829
FXUS65 KMSO 210927
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
327 AM MDT WED OCT 21 2026
DISCUSSION
KEY MESSAGES:
- MILD DAYTIME TEMPERATURES THROUGH THURSDAY.
- PATCHY VALLEY FOG AROUND SUNRISE EACH MORNING.
- SIGNIFICANT WEATHER CHANGE COMING THURSDAY NIGHT INTO FRIDAY.
MILD DAY-TIME TEMPERATURES WILL CONTINUE ACROSS THE NORTHERN
ROCKIES THROUGH THURSDAY AS HIGH PRESSURE REMAINS IN CONTROL.
STABLE CONDITIONS UNDER THE RIDGE ARE PROMOTING THE DEVELOPMENT
OF DAILY VALLEY INVERSIONS AND TRAPPED COLD AIR, WITH PATCHY DENSE
FOG. AFTERNOON TEMPERATURES WILL RUN AROUND 10 DEGREES ABOVE
NORMAL FOR THIS TIME OF YEAR.
A SIGNIFICANT CHANGE REMAINS ON TRACK LATE THURSDAY INTO FRIDAY, AS
A LOW PRESSURE SYSTEM AND COLD FRONT TRACKS ACROSS THE REGION.
COLDER TEMPERATURES AND WIDESPREAD PRECIPITATION, FOCUSED ALONG
AND SOUTH OF THE INTERSTATE 90 CORRIDOR AND ALONG THE DIVIDE IN
NORTHWEST MONTANA ARE THE MAIN STORY. PRECIPITATION AMOUNTS HAVE
TRENDED HIGHER OVER THE LAST 48 HOURS, AS MODEL GUIDANCE HAS COME
INTO STRONGER CONSENSUS FOR A MID-LEVEL LOW TO TRACK ALONG THE
DIVIDE IN SOUTHWEST MONTANA BY FRIDAY MORNING. WIDESPREAD
PRECIPITATION WILL WRAP AROUND THE WEST-NORTHWEST AREA OF THIS LOW
POINTING TOWARDS THE HIGHEST PRECIPITATION AMOUNTS (0.75-1.50
INCHES) ALONG THE DIVIDE ACROSS MOUNTAIN RANGES IN SOUTHWEST
MONTANA. AS DISCUSSED PREVIOUSLY, 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
ACROSS HIGHER PEAKS ALONG THE DIVIDE, WHERE SEVERAL INCHES OF SNOW
MAY FALL ABOVE 7,000 FEET.
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
HIGH PRESSURE WILL CONTINUE TO BRING STABLE
CONDITIONS. VALLEY INVERSIONS AND COLD AIR POOLS WILL SET THE
STAGE FOR PATCHY 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 KGPI AND KMSO. THE
PROBABILITY OF DENSE FOG IMPACTS AT THESE TERMINALS IS GENERALLY
LESS THAN 10 PERCENT, BUT CAN NOT BE RULED OUT.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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