051
FXUS65 KMSO 220910
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
310 AM MDT THU OCT 22 2026
DISCUSSION
KEY MESSAGES:
- MILD DAYTIME TEMPERATURES THROUGH TODAY.
- SIGNIFICANT WEATHER CHANGE COMING TONIGHT INTO FRIDAY.
TODAY WILL OFFER THE LAST DAY THIS WEEK OF MILD DAY-TIME
TEMPERATURES, WITH HIGHS RISING TO AROUND 10 DEGREES ABOVE NORMAL.
STABLE CONDITIONS THIS MORNING LED TO VALLEY FOG DEVELOPMENT,
WITH FOG EXPECTED TO BURN OFF FOR MOST AREAS BY 800-900 AM MDT.
WATER VAPOR IMAGERY THIS MORNING SHOWS A CLOSED LOW SPINNING OVER
CALIFORNIA. THIS LOW WILL BEGIN TO TRACK NORTHEASTWARD INTO THE
GREAT BASIN BY LATER THIS AFTERNOON. HIGH-RESOLUTION MODELS
SUGGEST MOISTURE AND INSTABILITY WILL QUICKLY MOVE SOUTH TO NORTH,
WITH SHOWERS AND ISOLATED THUNDERSTORMS DEVELOPING ACROSS CENTRAL
IDAHO AND SPREADING INTO LEMHI AND IDAHO COUNTIES IN IDAHO. THIS
ACTIVITY WILL TRACK INTO SOUTHWEST MONTANA BY EARLY EVENING, WITH
THE THREAT FOR THUNDERSTORMS DECREASING AS THE SUN BEGINS TO SET.
A SIGNIFICANT CHANGE ARRIVES TONIGHT INTO FRIDAY, AS A LOW
PRESSURE SYSTEM AND COLD FRONT TRACKS ACROSS THE REGION. THIS
SYSTEM WILL BRING COLDER TEMPERATURES AND WIDESPREAD PRECIPITATION.
PRECIPITATION AMOUNTS HAVE CONTINUED TO TREND HIGHER OVER THE
LAST 24 HOURS, AS MODEL GUIDANCE TRACKS A MID-LEVEL LOW ALONG THE
DIVIDE IN SOUTHWEST MONTANA BY FRIDAY MORNING. WIDESPREAD
PRECIPITATION WILL WRAP AROUND THE WEST-NORTHWEST AREA OF THIS LOW
WITH PROLONGED RAINFALL FOR MUCH OF FRIDAY ALONG AND SOUTH OF THE
INTERSTATE 90 CORRIDOR. RESIDENTS IN NORTH-CENTRAL IDAHO AND
NORTHWEST MONTANA WILL SEE THE MAJORITY OF RAIN AFTER MIDNIGHT
INTO MID-MORNING FRIDAY AS THE COLD FRONT PASSES. THE COLD AIR
WILL LAG BEHIND MOST OF THE PRECIPITATION, WITH MINOR SNOW AMOUNTS
FOCUSED ABOVE 6,000 FEET.
THE LOW WILL DEPART TO THE EAST FRIDAY NIGHT, WITH DRY CONDITIONS
RETURNING ACROSS THE REGION ON SATURDAY. FORECAST UNCERTAINTY
BEGINS TO INCREASE BY SUNDAY. MODEL ENSEMBLE CLUSTER ANALYSIS
CONTINUES TO DISPLAY A WIDE ARRAY OF OUTCOMES AS A CLOSED LOW
DROPS SOUTHWARD FROM THE GULF OF ALASKA. ROUGHLY 40 PERCENT OF
ENSEMBLE MEMBERS PUSH THE CLOSED LOW ACROSS THE NORTHERN ROCKIES
BY LATE SUNDAY OR MONDAY, WITH THE REMAINING MEMBERS SUGGESTING
THE LOW MAY STALL OR RETROGRADE TO THE WEST. OVERALL, THE FORECAST
LEANS ON THE NBM BLEND, WHICH SUGGESTS MOSTLY DRY CONDITIONS
SUNDAY INTO MONDAY, WITH SHOWER CHANCES RETURNING BY TUESDAY AND
WEDNESDAY WHEN THE MAJORITY OF ENSEMBLE MEMBERS PUSH THIS LOW
FURTHER EAST TOWARDS THE NORTHERN ROCKIES.
AVIATION
MOSTLY CLEAR SKIES AND STABLE CONDITIONS THIS MORNING
ARE PROMOTING THE DEVELOPMENT OF VALLEY FOG. BASED ON
OBSERVATIONAL TRENDS, KGPI WILL SEE THE GREATEST IMPACTS, WITH
PERIODS OF IFR TO LIFR VISIBILITY AND CEILINGS THROUGH AT LEAST
22/1500Z. SATELLITE AND SURFACE OBSERVATIONS FOR KMSO, SUGGEST FOG
DEVELOPMENT BETWEEN 22/1000-1200Z, WITH IMPACTS THROUGH
22/1400-1500Z. A LOW PRESSURE SYSTEM WILL MOVE NORTHWARD INTO THE
GREAT BASIN THIS AFTERNOON, SENDING ATMOSPHERIC MOISTURE AND
INSTABILITY NORTHWARD. THIS WILL SET THE STAGE FOR NUMEROUS
SHOWERS AND ISOLATED THUNDERSTORMS ACROSS NORTH-CENTRAL IDAHO AND
SOUTHWEST MONTANA BY MID-AFTERNOON THROUGH THE EVENING HOURS.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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