You may see terms in a National Weather Service Zone Forecast that might not be easy to understand. The following defines much of the terminology we use in a Zone Forecast Product.
Technically, the Probability of Precipitation (often referred to as a "POP") is defined as the likelihood of occurrence (in percent) of a measurable amount of liquid precipitation (or water equivalent of frozen precipitation) during a specified period of time at any given point in the forecast area.
The following are precipitation probabilities used by the National Weather Service.
|POP Percentage||Expression/Uncertainty||Areal Qualifiers|
|10 Percent||ISOLATED or None||ISOLATED or None|
|20 Percent||SLIGHT CHANCE||ISOLATED|
|80-100 Percent||(none)||OCCASIONAL or
Forecasts normally include a sky condition unless it is implied from another part of the forecast. Below are terms we use to describe the sky condition:
|Descriptive Term||Predominant or Average Cloud Cover|
|CLEAR or SUNNY||No clouds|
|MOSTLY SUNNY or MOSTLY CLEAR||1/8 to 2/8 clouds|
|PARTLY CLOUDY or PARTLY SUNNY||3/8 to 5/8 clouds|
|MOSTLY CLOUDY (sometimes CONSIDERABLE CLOUDINESS)||6/8 to 7/8 clouds|
Each Zone Forecast conditions three periods of wind information. The direction given is the direction from which the wind blows. Speeds are rounded to the nearest 5 mph, and often a range is given.
For speeds less than 5 mph, we often say "LIGHT WIND."
For speeds of 15-25 mph, we often say "BREEZY."
For speeds of 20-30 mph, we often say "WINDY."
For speeds of 30-40 mph, we often say "VERY WINDY."
For speeds greater than 40 mph, we often say "HIGH," "STRONG," OR "DANGEROUS."