032
FXUS65 KMSO 130721
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
121 AM MDT SAT SEP 13 2025
DISCUSSION
KEY MESSAGES:
- PATCHY MORNING VALLEY FOG TODAY, FOLLOWED BY SCATTERED AFTERNOON
SHOWERS AND THUNDERSTORMS UNDER A NORTHWESTERLY FLOW
- SIGNIFICANT UNCERTAINTY PERSISTS FOR A WEATHER SYSTEM EARLY
NEXT WEEK, WITH MODEL GUIDANCE SHOWING A WIDE RANGE OF
POSSIBILITIES FROM VERY LITTLE RAIN TO WIDESPREAD, BENEFICIAL
PRECIPITATION.
EARLY MORNING SHOWERS/THUNDERSTORMS CONTINUE IN NORTHWEST MONTANA
BUT THEY WILL GRADUALLY DIMINISH AS THEY PUSH SOUTHWARD.
OTHERWISE, PATCHY VALLEY FOG COULD DEVELOP THIS MORNING IN
LOCATIONS THAT HAVE SEEN RECENT RAINFALL. HIGH PRESSURE WILL
ATTEMPT TO BUILD INTO THE REGION, BUT A PERSISTENT NORTHWESTERLY
FLOW ALOFT WILL KEEP THE PATTERN SOMEWHAT UNSETTLED TODAY. DURING
THE AFTERNOON, DAYTIME HEATING WILL COMBINE WITH THE COOL,
UNSTABLE NORTHWESTERLY FLOW TO TRIGGER SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS, MOSTLY ANCHORED TO THE TERRAIN.
BY SUNDAY, THE FLOW BECOMES MORE WESTERLY AND STABLE, WHICH
SHOULD RESULT IN A DRIER AND SUNNIER FIRST HALF OF THE DAY FOR
MOST. CLOUDS WILL BEGIN TO INCREASE SUNDAY AFTERNOON AS THE NEXT
WEATHER SYSTEM APPROACHES FROM THE PACIFIC. THIS SYSTEM IS
FORECAST TO MOVE INTO THE NORTHERN ROCKIES ON MONDAY, BRINGING A
RETURN TO COOLER AND WETTER CONDITIONS. HOWEVER, THERE IS
CONSIDERABLE UNCERTAINTY IN HOW THIS SYSTEM WILL EVOLVE AND,
CONSEQUENTLY, HOW MUCH RAIN WILL FALL AND WHERE.
ENSEMBLE MODEL CLUSTERS HAVE DIVERGED SIGNIFICANTLY AND ARE NOW
SPLIT NEARLY INTO THIRDS ON THE POTENTIAL OUTCOME:
- SCENARIO 1 (DRIEST): THE SYSTEM TRACKS IN A WAY THAT BRINGS
LIGHT RAIN, BUT MOSTLY DRY IN NORTHWEST MONTANA.
- SCENARIO 2 (MODERATE/TARGETED RAIN): THE SYSTEM DELIVERS MODEST
AND FOCUSED RAINFALL, PRIMARILY IMPACTING NORTH-CENTRAL IDAHO
AND WEST-CENTRAL MONTANA.
- SCENARIO 3 (WIDESPREAD RAIN): A MORE ORGANIZED AND SLOWER-
MOVING SYSTEM PROVIDES BENEFICIAL, WIDESPREAD RAINFALL ACROSS
MOST OF THE FORECAST AREA.
GIVEN THIS UNCERTAINTY, IT IS TOO EARLY TO PINPOINT SPECIFIC
IMPACTS, BUT RESIDENTS SHOULD BE PREPARED FOR THE POSSIBILITY OF A
COOL AND WET START TO THE WORK WEEK.
LOOKING FURTHER AHEAD, MODEL CLUSTERS SUPPORT BRIEF RIDGING THE MIDDLE
OF NEXT WEEK FOLLOWED BY ANOTHER TROUGH IMPACTING THE REGION TO
END NEXT WEEK, SUGGESTING THE ACTIVE, UNSETTLED PATTERN MAY
CONTINUE.
AVIATION
EARLY MORNING SHOWERS/THUNDERSTORMS CONTINUE IN
NORTHWEST MONTANA BUT THEY WILL GRADUALLY DIMINISH AS THEY PUSH
SOUTHWARD. OTHERWISE, AREAS OF PATCHY VALLEY FOG AND LOW STRATUS
CEILINGS ARE POSSIBLE, PARTICULARLY AT KGPI WHERE CONSIDERABLE
RAIN FELL LAST EVENING. WEAK RIDGING WILL HELP TO SUPPRESS
CONVECTION THIS AFTERNOON COMPARED TO RECENT DAYS. ALTHOUGH,
LINGERING MOISTURE AND DAYTIME HEATING WILL STILL ALLOW FOR
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS, MAINLY TERRAIN
ANCHORED, DIMINISHING AFTER SUNSET. VFR CONDITIONS ARE EXPECTED TO
PREVAIL FOR MOST OF THE TAF PERIOD OUTSIDE OF ANY SHOWER AND
STORM ACTIVITY.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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