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Forecasts > Forecast Area
and Definitions
| The National
Weather Service forecasts utilize a standard terminology to describe
the expected weather conditions. This page explains the terminology
used for each forecast element in our most used forecast product, the
zone forecasts. Riverton's forecast area
encompasses central and western Wyoming.
This area is broken down in segments (zones) based on either terrain
or climatic regimes. The map below shows the
zones in Riverton's forecast area and their
associated names. |
|
All public forecasts are split
into several periods. The one to three day forecast is broken into 12
hour forecast periods. The day period is from 6 am to 6 pm (local
time) and the night period is from 6 pm to 6 am. The four to seven day
forecast consists of 24 hour forecast periods. These periods are a
calendar day from Midnight to Midnight.
If any weather watches or long term warnings are in effect, these will
be headlined before the first forecast period. Significant weather or
changes may also be headlined. |
Zone Forecast (example)
WYZ013-121100-
JACKSON HOLE-
INCLUDING THE CITIES OF...JACKSON
400 PM MDT SUN MAY 11 2003
.TONIGHT...SCATTERED RAIN SHOWERS AND THUNDERSTORMS THIS EVENING...
OTHERWISE PARTLY CLOUDY. LOWS IN THE LOWER 30S. CHANCE OF RAIN 30
PERCENT.
.MONDAY...PARTLY CLOUDY. A CHANCE OF RAIN SHOWERS IN THE MORNING...
THEN A CHANCE OF SHOWERS AND THUNDERSTORMS. HIGHS IN THE UPPER 50S.
CHANCE OF RAIN 30 PERCENT.
.MONDAY NIGHT...MOSTLY CLOUDY. A CHANCE OF SHOWERS AND THUNDERSTORMS
IN THE EVENING...THEN A CHANCE OF RAIN SHOWERS. LOWS IN THE MID 30S.
CHANCE OF RAIN 30 PERCENT.
.TUESDAY...MOSTLY CLOUDY WITH A CHANCE OF RAIN SHOWERS AND
THUNDERSTORMS. HIGHS IN THE MID 50S. CHANCE OF RAIN 30 PERCENT.
.TUESDAY NIGHT...PARTLY CLOUDY. LOWS IN THE MID 30S.
.WEDNESDAY...PARTLY CLOUDY. HIGHS IN THE LOWER 60S.
.WEDNESDAY NIGHT...PARTLY CLOUDY. LOWS IN THE LOWER 30S.
.THURSDAY...PARTLY CLOUDY. A CHANCE OF SHOWERS AND THUNDERSTORMS FROM
NOON ON. HIGHS IN THE LOWER 60S.
.FRIDAY AND SATURDAY...PARTLY CLOUDY WITH A CHANCE OF SHOWERS AND
THUNDERSTORMS. LOWS IN THE UPPER 30S AND HIGHS AROUND 60.
.SUNDAY...PARTLY CLOUDY. LOWS IN THE MID 30S AND HIGHS IN THE UPPER
50S.
$$
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|
| PRECIPITATION |
Uncertainty Terms
Indicate the percent chance of measurable (0.01 inches) precipitation
occurring anywhere in the forecast zone or area. |
| Term |
Probability |
| Slight Chance |
10-20% |
| Chance |
30-50% |
| Likely |
60-70% |
| no term used |
80-100% |
Descriptive
Terminology
Give further detail to the timing and type of precipitation forecasted.
Duration Terms include: Occasional, Periods, Frequent, Brief, etc.
Intensity Terms include: Very Light, Light, Heavy (Lack of an
intensity term is moderate intensity)
|
Areal Qualifiers
Indicate precipitation will occur in the forecast zone or area, but will
only cover a certain percentage of the zone or area. |
| Coverage |
Term |
| 10-20% |
Isolated |
| 30-50% |
Scattered |
| 60-70% |
Numerous |
| 80-100% |
no term used |
Combining
Terminology
Intensity terms can be combined with duration terms, uncertainty terms
or areal qualifiers. Some common combinations - scattered light showers,
periods of heavy rain, chance of heavy snow
Duration terms can NOT be combined with uncertainty terms or areal
qualifiers. Uncertainty terms and areal qualifiers can NOT be combined
with each other. A few INCORRECT combinations - chance of scattered
showers, chance of occasional rain, periods of scattered showers.
|
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| SKY CONDITIONS |
| |
| Term |
Cloud Cover |
|
Weather observations and aviation
forecasts use areal terms, such as clear, few, scattered, broken or
overcast. |
| Cloudy |
8/8 |
| Mostly Cloudy |
6/8 - 7/8 |
Partly Cloudy or
Partly Sunny |
3/8 - 5/8 |
Mostly Clear or
Mostly Sunny |
1/8 to 2/8 |
| Clear or Sunny |
less than 1/8 |
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| TEMPERATURE |
| |
Specific
|
|
Given for larger towns and
listed below narrative forecast.
Specific forecasted highs and lows at NWS observation sites.
|
Ranges
|
|
Listed within the narrative
forecast, either a number or descriptive range (see table below),
expected high or low within a zone(s).
|
Change
|
|
Descriptive terms are used
when the temperature change from one day to another is within certain
limits (see table below).
|
| Range |
Defined |
|
Change |
Description |
| lower 50s |
50, 51, 52, 53, 54 |
|
0 to 7 F |
no mention |
| mid 50s |
53, 54, 55, 56, 57 |
|
7 to 20 F |
warmer, colder, cooler |
| upper 50s |
56, 57, 58, 59 |
|
20 F or greater |
much warmer, colder |
| 60s |
60 through 69 |
|
below zero |
very cold |
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| WIND |
| |
Speed
Numeric (first two forecast periods) or descriptive (third forecast
period and beyond). |
| Numeric |
Descriptive |
| 15 to 25 mph |
Breezy (mild), Brisk (cold) |
| 20 to 30 mph |
Windy |
| 30 to 40 mph |
Very Windy |
Direction
An eight point compass (N, NE, E, SE, S, SW, W, NW) is used.
|
Utilization
Winds are only mentioned in the zone forecasts, when expected to be
least 15 mph. Local mountain and valley breezes are not mentioned.
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