Time scales are concerned with forecasting based on time parameters. They are used by the National Weather Service (NWS) to describe long range forecasts compared with normal as well as to create up-to-the-minute short term forecasts.
90 DAY OUTLOOK
This time parameter is based on the general weather pattern for the few months leading up to the time that the forecast is made. This is compared with previous years in which similar weather patterns existed.
30 DAY OUTLOOK
In this outlook, meteorologists predict where the general wind flow pattern will be at 10,000 feet over a regional area and the weather conditions that the region can expect given this type of air flow. An example is when the wind is flowing north from the Gulf of Mexico. It is then considered likely that the southeastern United States will experience higher than average precipitation.
3 TO 10 DAY OUTLOOK
Called the medium and long range outlook, this general weather pattern is based more on present scientific data than the 30 and 90 day outlooks. Computer models take current surface and upper air data and project what the general weather pattern will be during this period.
SHORT RANGE FORECAST (12 TO 48 HOURS)
As computer models have become more accurate and detailed, it is easier to make short range forecasts than ever before.
THE NOWCAST
The National Weather Service (NWS) issues products concerned with weather situations that will affect an area in the very near future. The announcement at 9:00 PM that a cold front moving in will reach town by 11:30 PM is an example of a new NWS product known as the nowcast.
A tornado warning issued for a county that's in effect for the next 45 minutes is also associated with the nowcast time frame.
