736
FXUS65 KMSO 300918
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
318 AM MDT SAT MAY 30 2026
DISCUSSION
KEY MESSAGES:
- SATURDAY THROUGH MONDAY: A SLOW MOVING WEATHER SYSTEM WILL BRING
PROLONGED, HEAVY RAINFALL, FOCUSED ALONG THE DIVIDE AND IN
GLACIER PARK REGION.
- SIGNIFICANT RIVER RISES FROM WIDESPREAD RAIN AND SNOW MELT,
LEADING TO THE POTENTIAL MINOR FLOODING.
- SNOW LEVELS FALL NEAR 6,500-7,500 FEET TONIGHT INTO SUNDAY
MORNING, BRINGING WET SNOW ACROSS THE HIGH BACKCOUNTRY.
A SLOW MOVING LOW PRESSURE SYSTEM WILL TRACK NORTHWARD ACROSS
WYOMING INTO CENTRAL MONTANA BY THIS AFTERNOON AND EVENING. HIGH-
RESOLUTION MODEL GUIDANCE SUGGESTS WIDESPREAD RAIN WILL DEVELOP BY
LATE MORNING TO EARLY AFTERNOON ALONG THE DIVIDE IN SOUTHWEST
MONTANA, WITH RAIN SPREADING ACROSS WESTERN MONTANA THROUGH THE
EVENING TO OVERNIGHT HOURS. THIS LOW WILL TAP INTO ABNORMALLY HIGH
MOISTURE, WITH PWAT VALUES RUNNING 200% OF NORMAL ALONG THE
DIVIDE. A WEST-NORTHWEST FLOW WILL STRENGTHEN OVERNIGHT INTO
SUNDAY, FAVORING HIGHER PRECIPITATION TOTALS ACROSS THE GLACIER
PARK REGION, THE MISSION AND SWAN MOUNTAINS AND THE CONTINENTAL
DIVIDE IN SOUTHWEST MONTANA, WITH 1 TO 3 INCHES OF PRECIPITATION
ARE EXPECTED. THE HIGHEST AMOUNTS WILL FOCUS ACROSS THE GLACIER
PARK REGION, WHERE LOCALIZED AMOUNTS UP TO 4 INCHES CAN'T BE RULED
OUT THROUGH MONDAY MORNING. THE HIGHEST VALLEY RAIN TOTALS WILL
CENTER ALONG EASTERN PORTIONS OF THE FLATHEAD AND MISSION
VALLEYS, WHERE 1.00-2.00 INCHES ARE EXPECTED. CONFIDENCE IN
VALLEY RAIN TOTALS BEGINS TO DECREASE ALONG AND WEST OF THE US-93
CORRIDOR. RECENT MODEL TRENDS HAVE SHIFTED THE UPPER LEVEL LOW
FURTHER EAST, SUGGESTING LOWER CONFIDENCE FOR HIGHER RAIN TOTALS
ACROSS THESE LOCATIONS.
GIVEN RECENT RAINFALL FROM SHOWERS AND THUNDERSTORMS THE LAST
SEVERAL DAYS, MANY AREAS ARE EXPERIENCING SATURATED SOILS. GIVEN
THE SOIL CONDITIONS, AND WIDESPREAD RAIN COMBINED WITH ONGOING
HIGH-ELEVATION SNOWMELT, CONFIDENCE IS INCREASING FOR SHARP RISES
ON AREA WATERWAYS. THE CLARK FORK RIVER ABOVE MISSOULA, THE
FLATHEAD RIVER AT COLUMBIA FALLS, AND SWAN RIVER NEAR BIG FORK
ARE CURRENTLY FORECAST TO REACH MINOR FLOOD STAGE LATE SUNDAY OR
EARLY MONDAY. MINOR FLOODING AND WATER PONDING ON ROADS ARE ALSO A
CONCERN FOR LOW-LYING AND URBAN AREAS, PARTICULARLY WITHIN
FLATHEAD AND LAKE COUNTIES. RESIDENTS IN FLOOD-PRONE LOCATIONS
SHOULD CLEAR STORM DRAINS AND GUTTERS AHEAD OF TIME. IN ADDITION
TO WATER IMPACTS, STEEP CANYON TERRAIN WILL FACE AN ELEVATED RISK
OF ROCKFALLS AND MUDSLIDES. MEANWHILE, SHARP COOLING ALOFT WILL
CAUSE SNOW LEVELS TO DROP TO 6,000 TO 7,000 FEET ALONG THE
CONTINENTAL DIVIDE BY SUNDAY MORNING, BRINGING RAW, WINTER-LIKE
CONDITIONS AND HAZARDOUS TRAVEL TO BACKCOUNTRY USERS.
ONCE THE STORM SYSTEM EXITS, WEATHER MODELS FAVOR A BRIEF TRANSITION
BACK TO A HIGH-PRESSURE RIDGE BY THE MIDDLE OF THE WEEK. BY
THURSDAY AND FRIDAY NEXT WEEK, FORECAST CONFIDENCE BEGINS TO
DECREASE WITH ENSEMBLE MODEL GUIDANCE SUGGESTING THE POTENTIAL FOR
ANOTHER ROUND OF PACIFIC SYSTEMS AND WIDESPREAD RAIN, WHILE OTHER
SOLUTIONS SUGGEST WARM AND DRIER CONDITIONS.
AVIATION
A LOW PRESSURE SYSTEM WILL MOVE NORTHWARD INTO CENTRAL
MONTANA BY THIS AFTERNOON, WITH WIDESPREAD RAIN DEVELOPING ALONG
THE DIVIDE BY 30/1700-1900Z. WIDESPREAD TERRAIN OBSCURATIONS WILL
DEVELOP AS RAIN MOVES IN, WITH CEILINGS FALLING NEAR 2,500-3,000
FEET FOR KBTM. RAIN WILL SPREAD WEST-NORTHWEST THROUGH THE EVENING
COVERING MUCH OF WESTERN MONTANA. A NORTH-NORTHWEST GRADIENT WILL
REMAIN IN PLACE THROUGH THE AFTERNOON, WITH VALLEY TERMINALS
SEEING GUSTS OF 15-20KTS.
PATCHY VALLEY FOG HAS DEVELOPED IN THE VICINITY OF KGPI, WITH
VISIBILITY FLUCTUATIONS BETWEEN P6SM TO 2SM EXPECTED THROUGH
30/1200-1400Z. THEREAFTER, WINDS WILL BEGIN TO INCREASE WITH FOG
DIMINISHING.
MSO WATCHES/WARNINGS/ADVISORIES
MT...FLOOD WATCH FROM THIS EVENING THROUGH MONDAY MORNING FOR
FLATHEAD/MISSION VALLEYS...WEST GLACIER REGION.
ID...NONE.
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