838
FXUS65 KMSO 221809
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
1209 PM MDT FRI MAY 22 2026
DISCUSSION
KEY MESSAGES:
- WARMING AND DRYING TREND EXPECTED THROUGH THE WEEKEND.
- SHOWERS AND THUNDERSTORMS ON MEMORIAL DAY (MONDAY). ANY
LIGHTNING, SUDDEN WIND, OR RAPID TEMPERATURE DROP COULD BE
IMPACTFUL TO OUTDOOR RECREATIONALISTS. COLD FRONT MOVES THROUGH
BY TUESDAY MORNING.
- TUESDAY COULD BE QUITE THE WET DAY AS A LARGE UPPER LOW BECOMES
SITUATED TO OUR SOUTHWEST. THERE'S A 50 TO 70% PROBABILITY FOR
WIDESPREAD RAINFALL AMOUNTS EXCEEDING 0.25" BY WEDNESDAY
MORNING.
- UPPER LOW KEEPS UNSETTLED WEATHER GOING NEXT WEEK, SO KEEP THAT
RAIN GEAR HANDY!
THIS AFTERNOON:
SCATTERED SHOWERS ARE EXPECTED INTO THIS EVENING ACROSS NORTHWEST
MONTANA AND ALONG THE CONTINENTAL DIVIDE. IMPACTS WILL BE LIMITED
TO BRIEF, LOCALIZED RAINFALL AND GUSTY WINDS UP TO 30 MPH.
HOWEVER, MARGINAL INSTABILITY MAY BE SUFFICIENT TO TRIGGER AN
ISOLATED THUNDERSTORM, PRIMARILY WITHIN GLACIER NATIONAL PARK.
THIS WEEKEND/WATER SAFETY:
A SIGNIFICANT WARMING TREND WILL BRING SUMMER-LIKE TEMPERATURES
TO THE REGION FOR THE HOLIDAY WEEKEND. THESE WARM CONDITIONS WILL
LIKELY INCREASE OUTDOOR RECREATION ON AND AROUND AREA LAKES AND
RIVERS. HOWEVER, LOCAL WATERWAYS CONTINUE TO RUN DANGEROUSLY COLD
DUE TO ONGOING MOUNTAIN SNOWMELT. PLUNGING INTO COLD WATER WITHOUT
ACCLIMATIZATION CAN INDUCE COLD-WATER SHOCK DRASTICALLY ALTERING
BREATHING, HEART RATE, AND BLOOD PRESSURE, CREATING LIFE-
THREATENING CONDITIONS. ALWAYS WEAR A LIFE JACKET AND EXERCISE
EXTREME CAUTION. FOR MORE INFORMATION ON COLD-WATER HAZARDS, VISIT
WEATHER.GOV/SAFETY/COLDWATER.
MONDAY (MEMORIAL DAY):
ENSEMBLE GUIDANCE HAS CONVERGED SIGNIFICANTLY REGARDING MONDAY'S
WEATHER PATTERN. A LARGE UPPER-LEVEL LOW IS FORECAST TO DROP SOUTH
AND EAST INTO THE PACIFIC NORTHWEST BY MONDAY. THIS SETUP PLACES
THE REGION UNDER SOUTH-TO-SOUTHWEST FLOW ALOFT, A PATTERN
HISTORICALLY FAVORABLE FOR SHOWER AND THUNDERSTORM DEVELOPMENT.
WHILE INSTABILITY APPEARS MARGINAL, IT WILL BE SUFFICIENT TO
SUPPORT LIGHTNING, SMALL HAIL, AND GUSTY OUTFLOW WINDS. AS THE
FLOW SHIFTS MORE SOUTHERLY LATER MONDAY, INCREASING CLOUD COVER
WILL LIKELY LIMIT GREATER DIURNAL INSTABILITY. BOATERS AND
PADDLERS ON AREA LAKES SHOULD REMAIN ALERT FOR SUDDEN WIND SHIFTS
AND CHOPPY WATERS.
