276
FXUS65 KMSO 202045
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
145 PM MST THU FEB 20 2025
DISCUSSION
KEY MESSAGES:
- INCREASED SNOWMELT AND RUNOFF SATURDAY INTO MONDAY, BRINGING
THE RISK OF MINOR FLOODING OF LOW-LYING AND POOR DRAINAGE AREAS
AND TO SMALL STREAMS AND CREEKS FROM POTENTIAL ICE JAM
RELEASES.
- WIDESPREAD RAIN AND HIGH ELEVATION MOUNTAIN SNOW, SUNDAY INTO
MONDAY.
- AREAS OF FREEZING RAIN SATURDAY AND SUNDAY MORNING ACROSS
WESTERN MONTANA WITH COLD SUBSURFACE GROUND TEMPERATURES IN
PLACE.
AN OVERALL DRYING AND WARMING TREND IS EXPECTED INTO FRIDAY AS A
RIDGE OF HIGH PRESSURE SETTLES OVER THE REGION. BY SATURDAY, THE
DISTURBANCE WILL MOVE IN, TRIGGERING SCATTERED SHOWERS ACROSS THE
NORTHERN ROCKIES. SNOW LEVELS WILL BEGIN TO RISE, KEEPING SNOWFALL
CONFINED TO HIGHER ELEVATIONS, WHILE VALLEYS WILL LIKELY SEE A
WINTRY MIX.
FORECAST MODELS CONTINUE TO INDICATE A LONG DURATION (36-48
HOURS) ATMOSPHERIC RIVER EVENT SUNDAY INTO MONDAY, LEADING TO
WIDESPREAD PRECIPITATION AND RAISING SNOW LEVELS ABOVE 5,000 FEET.
CLEARWATER COUNTY AND AREAS NEAR THE MONTANA-IDAHO BORDER COULD
SEE SIGNIFICANT RAINFALL, WITH AN 80% CHANCE OF MORE THAN AN INCH
ACCUMULATING OVER 48 HOURS. AND IN FACT, SOME OF THE HIGHER
TERRAIN, PARTICULARLY IN NORTH CENTRAL IDAHO COULD SEE OVER 2
INCHES OF LIQUID PRECIPITATION.
IN ADDITION TO THE RAIN, TEMPERATURES IN MOST VALLEYS WILL REMAIN
ABOVE FREEZING FROM SATURDAY NIGHT THROUGH TUESDAY, WITH NORTH-
CENTRAL IDAHO VALLEYS HAVING A 70% CHANCE OF STAYING ABOVE 40F ON
SUNDAY NIGHT. THE COMBINATION OF WARM TEMPERATURES AND PERSISTENT
RAINFALL COULD LEAD TO RAPID MELTING OF LOW-ELEVATION SNOW,
INCREASING THE RISK OF PONDING IN POOR DRAINAGE AREAS, LOCALIZED
MINOR FLOODING, AND ICE BREAKUPS ON SMALL CREEKS AND STREAMS. TO
MITIGATE POTENTIAL IMPACTS, CONSIDER CLEARING SNOW FROM DRAINAGE
AREAS AHEAD OF TIME.
ANOTHER KEY CONCERN WITH THIS SYSTEM IS THE POTENTIAL FOR ICY
CONDITIONS AS RAIN FALLS ON COLD GROUND, ESPECIALLY IN THE
OVERNIGHT HOURS SATURDAY AND SUNDAY. SUBSURFACE TEMPERATURES IN
MANY WESTERN MONTANA VALLEYS ARE CURRENTLY 2 TO 5 DEGREES BELOW
FREEZING, MEANING THAT EVEN IF AIR TEMPERATURES RISE ABOVE
FREEZING, RAIN COULD STILL FREEZE ON CONTACT. THIS MAY LEAD TO
EXTREMELY SLICK CONDITIONS, PARTICULARLY ON SECONDARY ROADS WHERE
LINGERING SNOW COVER FROM RECENT STORMS REMAINS. TRAVELERS SHOULD
USE CAUTION, ESPECIALLY ON UNTREATED SURFACES.
LOOKING FURTHER AHEAD, ANOTHER DISTURBANCE IS EXPECTED BY
MIDWEEK, BRINGING ADDITIONAL PRECIPITATION. HOWEVER, UNCERTAINTY
REMAINS REGARDING HOW MUCH COOLING WILL ACCOMPANY THIS SYSTEM,
MEANING SNOW LEVELS COULD STAY RELATIVELY HIGH FOR THIS TIME OF
YEAR.
AVIATION
SATELLITE IMAGERY THIS AFTERNOON SHOWS BREAKS IN THE
CLOUD COVER, WHILE RADAR LOOPS INDICATE SHOWERS REMAIN SCATTERED
ACROSS THE REGION. HOWEVER, DRIER AIR IS ON TRACK TO MOVE IN THIS
EVENING, LEADING TO A CONTINUED DECREASE IN BOTH SHOWER ACTIVITY
AND CLOUD COVER. FORECAST SOUNDINGS SUGGEST THE POTENTIAL FOR
LOWER STRATUS OR FOG TO DEVELOP BY FRIDAY MORNING. A MIX OF LOW
CLOUDS AND FOG IS MOST LIKELY IN NORTHWEST MONTANA, WHILE FOG IS
FAVORED FROM NORTH-CENTRAL IDAHO THROUGH WEST-CENTRAL MONTANA INTO
FRIDAY MORNING.
MSO WATCHES/WARNINGS/ADVISORIES
MT...FLOOD WATCH FROM SATURDAY AFTERNOON THROUGH MONDAY AFTERNOON FOR
BITTERROOT/SAPPHIRE MOUNTAINS...BUTTE/BLACKFOOT REGION...
FLATHEAD/MISSION VALLEYS...KOOTENAI/CABINET REGION...LOWER
CLARK FORK REGION...MISSOULA/BITTERROOT VALLEYS...
POTOMAC/SEELEY LAKE REGION...WEST GLACIER REGION.
ID...FLOOD WATCH FROM SATURDAY AFTERNOON THROUGH MONDAY AFTERNOON FOR
LOWER HELLS CANYON/SALMON RIVER REGION...NORTHERN
CLEARWATER MOUNTAINS...OROFINO/GRANGEVILLE REGION...
SOUTHERN CLEARWATER MOUNTAINS.
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