622
FXUS65 KMSO 171939
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
139 PM MDT FRI JUL 17 2026
DISCUSSION
KEY MESSAGES:
- STRONG TO SEVERE THUNDERSTORMS THIS AFTERNOON AND EVENING,
BRINGING THE THREAT OF STRONG WINDS, LARGE HAIL, AND HEAVY RAIN.
- TRENDING DRIER AND BREEZY THIS WEEKEND. ELEVATED FIRE WEATHER BY
SUNDAY FROM HOT, DRY, AND BREEZY CONDITIONS, ESPECIALLY IN
NORTHWEST MONTANA
- THUNDERSTORMS RETURN BY TUESDAY NEXT WEEK WITH THE NEXT MONSOON
MOISTURE SURGE.
MONSOONAL MOISTURE HAS PEAKED OVER THE REGION, WITH ATMOSPHERIC
MOISTURE CONTENT RUNNING AT 200 PERCENT OF NORMAL AND PRECIPITABLE
WATER VALUES OVER 1 INCH. IMPRESSIVE INSTABILITY ALONG WITH AN
INCOMING WAVE OF ENERGY CURRENTLY MOVING THROUGH CENTRAL IDAHO
SETS THE STAGE FOR WIDESPREAD THUNDERSTORM DEVELOPMENT THIS
AFTERNOON. HIGH RESOLUTION MODELS SHOW CONVECTION FORMING OVER THE
SOUTHERN BITTERROOT MOUNTAINS AROUND 2 TO 3PM, MOVING NORTHWARDS
AND POTENTIALLY FORMING INTO A LINE OF STORMS THAT COULD HOLD
TOGETHER INTO NORTHWEST MONTANA THIS EVENING. GUSTY WINDS WILL BE
THE MAIN CONCERN WITH THIS CONVECTION, WITH GUSTS 40 TO 50 MPH
ANTICIPATED WITH STRONGER STORMS. IT SHOULD BE NOTED THAT A FEW
OF OUR HIGH RESOLUTION MODELS ARE SHOWING THE POTENTIAL FOR GUSTS
OVER 60 MPH THROUGH THE MISSOULA VALLEY NORTHWARDS INTO THE
MISSION VALLEY EARLY THIS EVENING. WHILE NOT A LIKELY SCENARIO (10
TO 20 PERCENT CHANCE) IT IS SOMETHING THAT WILL BE MONITORED
CLOSELY MOVING FORWARDS. FURTHER NORTH, IN NORTHWEST MONTANA, HAIL
BECOMES MORE OF A CONCERN DUE TO INCREASED SHEAR VALUES. IT
SHOULD ALSO BE NOTED THAT THUNDERSTORMS COULD LINGER ACROSS
NORTHWEST MONTANA THROUGH EARLY SATURDAY MORNING.
STORMS WILL ALSO BE CAPABLE OF VERY HEAVY RAINFALL RATES OF 0.75"
OR MORE PER HOUR. FORTUNATELY STORM MOTION SHOULD KEEP CELLS
MOVING FAIRLY RAPIDLY WHICH OVERALL DECREASES THE FLASH FLOODING
RISK. HOWEVER, SENSITIVE FLOOD PRONE AREAS AND RECENT BURN SCARS,
PARTICULARLY IN LEMHI COUNTY AND SOUTHWEST MONTANA, COULD HAVE
FLOOD CONCERNS IF THEY TAKE A DIRECT HIT FROM THUNDERSTORMS.
ON SATURDAY, THE LOW PRESSURE SYSTEM THAT HAS BEEN SITTING OFF THE
PACIFIC NORTHWEST COAST SLOWLY MOVES THROUGH SOUTHERN BRITISH
COLUMBIA AND ALBERTA, FLATTENING THE RIDGE OF HIGH PRESSURE AND
BRINGING MORE WESTERLY FLOW ALOFT. THIS WILL SHIFT THUNDERSTORM
POTENTIAL PRIMARILY TO LOCATIONS SOUTH OF INTERSTATE 90. NEVER
THE LESS, A FEW STORMS STILL COULD BECOME STRONG IN THESE AREAS
WITH GUSTY WINDS, AND BRIEF HEAVY RAIN THE MAIN THREATS. FURTHER
NORTH ACROSS NORTHWEST MONTANA, BREEZY WESTERLY WINDS WILL
DEVELOP. THIS COUPLED WITH MUCH DRIER AIR COULD ENHANCE FIRE
WEATHER CONCERNS. BY SUNDAY, MUCH DRIER AIR MOVES OVER ALL OF
WESTERN MONTANA AND NORTH CENTRAL IDAHO, WITH HOT, DRY AND BREEZY
CONDITIONS ANTICIPATED.
GLOBAL ENSEMBLES SUGGEST THE NEXT SURGE OF MONSOON MOISTURE WILL
ARRIVE BY THE MIDDLE OF NEXT WEEK (TUESDAY INTO THURSDAY). CHANCES
FOR SHOWERS AND THUNDERSTORMS WILL TREND HIGHER EACH DAY AS
PRECIPITABLE WATER VALUES REACH OVER ONE INCH.
AVIATION
THE ATMOSPHERE OVER THE NORTHERN ROCKIES AIRSPACE IS
UNSTABLE AND THUNDERSTORMS HAVE BEGUN TO DEVELOP. ANY THUNDERSTORM
WILL BE CAPABLE OF GUSTY OUTFLOW WINDS 40 TO 50 MPH, BUT THIS
THREAT IS HIGHER PROBABILITY AT KMSO AND KHRF BETWEEN 17/2200 AND
18/0200Z. ADDITIONALLY, HAIL 0.25 TO 1.00" IS POSSIBLE AT ALL
TERMINALS ALONG WITH BRIEF BUT HEAVY RAINFALL DEGRADING
VISIBILITY 2-4 STATUTE MILES. THUNDERSTORM THREAT DECREASES AFTER
18/0300Z BUT SHOWERS AND EMBEDDED THUNDERSTORMS WILL REMAIN A
THREAT IN NORTHWEST MT OVERNIGHT.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...
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