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Missoula, Montana
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National Weather Service Missoula Montana

FORECASTS  

The National Weather Service forecasts utilize a standard terminology to describe the expected weather conditions. This page explains the terminology used. Missoula's forecast area encompasses central Idaho and western Montana. This area is broken down in segments (zones) based on either terrain or climatic regimes. The map to the right shows the zones in Missoula's forecast area and their associated names are listed below.

NWS Missoula Forecast Zones


Western Montana Zones
  1   Kootenai / Cabinet Region
  2   West Glacier Region
  3   Flathead / Mission Valleys
  4   Lower Clark Fork Region
  5   Missoula / Bitterroot Valleys
  6   Bitterroot / Sapphire Mountains
  7   Butte / Blackfoot Region
43   Potomac / Seeley Lake Region

Central Idaho Zones
  5   Northern Clearwater Mountains
  6   Southern Clearwater Mountains
  7   Orofino / Grangeville Region
  8   Lower Hells Canyon / Salmon River Region
  9   Western Lemhi County
10   Eastern Lemhi County

PRECIPITATION
Uncertainty Terms
Indicate the percent chance of measureable (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.
Term Coverage
Isolated 10-20%
Scattered 30-50%
Likely 60-70%
No term used 80-100%
 
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.

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

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

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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Missoula Weather Forecast Office
6633 Aviation Way
Missoula, MT 59808-9381

Tel: (406) 329-4840

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