MONDAY NIGHT THROUGH TUESDAY NIGHT:
BY MONDAY NIGHT, WRAP-AROUND MOISTURE WILL OVERSPREAD THE REGION
AS A COLD FRONT MOVES INTO WESTERN MONTANA. ENSEMBLE CLUSTERS
STRONGLY AGREE ON BROAD, LARGE-SCALE ASCENT THROUGH TUESDAY NIGHT
AS THE UPPER-LEVEL LOW MEANDERS ACROSS OREGON, IDAHO, AND NEVADA.
CONSEQUENTLY, THE NATIONAL BLEND OF MODELS (NBM) HIGHLIGHTS THIS
TIMEFRAME FOR THE HIGHEST PROBABILITIES OF WIDESPREAD RAINFALL,
SHOWING A 50 TO 70 PERCENT CHANCE OF EXCEEDING 0.25 INCHES DURING
THE 48-HOUR PERIOD ENDING WEDNESDAY MORNING. WITH EXTENSIVE CLOUD
COVER AND PRECIPITATION, TUESDAY WILL LIKELY BE THE COOLEST DAY OF
THE WEEK, WITH HIGHS IN THE 50S AND 60S (5 TO 10 DEGREES BELOW
SEASONAL AVERAGES).
WEDNESDAY THROUGH FRIDAY:
AS THE CUTOFF LOW STALLS TO OUR SOUTH AND WEST, A PLUME OF GULF
MOISTURE IS PROJECTED TO ADVECT NORTHWARD ACROSS THE PLAINS AND
INTO WESTERN MONTANA BY WEDNESDAY AND THURSDAY. ENSEMBLES
HIGHLIGHT PRECIPITABLE WATER (PWAT) VALUES OF +2 TO +3 STANDARD
DEVIATIONS, OR OVER 150 PERCENT OF NORMAL. THIS UNUSUALLY MOIST
AIRMASS WILL HEIGHTEN THE RISK FOR HEAVY RAIN-PRODUCING SHOWERS
AND THUNDERSTORMS.
BY THURSDAY, ENSEMBLE CLUSTERS DEPICT A SLOW EASTWARD
PROGRESSION, POSITIONING THE CENTER OF THE LOW OVER NORTHERN
NEVADA. THE ENSEMBLE MEANS SHOW THE SYSTEM ACCELERATING SLIGHTLY
BY FRIDAY; HOWEVER, MODEL DISCREPANCIES REMAIN, WITH THE ECMWF
EJECTING THE LOW TOWARD THE YELLOWSTONE REGION WHILE THE GFS
ENSEMBLE MAINTAINS A MORE SOUTHERLY TRACK. WHILE A BELOW-NORMAL
MOUNTAIN SNOWPACK MEANS MAINSTEM RIVERS HAVE AMPLE CAPACITY TO
HANDLE THIS RAINFALL, SMALLER CREEKS AND STREAMS COULD BE HIGHLY
SENSITIVE TO LOCALIZED HEAVY DOWNPOURS. THIS HYDROLOGIC THREAT
WILL BE CLOSELY MONITORED IN UPCOMING FORECAST CYCLES.
AVIATION
SCATTERED SHOWERS ARE EXPECTED THIS AFTERNOON INTO EARLY
EVENING ACROSS NORTHWEST MONTANA AND ALONG THE CONTINENTAL
DIVIDE. SUFFICIENT INSTABILITY MAY SUPPORT AN ISOLATED
THUNDERSTORM NEAR GLACIER NATIONAL PARK. LOCALIZED WIND GUSTS OF
20-25 KNOTS WILL BE POSSIBLE NEAR ANY STRONGER SHOWER OR
THUNDERSTORM ACTIVITY, WITH POTENTIAL IMPACTS AT KGPI. OTHERWISE,
LIGHT AND DIURNALLY DRIVEN WINDS WILL PREVAIL AT ALL TERMINAL
SITES. VFR CONDITIONS ARE FORECAST TO PERSIST THROUGH SATURDAY AS
A WARMING AND DRYING TREND ESTABLISHES ACROSS THE REGION. WESTERLY
WINDS DO INCREASE ON SATURDAY AFTERNOON WITH GUSTS OF 15-25 KTS.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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