354
FXUS65 KMSO 120858
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
258 AM MDT TUE MAY 12 2026
DISCUSSION
KEY MESSAGES:
- NEAR-RECORD HEAT TODAY: HIGHS IN THE 80S TO LOW 90S. RIVERS
REMAIN DANGEROUSLY COLD AND FAST.
- TWO DISTINCT WIND THREATS WEDNESDAY: 1. SEVERE THUNDERSTORM
OUTFLOWS (60+ MPH) WEDNESDAY AFTERNOON, PRIMARILY FROM DEER
LODGE TO BUTTE AND SOUTHWARD. 2. STRONG, GUSTY WINDS
ACCOMPANYING THE COLD FRONT DURING AFTERNOON AND EVENING,
INCLUDING A 25% CHANCE OF LOCALIZED MOUNTAIN WAVE GUSTS IN
BITTERROOT VALLEY. EXPECT DANGEROUS CONDITIONS FOR BOATERS ON
LAKES AND INCREASED RISK FOR FIRE DANGER IN SOUTHWEST MONTANA.
- PRECIPITATION SHIFTS NORTH: FORECAST MODELS HAVE DRASTICALLY
SHIFTED THE RAIN/SNOW FOCUS TO CLEARWATER COUNTY INTO NORTHWEST
MONTANA FOR LATER WEDNESDAY.
- DRASTIC TEMPERATURE CRASH AND HYPOTHERMIA RISK: SUMMER ENDS
WEDNESDAY NIGHT. EXPECT MOUNTAIN HIGHS TO CRASH INTO THE LOW 40S
ON THURSDAY, AND DOWN TO THE 30S THIS WEEKEND WITH ACCUMULATING
SNOW. HIGH LEVEL BACKCOUNTRY RECREATIONISTS MUST PREPARE FOR
WINTER CONDITIONS. FROST COULD BE IN THE CARDS BY SUNDAY
MORNING.
TODAY (TUESDAY): HIGH PRESSURE PROVIDES ONE LAST DAY OF NEAR-
RECORD HEAT, WITH WIDESPREAD 80S AND LOW 90S. THIS IS LEADING TO
CONTINUED SNOWMELT WHICH IS KEEPING RIVERS ICE-COLD. COLD WATER
SHOCK REMAINS A SEVERE HAZARD FOR ANYONE RECREATING ON THE WATER
TODAY. AS OF 2AM MDT, THE CLARK FORK RIVER ABOVE MISSOULA IS AT
6.06 FEET AND COULD REACH THE ACTION STAGE BY FRIDAY.
WEDNESDAY AND THURSDAY (THE BIG TRANSITION): THE WEATHER WILL
SHIFT ON WEDNESDAY AS A POTENT COLD FRONT SWEEPS THROUGH. THE
TIMING HAS SPED UP; MISSOULA AND KALISPELL WILL LIKELY HIT THEIR
HIGH TEMPERATURES EARLIER BEFORE TEMPERATURES FALL. THE FRONT
COULD BE INTO THE CAMAS PRAIRIE IDAHO BY MID-MORNING, INTO WEST-
CENTRAL MONTANA BY EARLY AFTERNOON, AND BUTTE BETWEEN 6 AND 9 PM
MDT.
THE DUAL WIND THREAT:
1) COLD FRONT: THE MAIN HAZARD WEDNESDAY IS WIND, NOT JUST
THUNDERSTORMS. WHILE SCATTERED STORMS ARE POSSIBLE FROM LEMHI
COUNTY TO SOUTHWEST MONTANA, THEN SHIFTING EAST TOWARD HELENA,
MASSIVE PRESSURE RISES BEHIND THE FRONT (UP TO 12 MB IN 6 HOURS)
WILL DRIVE WESTERLY WIND GUSTS OF 35 TO 45 MPH WITH ISOLATED
HIGHER GUSTS, PARTICULARLY ACROSS SOUTHWEST MONTANA BY THE EVENING
HOURS. IMPACTS FROM THE COLD FRONT INCLUDE DANGER FOR SMALL CRAFT
AND BOATERS ON FLATHEAD LAKE AND OTHER LAKES. THERE COULD BE A
SLIGHT RISK FOR BROKEN BRANCHES AND ISOLATED POWER OUTAGES WITH
THE GUSTY WINDS.
2) HIGH-BASED SHOWERS AND THUNDERSTORMS MAY FORM AS
EARLY AS NOON OVER LEMHI COUNTY THEN TRACK TO THE NORTHEAST AT
SPEEDS OF 30 TO 45 MPH. WITH THE EXTREMELY HOT AND DRY AIR MASS
DOWNSTREAM, THESE COULD PRODUCE SEVERE DOWNBURSTS. THE HIGHER RISK
FOR THESE WILL GENERALLY BE EAST OF A LINE FROM MACDONALD PASS TO
GEORGETOWN LAKE TO LEMHI COUNTY. IMPACTS: SEVERE CROSS-WINDS ON
NORTH-SOUTH HIGHWAYS LIKE INTERSTATES 90 AND 15. INCREASED FIRE
DANGER IS POSSIBLE ACROSS SOUTHWEST MONTANA.
