In the National Weather Service’s January 2012 weather forecast for the USA, issued half a month ahead, NWS is anticipating higher-than-average temperatures in the East of the Country, and lower temperatures in the West. The forecast for precipitation is below-average in the South, with above-average or near-normal further North. The three month outlook for January, February, and March is similar.
National Weather Service Forecast products
NWS forecast products are outlined in this figure. Starting from the short timescale, NWS issues watches and warnings associated with hurricanes and floods.
In the summer, it also issues surface ultraviolet forecasts to warn people of the dangers of excessive exposure to sunshine. These forecasts are based on ozone forecasts and the solar zenith angle, which depends on the latitude and time of year.
Weather Forecasting Projections
The main forecasting suite covers the range 0-48 hours and 3-7 days. These are detailed forecasts determined by a computer model of the atmosphere, and are published complete with meteorological charts. The forecasts rely on receipt of observations from around the world to initialize the reports. Because time is of the essence, there is a cut-off point at which no more data are incorporated, and the forecast is started. For the medium range forecast (3-7) days, the same procedure is followed, except that there is more time available to collect data for the initial forecast date.
Forecast accuracy gets steadily worse as the time from the start of the forecast increases. Forecasts 0-48 hours are extremely reliable. After that period, one of the main causes of forecast error is the timing of events, so errors tend to accumulate over time. Forecast degradation can be reduced with a better starting point, and from improved or more comprehensive observations.
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