General Forecast Terminology

Forecasts for sky cover, temperatures, and winds are the core elements of weather information disseminated by the National Weather Service on a routine basis. Listed below are descriptions of regularly used weather terms that should aid in a better understanding of their meaning.

SKY CONDITION

Describes the predominant/average sky condition based upon tenths of the sky covered by opaque (not transparent) clouds.

Sky Condition

Cloud Coverage

Cloudy 8/8 Opaque Clouds
Mostly Cloudy, or Considerable Cloudiness 6/8 to 7/8
Partly Cloudy, or Partly Sunny 3/8 to 5/8
Mostly Clear, or Mostly Sunny 1/8 to 2/8
Clear, or Sunny 0/8 Opaque Clouds

TEMPERATURES

Used to describe maximums and minimums throughout a 12 hour period.

Description Meaning
Near 40 approaching 40 or a range of temperatures from 38 to 42
Around 85 a range of temperatures from 83 to 87
Lower 50's temperatures of 50,51,52,53,54
Middle 70's temperatures of 73,74,75,76,77
Upper 30's temperatures of 36,37,38,39

WINDS

Used to describe the prevailing direction from which the wind is blowing, with speeds given in miles per hour. The numbers may vary in other parts of the country due to such variables as terrain and elevation.

Sustained Wind Speed

Descriptive Term

0 - 5 mph Light, or light and variable

5-15 mph

None used

15-25 mph

Breezy (mild temperatures) Brisk (cold temperatures) Blustery (cold and with frequent gusts)

20-30 mph

Windy

30-40 mph

Very windy

40 mph or greater

Strong, dangerous, damaging. High wind warning required.

PRECIPITATION PROBABILITIES

The following table shows precipitation probabilities used in National Weather Service forecasts and a brief explanation of each. Technically, the Probability of Precipitation (PoP) is defined as the likelihood (expressed as a percent) of a measurable precipitation event at any give point within the area covered by the zone forecast during a specified time.  Measurable precipitation is defined as equal to or greater than .01 inch or .2 mm. At times, some NWS forecasters will use "occasional" or "periods of" to describe a precipitation event that has a high probability of occurrence, i.e., they expect any given location in a forecast zone area to most likely have precipitation, but it will be of an "on and off" nature.

PoP Percent Expressions of Uncertainty Areal Qualifiers
10 percent slight chance or none isolated or none
20 percent slight chance isolated
30-40-50 percent chance scattered
60-70 percent likely numerous
80-90-100 percent (none used) (none used)

GENERAL TIME PERIODS

The terms listed below are used in National Weather Service forecasts to delineate time periods in in zone forecast products.

Time Period

Valid For:

Today 6:00 a.m. until 6:00 p.m
Tonight 6:00 p.m. until 6:00 a.m
This Morning 6:00 a.m. until around noon
This Afternoon around noon until 6:00 p.m
This Evening 6:00 p.m. until midnight

 Wind Chill Information
 Heat Index Information


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