983
FXUS65 KMSO 261815
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
1215 PM MDT SAT SEP 26 2026
DISCUSSION
KEY MESSAGES:
- MILD CONDITIONS THE REST OF THE WEEK WITH ONLY MINOR
DISTURBANCES.
- SHORTWAVE MONDAY TO BRING BREEZY CONDITIONS.
- POTENTIAL FOR A COLD FRONT FRIDAY INTO THE WEEKEND, BUT
CONFIDENCE IS LOW.
- CHANCES ARE INCREASING FOR A WARM, DRY EARLY OCTOBER BEYOND THE
7 DAY FORECAST.
OVERALL MILD CONDITIONS ARE EXPECTED THE REST OF THE WEEK. THE
WEATHER PATTERNS WE EXPECT THROUGHOUT THE WEEK ARE: WEAK ZONAL
(WEST-TO-EAST) FLOW ALOFT, A SHORTWAVE ON MONDAY IN SPLIT FLOW,
AND SOME WEAK RIDGING. THE SHORTWAVE ON MONDAY WILL CAUSE SOME
BREEZY CONDITIONS, BUT IT IS A RESULT OF A CUTOFF LOW SPLITTING
OUT OF THE FLOW AND DIVING INTO THE U.S. SOUTHWEST. AS A RESULT,
MOST OF THE ENERGY AND MOISTURE WILL GO TO THE SOUTH. DURING
PERIODS OF ZONAL FLOW, THERE WILL BE SOME MOISTURE MIXED IN, BUT
IT WILL ONLY AFFECT FAR NORTHWEST MONTANA AND GLACIER NATIONAL
PARK AROUND TUESDAY AND WEDNESDAY. EVEN FOR THAT THOUGH THERE'S
ONLY A 40% CHANCE OF UP TO 0.10 INCHES OF PRECIPITATION IN THE
MOUNTAINS.
SOME MODELS, NAMELY THE GFS, ARE GEARING UP FOR ANOTHER COLD FRONT
TO END THE WEEK ON FRIDAY INTO SATURDAY. LOOKING AT ENSEMBLE
CLUSTERS FOR RAIN, CURRENT FORECASTS ONLY SHOW AN 11% CHANCE OF
SOME MOISTURE WITH THAT EVENT AGAIN IN NORTHWEST MONTANA. MOST
ENSEMBLE MEMBERS DON'T SHOW A COLD FRONT AT ALL.
ACTIVE WEATHER IN THE TROPICS RIGHT NOW IS SETTING UP THE PATTERN
IN THE LONG TERM. WITH 3 HURRICANES IN THE CENTRAL AND EAST
PACIFIC OCEAN FROM HAWAII TO BAJA AND A TYPHOON APPROACHING THE
EASTERN PERIPHERY OF JAPAN, IT'S BEEN A DIFFICULT FORECAST FOR
MODELS. HOWEVER, THEY'RE STARTING TO COALESCE AROUND HIGHER
CHANCES FOR A POTENT RIDGE OVER THE NORTHERN ROCKIES INTO THE
FIRST THIRD OF OCTOBER. ENSEMBLE MEAN TEMPERATURE FORECASTS ARE
COMING IN 15 DEGREES ABOVE SEASONAL AVERAGES AT ABOUT 9-12 DAYS
OUT. THOSE ARE SOME LARGE ANOMALIES FOR THAT LONG OF A LEAD TIME!
ADD IN THAT THE SIGNAL IS COMING FROM MULTIPLE ENSEMBLE SYSTEMS
INCLUDING BOTH DYNAMICAL (PHYSICS BASED) AND AI MODELING SYSTEMS,
IT GIVES ABOVE NORMAL LEVELS OF CONFIDENCE FOR SUCH A LONG LEAD
TIME FORECAST. LOOKING BACK, THE LAST TIME THIS KIND OF WARM
RIDGE SET UP OVER THE NORTHWESTERN US IN EARLY OCTOBER WAS OCTOBER
9-11 AND 14, 1991. EUREKA, MONTANA HIT 86 DEGREES, GRANGEVILLE,
IDAHO 87 DEGREES, AND BUTTE 81 DEGREES! THE CENTER FOR CLIMATE
PREDICTION HAS ISSUED FORECASTS FOR THE NORTHERN ROCKIES REGION
WITH A 60-70% CHANCE OF ABOVE AVERAGE TEMPERATURES AND
PRECIPITATION FORECASTS ARE LEANING BELOW AVERAGE FOR THAT TIME
PERIOD AS WELL.
AVIATION
TODAY AN UPPER LEVEL LOW IS EXITING THE REGION WITH A
WEAK RIDGE BUILDING IN BEHIND IT. GENERALLY EXPECT MID-LEVEL
CEILINGS RISING THROUGHOUT THE DAY WITH SOME CLEARING OVERNIGHT.
WITH STABLE CONDITIONS EXPECTED GOING INTO THE EVENING, VALLEY FOG
IS LIKELY ACROSS THE REGION. HOWEVER, WITH DEW POINTS IN THE LOW
TO MID 30S IN THE VALLEYS AND IN THE UPPER 20S ON THE RIDGES, WE
DO NOT EXPECT THE VALLEY FOG TO BE WIDESPREAD ENOUGH TO IMPACT
REGIONAL TERMINALS.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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