Published: 2008-10-08 09:29:25
Updated: 2008-10-08 09:29:25
Posted October 8, 2008
By John Green
MIKE MOSS SAYS: John, When you select a specific location and request hourly forecast details (actually given at three-hour intervals), you are taken away from our internally generated WeatherCenter forecast and routed to output that is drawn from the National Weather Service's National Digital Forecast Database, which can be queried by zip code or City, State. This is noted on the page just above the hourly forecast listing, where a header says "National Weather Service Hourly Forecast for ZZZZZ" where ZZZZZ indicates the requested zip code location.
I can't speak to the specific wind direction errors you've noted since I don't know when they occurred, but in general wind directions are well forecast when there are well-defined pressure patterns in place, and more subject to variability and error when winds are light and pressure gradients are weak. In thse cases, the general direction and speed forecast often turns out to be on target for a day-long average, but the effects of local convection and passing eddies in the flow can make any particular 2-minute averaged observation (as given by the anemometer at an airport) considerably different.
One other item to note here is that since the hourly detail forecasts are from the NWS database, there may be times when our forecast differs from theirs in a way that makes the hourly details seem non-sensical. For example, suppose we are forecasting a chance of rain but they are not. Our 7-day forecast may show a drop and mention scattered showers in the text, but the hourly details may not indicate any rain through the day (or vice versa, of course). Likewise, suppose we forecast a high of 73 and they forecast a high of 76. One of the detailed forecast hours may show a temperature of 75 or 76, which will appear to conflict with our 7-day forecast high of 73.