National Weather Service - San Francisco/Monterey Bay Area - glossary
......NWS
TERMINOLOGY
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PRECIPITATION
PROBABILITY of PRECIPITATION (POP) is
the likelihood of occurrence (expressed as a percent) of a precipitation
event at any given point in the forecast area. The NWS uses two different
methods to indicate the chance of precipitation for a specific area: numerical
or in non- numerical terms. The "Expression of Uncertainty" category is
used for widespread precipitation and the "Equivalent Areal Coverage"
for convective (i.e., showery) events. Below is a table of these two methods
with the corresponding POP.
POP |
Expression of Uncertainty |
Equivalent Areal Coverage |
0% |
None used |
None Used |
10% |
Slight Chance |
Isolated or none used |
20% |
Slight Chance |
Isolated |
30-40% |
Chance |
Scattered |
60-70% |
Likely |
Numerous or none used |
80-100% |
None |
None used |
There are other qualifying terms which are used with the above non-numerical
expressions. For example:
For duration - brief, occasional, intermittent, frequent.
For intensity:
Very Light |
< .01 inch per hour |
Light |
.01 to .10 inch per hour |
Moderate |
.10 to .30 inch per hour |
Heavy |
greater than .30 inch per hour |
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WIND TERMINOLOGY
WIND DIRECTION and SPEED A forecast wind
(direction and speed) is included in the first three periods of the forecast.
The wind is included in the fourth period if considered significant.
1. Wind direction is the direction where the wind is coming FROM and
is based on an 8-point compass (NE, E, SE, etc.). Light wind (usually
5 mph or less) will be handled in the following ways:
LIGHT SOUTH WINDS (if direction is known),
LIGHT AND VARIABLE WINDS , or
LIGHT WINDS (where "light" implies a variable wind direction).
2. Wind speed will be given in miles per hour. Following is a list of
terms sometimes used to describe the wind speed.
Speed range
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Terms
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0-5 mph |
light or light and variable |
5-15 mph |
none used |
15-25 mph |
none used or breezy for mild weather |
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brisk for cold weather |
20-30 mph |
breezy (mild weather), brisk (cold weather) |
25-35 mph |
windy |
30-40 mph |
very windy |
40 mph or greater |
strong, damaging, dangerous, high |
Note: A forecast can contain a peak wind speed in gusty situations.
For example, "NORTHWEST WIND 20 TO 30 MPH WITH OCCASIONAL GUSTS TO 40
MPH.")
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TEMPERATURE TERMINOLOGY
Numerical temperature values are represented in NWS forecasts in four
ways:
1. "Near," "around," or "about" a specific value rounded to the nearest
five zero. Above 100°F or below 10°F, any number will be used.
For example:
NEAR 40, AROUND 15, ABOUT 85, or NEAR 106.
2. A general range where the terms are defined by the following:
LOWER 50's (50 - 54)
MID 50's (53 - 57)
UPPER 50's (56 - 59)
50's (50 - 59)
3. A specific range rounded to the nearest five or zero (except ranges below
10°F or above 100°F, any number may be used). For example, 70 to
75 or 102 to 108.
4. Specific numbers for site-specific locations: TRI-CITIES 70/50/72
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SKY COVER TERMINOLOGY
Predominate Sky Condition
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Daytime Terminology
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Day or Night Terminology
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0/8 Opaque Clouds |
Sunny
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Clear
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1/8 - 2/8 Opaque Clouds |
Mostly Sunny
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Mostly Clear
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3/8 - 5/8 Opaque Clouds |
Partly Sunny
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Partly Cloudy
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6/8 - 7/8 Opaque Clouds |
Mostly Cloudy
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Mostly Cloudy
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8/8 Opaque Clouds |
Cloudy
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Cloudy
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HEAT INDEX
The NWS has devised the "HEAT INDEX" (HI), sometimes called the "apparent
temperature." The HI is the temperature the body feels when the heat and
humidity are combined.
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......FIRE WEATHER TERMINOLOGY |
- Fuel Moisture:
The quantity of moisture in fuels expressed as a percentage of the weight when thoroughly dried at 212 degrees Fahrenheit. Also referred to as fuel moisture content.. Fuel moisture observations are generally for the 10-hour time lag fuels (medium-sized roundwood 1/4" to 1" in diameter)
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US Dept of Commerce
National Oceanic and Atmospheric Administration
National Weather Service
San Francisco/Monterey Bay Area Weather Forecast Office
21 Grace Hopper Ave, Stop 5
Monterey, CA 93943-5505
Tel: (831)-656-1725
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