk contour (10-20% chance of exceeding flash flood guidance within 25 miles of a certain point).
Heavy Snow	WPC winter weather probabilistic forecasts showing at least a 30% chance of meeting or exceeding local winter storm warning criteria
Freezing Rain	WPC freezing rain forecasts of at least 0.01" of ice produced by the WPC winter weather desk
Critical Fire Weather	The critical fire weather threat polygon from the SPC Fire Weather Outlooks
General Weather	WPC Quantitative Precipitation Forecasts for coverage, and weather type from the NWS NDFD forecasts
Fronts and low/high pressure areas	WPC short-range public products
Tropical Systems	Latest NHC forecast points valid at the same time as the fronts

Table 2. Sources of forecasts depicted on the National Forecast Charts.

See http://www.wpc.ncep.noaa.gov/html/fntcodes2.shtml for an explanation of the symbols used to depict frontal systems on the National Forecast Charts and WPC surface charts.

Feedback
We are always seeking to improve our products based on user feedback. Comments concerning this and other WPC products can be sent through the “Contact Us” section of the WPC webpage at http://www.wpc.ncep.noaa.gov/mail_webmaster.

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