Home > 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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