Weather Forecast Terminology

Anatomy of a Forecast
Information supplied by the National Weather Service

The National Weather Service issues forecasts for sky condition, temperature, wind, and precipitation probability on a routine basis. Because the weather is always changing, the terminology used in these forecasts is also quite variable. Listed below are descriptions of regularly used weather terms that should give you a better understanding of each forecast.

SKY CONDITION
The sky condition describes the predominant/average sky condition based on eighths of the sky covered by opaque (not transparent) clouds. If a high probability of precipitation (60% or greater) is expected, then the sky condition may be omitted since it is inferred from the precipitation forecast.

TEMPERATURE
The temperature in a forecast is used to describe the forecast maximum and minimum temperature, or in some cases, the temperature expected at a specific time.

WIND
The wind describes the prevailing direction from which the wind is blowing, with speeds in miles per hour. Wind velocity is included in the first two periods of a zone forecast.

PRECIPITATION PROBABILITY
The Probability of Precipitation (POP) is defined as the likelihood of occurrence (expressed as a percent) of a measurable amount of liquid precipitation (or the water equivalent of frozen precipitation) during a specified period of time at any given point in the forecast area. Measurable precipitation is equal to or greater than 0.01”. Unless specified otherwise, the time period is normally 12 hours. The forecast area, or zone, is generally considered to be a county. NWS forecasters use such categorical terms as occasional, intermittent, or periods of to describe a precipitation event that has a high probability of occurrence (80% +) but is expected to be of an “on and off” nature.