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The Forecast Process - creating the forecast products
The NWS issues a comprehensive package of forecast products to support
a variety of users twice a day. In addition, a late morning and evening update are
typically issued. Additional updates are produced as conditions warrant. Although text forecasts
have been the primary means of product dissemination for many years, the NWS has converted
many of its forecast products to a digital, gridded format. Each of the
123 NWS Weather Forecast Offices send their gridded forecasts to a national
server to be compiled in the National Digital Forecast Database (NDFD). The NDFD
is a national gridded forecast database of sensible weather elements including maximum and minimum
temperature, humidity, cloud cover, probability of precipitation, weather type,
wind direction, and wind speed produced by local forecast offices. Most of the primary forecast products issued by the NWS including
those for the public, fire weather, and marine users originate via the gridded forecast database.
Once a meteorologist has thoroughly reviewed the current weather situation and has
conceptualized the forecast, it is time to make the forecast. Forecasters will write an Area
Forecast Discussion (AFD) which is a narrative text product that explains the meteorological
reasoning behind the forecast. The AFD was originally intended as a coordination
tool between adjacent forecast offices but it has also evolved into a
communication tool for our users including local meteorologists, the media, emergency managers,
spotters, and the public.
Forecasters use a program called GFE (Graphical Forecast Editor) to create the forecast. GFE allows the forecaster to
draw "grids" of the expected weather conditions for various forecast parameters including
high and low temperatures, relative humidity, wind, sky cover, probability of
precipitation, and weather type. Data from computer models and current observations
are used to assist this process. The forecast parameters are stored in a local
database. The database is then shared among neighboring offices which
allows forecasters to collaborate with their neighbors, to make sure
there are no drastic changes across NWS coverage areas.
Once the forecasters have created the gridded forecasts in their local database
and the forecast has been collaborated and quality controlled, the forecast is then placed in the
official database. Formatters within the GFE program are used to create text products from the
official database. Some of the text products generated from the formatters include the
Zone Forecast Product (ZFP),
Area Forecast Matrix (AFM),
and Point Forecast Matrix (PFM).
The text products are then transmitted to the public, media, emergency managers, and other users.
Other programs create
graphical
images from the official database for display on the local NWS websites.
Finally, the official database is then transmitted to the NDFD where it is mosaiced with the official
database from other NWS offices to form the NDFD.
The image to the right, is the current forecast high temperature for the first day of the current forecast
across the Mid Atlantic region
from the NDFD. The same data can also be viewed in detail across
the NWS Raleigh CWA.
Additional details on the National Digital Forecast Database (NDFD) are available at
www.weather.gov/ndfd/.
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