THE RAIN/SNOW SHIFT:
THE LATEST MODEL GUIDANCE CONTINUES TO DRASTICALLY SHIFT THE FOCUS
OF PRECIPITATION TO THE NORTH LATER WEDNESDAY AND WEDNESDAY
NIGHT. WHILE PREVIOUS FORECASTS FAVORED SOUTHERN AREAS, THE
NORTHERN TWO- THIRDS OF THE REGION ARE NOW FAVORED FROM A FEW
HUNDREDTHS UP TO 0.30” IN VALLEYS, AND UP TO 0.75” OF
PRECIPITATION IN THE MOUNTAINS. BECAUSE THE COLD UPPER TROUGH WILL
TRACK OVER NORTHWEST MONTANA INTO CANADA, SNOW LEVELS WILL BE
DRIVEN DOWN TO AROUND 5500 FEET. WE COULD BE LOOKING AT SEVERAL
INCHES OF NEW SNOW IN THE HIGH COUNTRY BY THURSDAY
MORNING(NORTHWEST MONTANA). HIKERS AND CAMPERS BE WARNED: YOU MAY
ENCOUNTER SLUSHY SNOW IN THE UPPER FOREST SERVICE ROADS AND IT
WILL BE QUITE CHILLY WITH GUSTY WINDS AND TEMPERATURES IN THE 40S
ON THURSDAY. THIS COULD BE A HYPOTHERMIA RISK SCENARIO FOR THOSE
NOT PREPARED.
FRIDAY THROUGH THE WEEKEND (RETURN TO WINTER):
A DEEP, ANOMALOUS UPPER-LEVEL LOW FROM THE GULF OF ALASKA WILL
PARK OVER THE NORTHERN ROCKIES THIS WEEKEND. TEMPERATURES ALOFT
WILL BE BITTERLY COLD WHICH COULD DRIVE SNOW LEVELS DOWN TO 4,000
FEET. HIGH TEMPERATURES IN THE MOUNTAINS WILL SIT IN THE 30S,
WHILE THE VALLEYS WILL ONLY SEE THE 50S (10 TO 15 DEGREES BELOW
NORMAL). STEEP INSTABILITY FROM THE COLD AIR ALOFT WILL TRIGGER
WIDESPREAD SHOWERS ALL WEEKEND. IN THE VALLEYS, HEAVY GRAUPEL
SHOWERS ARE POSSIBLE.
BOTTOM LINE FOR THE WEEKEND: ANYONE HEADING INTO THE BACKCOUNTRY
MUST PACK FOR WINTER SURVIVAL. THE COMBINATION OF WET SNOW, GUSTY
WINDS, AND FREEZING TEMPERATURES CREATES A HIGH RISK FOR
HYPOTHERMIA FOR THOSE EXPECTING SPRING CONDITIONS. WITH SUCH A
COLD SYSTEM TO VISIT OUR REGION, LOW TEMPERATURES BY SUNDAY AND
MONDAY MORNING COULD BE AT OR BELOW FREEZING WHICH COULD POSE A
FROSTY THREAT TO SENSITIVE VEGETATION. LET’S HOPE THAT THERE WILL
BE PERSISTENT CLOUD COVER TO KEEP US FROM GETTING TOO COLD!
AVIATION... CLEAR SKIES AND UNSEASONABLE HEAT WILL CONTINUE TODAY
(TUESDAY) AS HIGH PRESSURE HOLDS ON FOR ONE LAST DAY. EXPECT
GENERALLY LIGHT LOCAL WINDS AT THE TERMINALS TODAY. A DRAMATIC
SHIFT IN THE WEATHER ARRIVES ON WEDNESDAY. A STRONG COLD FRONT
WILL CROSS THE AIRSPACE, BRINGING A SHARP WIND SHIFT, FALLING
TEMPERATURES, AND SHOWERS. THUNDERSTORM OUTFLOW WINDS TO 45 KNOTS
ARE POSSIBLE AT KSMN AND TO 50+ KNOTS AT KBTM BETWEEN 13/1800Z AND
14/0000Z(NOON TO 6 PM WEDNESDAY). SNOW IS POSSIBLE IN THE HIGHER
ELEVATIONS OF NORTHWEST MONTANA WEDNESDAY NIGHT WHICH WOULD
PRODUCE MOUNTAIN OBSCURATION, ESPECIALLY IN THE GLACIER REGION.
MSO WATCHES/WARNINGS/ADVISORIES
MT...FIRE WEATHER WATCH FROM WEDNESDAY AFTERNOON THROUGH WEDNESDAY
EVENING FOR DEERLODGE/WEST BEAVERHEAD...EAST BEAVERHEAD.
ID...NONE.
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