236
FXUS65 KMSO 290852
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
252 AM MDT MON JUN 29 2026
DISCUSSION
KEY MESSAGES:
- POTENTIAL FOR RAPIDLY RISING WATER LEVELS IN SMALL CREEKS AND
STREAMS ACROSS NORTHWEST MONTANA THIS AFTERNOON AND EVENING,
DUE TO HEAVY RAIN SHOWERS AND THUNDERSTORMS. LOCALIZED ROCKFALL
AND/OR DEBRIS FLOWS ARE POSSIBLE AS WELL.
- HYPOTHERMIA RISK CONTINUES THROUGH THE DAY MONDAY IN THE
BACKCOUNTRY.
- NEAR SEASONABLE TEMPERATURES ALONG WITH DAILY THUNDERSTORM
CHANCES ARE POSSIBLE TUESDAY THROUGH FRIDAY OF NEXT WEEK.
SATELLITE AND RADAR OBSERVATIONS SHOW A LARGE LOW PRESSURE SYSTEM
SPINNING OVER CENTRAL MONTANA, NEAR GREAT FALLS THIS MORNING, THAT
IS SPREADING MODERATE TO HEAVY RAINFALL ACROSS WESTERN MONTANA.
MODERATE SNOWFALL IS ALSO OCCURRING FOR ELEVATIONS ABOVE 6,500
FEET ACROSS THE NORTHERN ROCKIES. AS SUCH, WINTER STORM WARNINGS
REMAIN IN EFFECT THROUGH MID-MORNING. ALONG WITH IMPASSABLE
BACKCOUNTRY FOREST SERVICE ROADS, THE RISK FOR HYPOTHERMIA FOR
UNPREPARED RECREATIONISTS REMAINS DUE TO THE COLD AND WET
CONDITIONS.
RAINFALL TOTALS OVER THE PAST 36 HOURS ENDING THIS MORNING HAVE
RANGED BETWEEN 0.30 TO 1.50 INCHES ACROSS THE NORTHERN ROCKIES.
THE HIGHEST TOTALS HAVE FALLEN IN THE TERRAIN ALONG THE
CONTINENTAL DIVIDE FROM THE CANADIAN BORDER, SOUTH TO BUTTE.
SEVERAL INCHES OF SNOW HAVE ALSO BEEN REPORTED ACROSS THE REGION
WITH 6 INCHES AT LOST TRAIL PASS, 7 INCHES NEAR PORTERS CORNER IN
GRANITE COUNTY, MONTANA, AND 8 INCHES NEAR COBALT IN LEMHI COUNTY,
IDAHO.
WIDESPREAD MODERATE TO HEAVY RAIN AT TIMES WILL CONTINUE THROUGH
MID-MORNING TODAY. RAINFALL RATES THIS MORNING WILL GENERALLY
RANGE FROM 0.10 TO 0.20 INCHES PER HOUR. THESE RATES ARE EXPECTED
TO INCREASE LATER THIS AFTERNOON AND EVENING, WHEN HEAVY SHOWERS
AND THUNDERSTORMS DEVELOP BETWEEN 2 PM AND 10 PM. DURING THIS
TIME, RATES OF 0.50 INCHES PER HOUR OR MORE ARE EXPECTED UNDER
THE HEAVIER SHOWERS. THE LATEST FORECAST ENSEMBLE MODELS SHOW
ADDITIONAL RAINFALL TOTALS THROUGH TUESDAY MORNING RANGING BETWEEN
0.75 AND 1.50 INCHES ACROSS THE NORTHERN ROCKIES. THE HIGHER
TERRAIN ALONG THE CONTINENTAL DIVIDE AND THE MISSION RANGE HAS
ADDITIONAL EXPECTED AMOUNTS OF 1 TO 2 INCHES. SOME OF THESE TOTALS
ACCOUNT FOR THE POTENTIAL FOR HEAVY RAINFALL WITH SCATTERED
THUNDERSTORMS THIS AFTERNOON AND EVENING, SO NOT EVERYONE WILL SEE
THESE HIGHER AMOUNTS. THIS WILL BE ON TOP OF WHAT HAS ALREADY
FALLEN.
