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.
PRECIPITATION
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 |
0 Percent |
None |
None |
10 Percent |
ISOLATED or None |
ISOLATED or None |
20 Percent |
SLIGHT CHANCE |
ISOLATED |
30-50 Percent |
CHANCE |
SCATTERED |
60-70 Percent |
LIKELY |
NUMEROUS |
80-100 Percent |
(none) |
OCCASIONAL or
PERIODS OF |
SKY CONDITION
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 |
CLOUDY |
8/8 clouds |
Also used:
INCREASING CLOUDS
DECREASING CLOUDS |
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WIND
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."
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