048
FXUS65 KMSO 201747
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
1147 AM MDT TUE OCT 20 2026
DISCUSSION
KEY MESSAGES:
- MILD DAYTIME TEMPERATURES THROUGH THURSDAY.
- PATCHY VALLEY FOG AROUND SUNRISE EACH MORNING.
- SIGNIFICANT WEATHER CHANGE COMING FRIDAY INTO THE WEEKEND.
A BROAD RIDGE OF HIGH PRESSURE WILL CONTINUE TO BRING MILD DAYTIME
TEMPERATURES ACROSS THE NORTHERN ROCKIES THROUGH THURSDAY. STABLE
CONDITIONS UNDER THE RIDGE ARE PROMOTING THE DEVELOPMENT OF DAILY VALLEY
INVERSIONS AND TRAPPED COLD AIR, WITH PATCHY DENSE FOG. AFTERNOON
TEMPERATURES WILL CONTINUE TO RUN 10 TO 15 DEGREES ABOVE NORMAL FOR THIS
TIME OF YEAR. FORECAST MODELS SUGGEST A FEW ISOLATED SHOWERS DEVELOPING
OVER LEMHI COUNTY THIS AFTERNOON, THEN OVER SOUTHWEST AND WEST-CENTRAL
MONTANA TOMORROW AFTERNOON AND EVENING.
EXPECT A SIGNIFICANT CHANGE AS A LOW PRESSURE SYSTEM AND COLD FRONT TRACK
ACROSS THE REGION THURSDAY NIGHT INTO FRIDAY. THE FRONT WILL BRING WIND
GUSTS AROUND 20 MPH IN IDAHO AND 20 TO 35 MPH ACROSS MOST OF WESTERN
MONTANA ON FRIDAY. MOISTURE WITH THIS SYSTEM WILL MOVE NORTH FROM THE GREAT
BASIN, WITH PRECIPITATION FOCUSING ALONG AND SOUTH OF THE I-90 CORRIDOR AND
ALONG THE CONTINENTAL DIVIDE IN NORTHWEST MONTANA. MOST OF THE
PRECIPITATION WILL FALL AS RAIN AHEAD OF THE COLD FRONT, LIMITING THE
POTENTIAL FOR WINTER WEATHER IMPACTS. SNOW LEVELS WILL FALL TO AROUND 5,000
FEET FRIDAY AND LOWER OVER THE WEEKEND AS SHOWER ACTIVITY BEGINS TO
DECREASE. THEREFORE, FORECAST SNOW AMOUNTS WILL BE GENERALLY UNDER
AN INCH ACROSS THE REGION AND ABOVE 5,000 FEET. THE EXCEPTION IS
THE HIGHER ELEVATIONS OF THE FLATHEAD NATIONAL FOREST AND GLACIER
NATIONAL PARK, WHICH WILL LIKELY PICK UP SEVERAL INCHES OF SNOW
THIS WEEKEND.
THERE REMAINS CONSIDERABLE UNCERTAINTY IN THE EXTENDED FORECAST AS THE
MAJORITY OF LONG-RANGE FORECAST MODELS HAVE DIFFERENT OPINIONS ON THE
OVERALL PATTERN EARLY NEXT WEEK. TWENTY PERCENT OF THE MODELS SHOW ANOTHER
RIDGE OF HIGH PRESSURE RETURNING TO THE REGION, WITH THE OTHER MODELS
SUGGESTING A SOUTHWEST FLOW OR A COLD CANADIAN TROUGH. STAY TUNED.
AVIATION
STABLE CONDITIONS WILL CONTINUE TODAY UNDER A RIDGE OF
HIGH PRESSURE. VALLEY INVERSIONS AND COLD AIR POOLS WILL SET THE
STAGE FOR AREAS OF VALLEY FOG, PARTICULARLY NEAR LARGE BODIES OF
WATER AND RIVER SYSTEMS. THE PRIMARY PERIOD TO WATCH WILL BE FROM
21/1200-1500Z, INCLUDING TERMINAL KMSO. FOG CAN NOT BE RULED OUT
AT KGPI AS WELL, BUT THE PROBABILITY OF IMPACTS IS LESS THAN 10
PERCENT AS HIGH CLOUD COVER HAS REDUCED OVERNIGHT COOLING.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page