377  
FXUS65 KMSO 202030  
AFDMSO  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MISSOULA MT  
230 PM MDT MON MAY 20 2024  
   
DISCUSSION
 
MUCH LIKE YESTERDAY, SATELLITE AND RADAR LOOPS SHOW  
SHOWERS AND ISOLATED THUNDERSTORMS DEVELOPING THIS AFTERNOON IN  
AN UNSTABLE ENVIRONMENT AIDED BY DAYTIME HEATING. AFTER PEAK  
HEATING, RADAR PROJECTIONS INDICATE SHOWERS WILL DECREASE IN  
COVERAGE THIS EVENING. MOISTURE PROFILES SHOW A RETURN OF CLOUD  
COVER FOR TUESDAY MORNING, ESPECIALLY IN WESTERN MONTANA. HIGH-  
RESOLUTION MODELS PREDICT ANOTHER ROUND OF SHOWERS TUESDAY  
AFTERNOON, BUT WITH LESS OVERALL COVERAGE THAN TODAY.  
 
THE FOCUS REMAINS ON THE LOW-PRESSURE SYSTEM EXPECTED TO IMPACT  
THE REGION ON WEDNESDAY AND THURSDAY. MODELS SHOW STRONG AGREEMENT  
THAT THE LOW WILL SPREAD RAIN THROUGHOUT NORTH-CENTRAL IDAHO AND  
NORTHWEST MONTANA STARTING EARLY WEDNESDAY. BY WEDNESDAY  
AFTERNOON, WIDESPREAD RAIN IS EXPECTED TO REACH WESTERN MONTANA AS  
THE LOW-PRESSURE CENTER MOVES IN.  
 
AS THE LOW-PRESSURE CENTER PASSES THROUGH THE REGION WEDNESDAY  
NIGHT AND THURSDAY, SNOW LEVELS ARE FORECAST TO DROP. CONFIDENCE  
IS HIGH FOR SNOW ACCUMULATIONS ABOVE 6,000 FEET BY MIDDAY  
THURSDAY, LIKELY IMPACTING TRAVEL OVER PASSES SUCH AS LOST TRAIL,  
HOMESTAKE, AND MACDONALD. SOME MODELS SUGGEST SNOW LEVELS COULD  
FALL TO VALLEY FLOORS, BUT CONFIDENCE IN SNOW BELOW 5,000 FEET IS  
LOW. IF SNOW DOES REACH LOWER ELEVATIONS, IT COULD DAMAGE TREES  
AND CAUSE POWER OUTAGES DUE TO SAGGING VEGETATION OR BROKEN LIMBS.  
 
A WEAK RIDGE WILL BUILD OVER THE REGION ON FRIDAY, BRINGING A  
SLIGHT WARMING AND DRYING TREND. HOWEVER, THIS RIDGE WILL BE  
SHORT-LIVED AS ALL MODEL CLUSTERS INDICATE ANOTHER LOW-PRESSURE  
SYSTEM WILL IMPACT THE NORTHERN ROCKIES ON SATURDAY. FOLLOWING  
THIS SYSTEM, MODELS SUGGEST A RIDGE OF HIGH PRESSURE WILL BUILD  
OVER THE REGION BY EARLY NEXT WEEK.  
 

 
   
AVIATION
 
RADAR PROJECTIONS INDICATE THAT SHOWERS AND  
THUNDERSTORMS WILL CONTINUE TO AFFECT NORTH-CENTRAL IDAHO AND  
WESTERN MONTANA UNTIL AROUND SUNSET. AFTER SOME CLEARING THIS  
EVENING, MODEL CROSS-SECTIONS AND SOUNDINGS SUGGEST THAT CLOUD  
COVER WILL RETURN FOR TUESDAY MORNING. HIGH-RESOLUTION MODELS  
PREDICT ANOTHER ROUND OF SHOWERS TUESDAY AFTERNOON, BUT WITH LESS  
COVERAGE THAN TODAY.  
 

 
   
MSO WATCHES/WARNINGS/ADVISORIES
 
 
MT...WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH THURSDAY  
MORNING FOR BITTERROOT/SAPPHIRE MOUNTAINS...BUTTE/BLACKFOOT  
REGION.  
 
ID...WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH THURSDAY  
MORNING FOR EASTERN LEMHI COUNTY...WESTERN LEMHI COUNTY.  
 

 
 

 
 
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