262
FXUS65 KMSO 310702
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
102 AM MDT MON AUG 31 2026
DISCUSSION
KEY MESSAGES:
- CHILLY THIS MORNING WITH FROST TO HIGH- ELEVATION VALLEYS.
- A BRIEF WARM-UP WITH DRY CONDITIONS AND LOW RELATIVE HUMIDITIES EARLY
THIS WEEK.
- INCREASING THUNDERSTORM CHANCES TUESDAY AFTERNOON INTO WEDNESDAY,
GUSTY OUTFLOW WIND THREAT. NEAR-CRITICAL FIRE WEATHER RISK IN
SOUTHWEST MONTANA.
- AN ACTIVE, COOLER WEATHER PATTERN WITH ABOVE-NORMAL PRECIPITATION
PROBABILITIES LATE THIS WEEK.
TODAY THROUGH TUESDAY: OPTIMAL RADIATIONAL COOLING UNDER CLEAR
SKIES, LIGHT WINDS, AND A DRY AIR MASS WILL YIELD CHILLY MORNING
TEMPERATURES TODAY. HIGH PROBABILITIES (70-90%) FOR FROST EXIST
IN THE HIGHER VALLEYS ALONG THE CONTINENTAL DIVIDE AND NORTH-
CENTRAL IDAHO, WHERE LOWS WILL DIP INTO THE UPPER 20S TO LOWER
30S. PATCHY LIGHT FROST IS ALSO POSSIBLE IN TYPICAL COLD SPOTS
WITHIN LOWER VALLEYS, INCLUDING THE STEVENSVILLE AREA AND THE FAR
WESTERN MISSOULA VALLEY.
A BRIEF WARMING AND DRYING TREND BEGINS TODAY INTO TUESDAY AS
HIGH PRESSURE BUILDS OVER THE NORTHERN ROCKIES. HIGH TEMPERATURES
WILL REBOUND INTO THE 80S FOR MOST VALLEYS, RUNNING ROUGHLY 10
DEGREES ABOVE SEASONAL NORMALS BY TUESDAY. BY TUESDAY AFTERNOON,
MID- LEVEL MOISTURE INCREASES FROM THE SOUTH, INITIATING SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS ACROSS IDAHO AND LEMHI
COUNTIES THAT WILL TRACK NORTHWARD. STEEP LOW-LEVEL LAPSE RATES
BENEATH HIGH STORM BASES (~10,000 FT AGL) AND A DRY SUB-CLOUD
LAYER (INVERTED-V PROFILE) WILL FAVOR STRONG OUTFLOW WINDS. HIGH-
RESOLUTION GUIDANCE INDICATES GUSTS OF 35-50 MPH, WITH A LOW
PROBABILITY (LESS THAN 5%) OF LOCALIZED SEVERE GUSTS EXCEEDING 60
MPH.
WEDNESDAY THROUGH WEEKEND: A WELL-DEFINED SHORTWAVE DISTURBANCE
WILL BRING WIDESPREAD SHOWERS AND THUNDERSTORMS WEDNESDAY
AFTERNOON AND EVENING, WITH GUSTY OUTFLOW WINDS REMAINING A
HAZARD, ESPECIALLY ACROSS SOUTHWEST MONTANA. ELEVATED TO NEAR-
CRITICAL FIRE WEATHER CONDITIONS ARE EXPECTED ACROSS SOUTHWEST
MONTANA AHEAD OF CONVECTIVE INITIATION. WETTING RAIN (> 0.10 IN)
PROBABILITIES HAVE INCREASED TO 70-90% ACROSS MUCH OF THE
NORTHERN ROCKIES, WITH A 50-70% CHANCE OF ACCUMULATIONS EXCEEDING
0.25 INCHES.
SHOWERS, ISOLATED THUNDERSTORMS, AND ELEVATED WINDS WILL PERSIST
THURSDAY AND FRIDAY BEFORE SURFACE WINDS DIMINISH INTO THE
WEEKEND. ENSEMBLE GUIDANCE SHOWS HIGH CONFIDENCE IN A LONGWAVE
TROUGH REMAINING ANCHORED OVER THE PACIFIC NORTHWEST. THIS PATTERN
MAINTAINS SOUTHWESTERLY FLOW ACROSS THE NORTHERN ROCKIES, SUPPORTING
AN ACTIVE REGIME WITH ABOVE-NORMAL PRECIPITATION PROBABILITIES
AND DAILY CONVECTIVE ACTIVITY.
AVIATION
VFR CONDITIONS AND LIGHT, DIURNALLY DRIVEN WINDS WILL
DOMINATE AS HIGH PRESSURE BRIEFLY BUILDS IN. ONE EXCEPTION WILL
BE THE POTENTIAL FOR PATCHY VALLEY FOG ACROSS NORTHWEST MONTANA
(INCLUDING KGPI) THIS MORNING BUT ANY FOG THAT DEVELOPS SHOULD
QUICKLY DIMINISH BY MID MORNING. THUNDERSTORM CHANCES AND A GUSTY
OUTFLOW WIND THREAT RETURNS ON TUESDAY AFTERNOON/EVENING.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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