997
FXUS65 KMSO 250858
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
258 AM MDT SAT APR 25 2026
DISCUSSION
KEY MESSAGES:
- NEAR RECORD OR RECORD COLD TEMPERATURES FORECAST FOR SATURDAY
AND POSSIBLY SUNDAY.
- SNOW SHOWERS WILL PERSIST ALONG THE DIVIDE AND POINTS WEST
THROUGH THE WEEKEND. ROADWAYS AND MOUNTAIN PASSES COULD BECOME
SNOW-COVERED AT TIMES, ESPECIALLY OVERNIGHT AND IN THE EARLY
MORNING.
- GRADUAL WARM-UP WITH AFTERNOON SHOWERS IS EXPECTED TUESDAY AND
WEDNESDAY. FROSTY MORNINGS ARE POSSIBLE.
- HIGH TEMPERATURES REACHING THE 70S BY FRIDAY ACROSS NORTH-
CENTRAL IDAHO AND WESTERN MONTANA LOWER VALLEYS.
AN UNSEASONABLY COLD AIRMASS WILL REMAIN ENTRENCHED ACROSS THE
NORTHERN ROCKIES THROUGH EARLY NEXT WEEK. COLD TEMPERATURES ALOFT
WILL MAINTAIN STEEP LAPSE RATES AND DAILY INSTABILITY SHOWERS.
ADDITIONALLY, HIGHER SURFACE PRESSURE EAST OF THE DIVIDE COUPLED
WITH LOWER PRESSURE TO OUR SOUTH AND WEST WILL DRIVE NOCTURNAL
EASTERLY WINDS. THIS EASTERLY FLOW AND ASSOCIATED OROGRAPHIC LIFT
WILL SUPPORT PERSISTENT SNOW SHOWERS ALONG AND WEST OF THE DIVIDE,
PARTICULARLY ACROSS THE GLACIER REGION.
FREEZE WARNINGS AND FROST ADVISORIES REMAIN IN EFFECT FOR MANY
LOWER VALLEYS. WHILE PATCHY CLOUD COVER AND CHANNELED EASTERLY
WINDS MAY LIMIT COOLING IN SOME LOCALIZED AREAS, OPTIMAL
RADIATIONAL COOLING ELSEWHERE WILL ALLOW TEMPERATURES TO PLUMMET
INTO THE TEENS AND LOW 20S. THIS POSES A CONTINUING THREAT TO
UNPROTECTED OUTDOOR PLUMBING AND IRRIGATION SYSTEMS.
MODEL GUIDANCE HIGHLIGHTS A SECONDARY UPPER-LEVEL TROUGH DROPPING
INTO IDAHO SUNDAY, FOCUSING PRECIPITATION ACROSS SOUTHERN IDAHO
AND LEMHI COUNTIES. THIS FEATURE BRINGS THE POTENTIAL FOR WINTER
DRIVING CONDITIONS AND SNOW-COVERED ROADS AT LOST TRAIL PASS AND
OTHER SOUTHWEST MONTANA PASSES BY MONDAY MORNING.
BROAD CYCLONIC FLOW PERSISTS THROUGH WEDNESDAY AS THE PRIMARY
UPPER LOW SHIFTS TOWARD THE GREAT LAKES. THIS PATTERN WILL
MAINTAIN BELOW-AVERAGE TEMPERATURES, FROSTY MORNINGS, AND DAILY
AFTERNOON INSTABILITY SHOWERS.
A SIGNIFICANT PATTERN SHIFT ARRIVES LATE IN THE WEEK AS A HIGHLY
AMPLIFIED UPPER RIDGE BUILDS INTO THE REGION. ENSEMBLE PROBABILITIES
STRONGLY HIGHLIGHT A RETURN TO THE 70S FOR WESTERN MONTANA
VALLEYS, WITH TEMPERATURES APPROACHING 80 DEGREES IN HELLS CANYON.
AVIATION
PATCHY FOG WILL BE POSSIBLE THIS MORNING FOR VALLEY
LOCATIONS THAT SEE CLEARING TOWARDS SUNRISE, MOSTLY NOTABLY FOR
KMSO AND KGPI. ANY FOG THAT DEVELOPS WILL BE SHORT LIVED. AN
UNSEASONABLY COLD AIRMASS WILL MAINTAIN STEEP LAPSE RATES ACROSS
THE NORTHERN ROCKIES, PROMOTING SCATTERED DIURNAL RAIN AND SNOW
SHOWERS THAT WILL YIELD LOCALIZED MVFR TO IFR CONDITIONS AND
WIDESPREAD MOUNTAIN OBSCURATIONS. THESE OROGRAPHIC SNOW SHOWERS
WILL BE MOST PERSISTENT ALONG AND WEST OF THE CONTINENTAL DIVIDE,
PARTICULARLY IMPACTING THE GLACIER REGION AIRSPACE. OVERNIGHT, A
TIGHTENING PRESSURE GRADIENT WILL DRIVE ENHANCED EASTERLY WINDS
THROUGH TERRAIN-CHANNELED VALLEYS, INTRODUCING THE POTENTIAL FOR
LOW-LEVEL MECHANICAL TURBULENCE AND LOCALIZED CROSSWINDS AT
IMPACTED TERMINALS. OTHERWISE, PREDOMINANTLY VFR CONDITIONS ARE
EXPECTED OUTSIDE OF SHOWER ACTIVITY AND PATCHY MORNING CLOUD
COVER.
MSO WATCHES/WARNINGS/ADVISORIES
MT...FREEZE WARNING UNTIL 8 AM MDT SUNDAY FOR BITTERROOT/SAPPHIRE
MOUNTAINS...FLATHEAD/MISSION VALLEYS...KOOTENAI/CABINET
REGION...LOWER CLARK FORK REGION...MISSOULA/BITTERROOT
VALLEYS.
ID...FREEZE WARNING UNTIL 8 AM MDT /7 AM PDT/ SUNDAY FOR EASTERN
LEMHI COUNTY...NORTHERN CLEARWATER MOUNTAINS...SOUTHERN
CLEARWATER MOUNTAINS.
FROST ADVISORY UNTIL 8 AM MDT /7 AM PDT/ SUNDAY FOR
OROFINO/GRANGEVILLE REGION...WESTERN LEMHI COUNTY.
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