652
FXUS65 KMSO 181810
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
1210 PM MDT THU JUN 18 2026
DISCUSSION
KEY MESSAGES:
- A RIDGE BUILDING OVER THE REGION TODAY WILL CAUSE TEMPERATURES
TO WARM, FEW SHOWERS/STORMS AROUND GLACIER NP.
- A SURGE OF MONSOONAL MOISTURE FRIDAY NIGHT INTO SATURDAY MAY
BRING THUNDERSTORMS CAPABLE OF GUSTY WINDS AND BRIEF HEAVY RAIN
TO SOUTHWEST MONTANA AND LEMHI COUNTY.
THIS AFTERNOON THROUGH FRIDAY: WARMING TREND & GLACIER PARK
SHOWER POTENTIAL
AN UPPER-LEVEL RIDGE WILL BUILD ACROSS THE REGION THROUGH FRIDAY, DRIVING
DAYTIME TEMPERATURES INTO THE LOW TO MID-80S ACROSS WESTERN MONTANA VALLEYS
AND THE MID-90S FOR THE LOWER VALLEYS OF NORTH-CENTRAL IDAHO.
ACROSS NORTHWEST MONTANA, SCATTERED SHOWERS AND A 20% CHANCE OF
THUNDERSTORMS ARE EXPECTED THIS AFTERNOON, PRIMARILY CLUSTERED NEAR GLACIER
NATIONAL PARK. THE MAIN THREAT WITH ANY DEVELOPING CELLS WILL BE SUDDEN,
GUSTY OUTFLOW WINDS UP TO 35 MPH. ADDITIONALLY, A WEAK NORTHEASTERLY WIND
PUSH THIS EVENING MAY BRING GUSTS OF 20 TO 30 MPH FOR NORTHWEST
MONTANA EAST OF US-93 BUT MUCH WILL DEPEND ON THE COVERAGE OF
SHOWERS IN THE GLACIER REGION. BOATERS ON REGIONAL LAKES
(INCLUDING FLATHEAD LAKE) SHOULD REMAIN ALERT TO THESE SHIFTING,
GUSTY CONDITIONS.
FRIDAY NIGHT THROUGH SATURDAY: MONSOONAL MOISTURE PLUME & THUNDERSTORMS
MID-LEVEL MONSOONAL MOISTURE FROM THE GREAT BASIN WILL SHIFT NORTHWARD ON
FRIDAY. WHILE A FEW ISOLATED, HIGH-BASED SHOWERS MAY DEVELOP FRIDAY NIGHT,
LIMITED INSTABILITY SHOULD RESTRICT WIDESPREAD THUNDERSTORM ACTIVITY.
BY SATURDAY, CONDITIONS BECOME MUCH MORE FAVORABLE FOR SHOWERS AND
THUNDERSTORMS, CONCENTRATED PRIMARILY SOUTH OF A LINE FROM
RIGGINS, ID TO MACDONALD PASS, MT (TARGETING LEMHI COUNTY AND
SOUTHWEST MONTANA). THE STRONGEST STORMS MAY PRODUCE BRIEF HEAVY
DOWNPOURS AND GUSTY OUTFLOW WINDS UP TO 50 MPH. OUTDOOR
RECREATIONISTS SHOULD MONITOR THE SKY CLOSELY AND BE PREPARED TO
SEEK SHELTER IF STORMS APPROACH. CONSIDERABLE UNCERTAINTY REMAINS
REGARDING THE NORTHERN EXTENT OF THIS CONVECTION; WHILE SHOWERS
COULD EXPAND AS FAR NORTH AS MISSOULA, THE PROBABILITY REMAINS
BELOW 20%.
SUNDAY THROUGH NEXT WEEK: LINGERING DIVIDE SHOWERS THEN RIDGING
DAILY SHOWER AND THUNDERSTORM CHANCES WILL LINGER SUNDAY AND
MONDAY ACROSS NORTHWEST MONTANA, PARTICULARLY ALONG THE
CONTINENTAL DIVIDE, THOUGH OVERALL IMPACTS WILL BE MINIMAL AND
LOCALIZED.
STRONG UPPER-LEVEL RIDGING BUILDS BACK OVER THE NORTHERN ROCKIES BY
TUESDAY, USHERING IN A PROLONGED RETURN TO WARMER AND DRIER CONDITIONS
THROUGH LATE NEXT WEEK.
AVIATION
HIGH CONFIDENCE IN WIDESPREAD VFR CONDITIONS PREVAILING ACROSS ALL
WESTERN MONTANA AND NORTH-CENTRAL IDAHO TERMINALS THROUGH FRIDAY AS AN
UPPER-LEVEL RIDGE BUILDS OVER THE REGION. SCATTERED SHOWERS WILL DEVELOP
ACROSS THE GLACIER NATIONAL PARK REGION THIS AFTERNOON, BRINGING A 20%
PROBABILITY OF THUNDERSTORMS CAPABLE OF PRODUCING BRIEF, ERRATIC SURFACE
GUSTS UP TO 30 KT. ELSEWHERE, DIURNALLY DRIVEN WESTERLY WIND GUSTS OF 15 TO
20 KT WILL BE COMMON ACROSS MOST VALLEY TERMINALS THIS AFTERNOON BEFORE
QUICKLY DIMINISHING AROUND SUNSET. THIS EVENING INTO FRIDAY MORNING, A WEAK
LOW-LEVEL EASTERLY SURGE WILL TRACK ACROSS AREAS I-90 NORTHWARD, SHIFTING
SURFACE WINDS AND GENERATING GUSTS OF 15 TO 25 KT AT THE KGPI AND KMSO
TERMINALS. MID- TO HIGH-LEVEL CLOUD COVER WILL GRADUALLY OVERSPREAD THE
REGION FROM THE SOUTH ON FRIDAY, ACCOMPANIED BY A SLIGHT CHANCE OF ISOLATED
AFTERNOON THUNDERSTORMS DEVELOPING ACROSS SOUTHWEST MONTANA.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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