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 |
