031
FXUS65 KMSO 191742
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
1142 AM MDT FRI JUN 19 2026
DISCUSSION
KEY MESSAGES:
- THUNDERSTORMS RETURN TO LEMHI COUNTY, IDAHO, AND SOUTHWEST
MONTANA THIS WEEKEND, BRINGING LIGHTNING AND BRIEF, ERRATIC
WIND GUSTS.
- A MINOR COOLING TREND THROUGH MONDAY WILL BE FOLLOWED BY A
WARMING TREND THROUGH MID-WEEK.
A SURGE OF MONSOONAL MOISTURE CURRENTLY VISIBLE ON WATER VAPOR
SATELLITE IMAGERY OVER NORTHERN CALIFORNIA AND SOUTHERN OREGON
WILL FILTER INTO THE NORTHERN ROCKIES THIS EVENING. AS THIS
MOISTURE ADVANCES, MID- TO HIGH-LEVEL CLOUD COVER WILL GRADUALLY
OVERSPREAD THE REGION FROM THE SOUTH TONIGHT.
BY SATURDAY, THIS MOISTURE PLUME WILL INTERACT WITH A WEAK
SHORTWAVE TROUGH DROPPING OUT OF THE NORTHWEST. THIS INTERACTION
WILL PROVIDE ENOUGH LIFT AND INSTABILITY TO TRIGGER SCATTERED
THUNDERSTORMS, PRIMARILY FOCUSED ACROSS LEMHI COUNTY, IDAHO, AND
SOUTHWEST MONTANA. WHILE MOISTURE LEVELS ARE NOT EXCEPTIONAL, THEY
ARE SUFFICIENT TO FUEL STORMS CAPABLE OF PRODUCING CLOUD-TO-
GROUND LIGHTNING AND BRIEF, GUSTY OUTFLOW WINDS. OUTDOOR
RECREATIONISTS IN THESE AREAS SHOULD MONITOR THE SKY AND BE
PREPARED TO SEEK SHELTER. FOR SATURDAY'S THUNDERSTORM POTENTIAL,
CONFIDENCE IS HIGH THAT STORMS WILL INITIATE IN SOUTHWEST MONTANA
AND LEMHI COUNTY. HOWEVER, THERE IS MODERATE UNCERTAINTY
REGARDING THE NORTHERN EXTENT OF THIS CONVECTION. ROUGHLY 20% OF
ENSEMBLE MEMBERS SUGGEST THE SHORTWAVE COULD DIG SLIGHTLY FURTHER
WEST, WHICH WOULD PULL SCATTERED SHOWERS AS FAR NORTH AS THE
MISSOULA OR BITTERROOT VALLEYS.
THE PASSAGE OF THIS WEAK TROUGH WILL SLIGHTLY DEPRESS
TEMPERATURES ACROSS THE REGION THROUGH MONDAY, KEEPING DAYTIME
HIGHS COMFORTABLE AND CLOSE TO SEASONAL AVERAGES. HOWEVER, AS THE
SHORTWAVE EXITS, ENSEMBLE GUIDANCE IS IN STRONG AGREEMENT THAT A
PROMINENT UPPER-LEVEL RIDGE ALONG THE US WEST COAST WILL
STRENGTHEN AND EXPAND EASTWARD. THIS BUILDING RIDGE WILL KICK OFF
A WARMING AND DRYING TREND ACROSS CENTRAL IDAHO AND WESTERN
MONTANA STARTING TUESDAY. STRONG SUBSIDENCE UNDER THE HIGH
PRESSURE WILL LEAD TO CLEAR SKIES AND LIGHTER WINDS. HIGH
TEMPERATURES WILL CLIMB INTO THE UPPER 80S TO NEAR 90 DEGREES IN
WESTERN MONTANA VALLEYS BY WEDNESDAY, MARKING SOME OF THE HOTTEST
DAYS OF THE YEAR SO FAR. LOWER ELEVATION RIVER VALLEYS IN CENTRAL
IDAHO WILL LIKELY PUSH INTO THE MID-TO-UPPER 90S.
UNCERTAINTY EMERGES BY LATE NEXT WEEK, WHERE ABOUT 50% OF THE
ENSEMBLE MODEL CLUSTERS DEPICT A DEEPER TROUGH APPROACHING THE
PACIFIC NORTHWEST BY FRIDAY. IF THIS DEEPER TROUGH MATERIALIZES,
IT WOULD BRING BREEZIER CONDITIONS AND INCREASED SHOWER CHANCES TO
THE REGION SLIGHTLY EARLIER THAN CURRENTLY FORECAST.
AVIATION
AN EASTERLY PRESSURE GRADIENT WILL CONTINUE TO CAUSE EAST WINDS
ALONG THE DIVIDE AND FURTHER WEST TOWARD KGPI AND KMSO INTO
TONIGHT. MID- TO HIGH- LEVEL CLOUDS WILL GRADUALLY INCREASE FROM
THE SOUTH TONIGHT AS A PLUME OF MID-LEVEL MOISTURE MOVES INTO THE
REGION. THE PRIMARY AVIATION CONCERN OVER THE NEXT 24 HOURS WILL
BE SCATTERED THUNDERSTORM DEVELOPMENT ON SATURDAY, SPECIFICALLY
IMPACTING THE KSMN AND KBTM TERMINALS. CONVECTIVE ACTIVITY IN
THESE AREAS WILL INTRODUCE THE THREAT OF ERRATIC, GUSTY OUTFLOW
WINDS AND TEMPORARY MVFR VISIBILITY REDUCTIONS IN BRIEF HEAVY
RAIN. THE REST OF THE REGION WILL LIKELY REMAIN DRY WITH WEST
WINDS OF 15-25 KNOTS, HOWEVER, A FEW MODELS SUGGEST A SLIGHT
CHANCE FOR STORMS FURTHER NORTH TOWARD KHRF AND KMSO.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...
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