SMALL STREAMS AND CREEKS MAY EXPERIENCE RAPID RISES THIS EVENING
WITH THE EXPECTED ADDITIONAL RAIN, ALONG WITH THE THREAT FOR
ROCKFALL AND/OR DEBRIS FLOWS. THE HIGHEST RISK FOR THESE IMPACTS
IS MOST LIKELY TO OCCUR IN THE HIGHER TERRAIN ALONG THE DIVIDE AND
THE MISSION RANGE, NORTH OF MISSOULA. ADDITIONAL FLOOD WATCHES MAY
NEED TO BE ISSUED THIS MORNING TO ACCOUNT FOR THESE RISKS.
GIVEN THE WIDESPREAD PRECIPITATION, FOG AND LOW CLOUDS COULD CAUSE
TRAVEL ISSUES ACROSS THE REGION TUESDAY MORNING. THE LINGERING
MOISTURE WILL ALSO SUPPORT SCATTERED SHOWERS LATER IN THE DAY.
A MODERATING TREND IS EXPECTED LATER THIS WEEK WITH POSSIBLE
THUNDERSTORMS EACH DAY. WITH THE ADDED LOW-LEVEL MOISTURE FROM ALL
THE RAIN, THIS COULD ENHANCE INSTABILITY EACH DAY.
AVIATION
SATELLITE AND RADAR OBSERVATIONS SHOW A LARGE LOW
PRESSURE SYSTEM SPINNING OVER CENTRAL MONTANA, NEAR GREAT FALLS
THIS MORNING, THAT IS SPREADING MODERATE TO HEAVY RAINFALL ACROSS
WESTERN MONTANA. MODERATE SNOWFALL IS ALSO OCCURRING FOR
ELEVATIONS ABOVE 6,500 FEET ACROSS THE NORTHERN ROCKIES. THE
WIDESPREAD RAINFALL WILL PERIODICALLY REDUCE VISIBILITY AND
CEILING FOR ALL AVIATION SITES THROUGHOUT THE DAY, ALONG WITH
MOUNTAIN OBSCURATIONS. THIS AFTERNOON HEAVIER SHOWERS AND
SCATTERED THUNDERSTORMS ARE EXPECTED TO DEVELOP BETWEEN 29/2000Z
AND 30/0400Z THIS EVENING. THESE SHOWERS AND THUNDERSTORMS WILL BE
CAPABLE OF PRODUCING SHORT BURSTS OF 0.50" PER HOUR RAINFALL
RATES AS THEY PASS OVERHEAD. KGPI, KMSO, AND KHRF WILL HAVE THE
HIGHEST RISK FOR THESE HEAVIER SHOWERS. GIVEN THE RECENT
WIDESPREAD PRECIPITATION, FOG AND LOW CLOUDS COULD CAUSE TRAVEL
ISSUES ACROSS THE REGION TUESDAY MORNING. AFTERNOON SHOWERS WILL
REMAIN IN THE FORECAST, THROUGH THE WIDESPREAD PERSISTENT
PRECIPITATION WILL HAVE ENDED BY SUNRISE TUESDAY.
MSO WATCHES/WARNINGS/ADVISORIES
MT...WINTER STORM WARNING UNTIL 9 AM MDT THIS MORNING FOR
BITTERROOT/SAPPHIRE MOUNTAINS...BUTTE/BLACKFOOT REGION.
FLOOD WATCH UNTIL 3 AM MDT EARLY THIS MORNING FOR
FLATHEAD/MISSION VALLEYS...POTOMAC/SEELEY LAKE REGION...
WEST GLACIER REGION.
LAKE WIND ADVISORY UNTIL 3 AM MDT EARLY THIS MORNING FOR
FLATHEAD/MISSION VALLEYS.
ID...WINTER STORM WARNING UNTIL 9 AM MDT THIS MORNING FOR EASTERN
LEMHI COUNTY...WESTERN LEMHI COUNTY.
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