283  
FXUS65 KMSO 301013  
AFDMSO  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MISSOULA MT  
413 AM MDT THU MAR 30 2017  
   
DISCUSSION
 
AN UPPER LEVEL LOW PRESSURE SYSTEM MOVING ON SHORE  
OVER CENTRAL OREGON EARLY THIS MORNING WILL DIG SOUTH INTO NEVADA  
BY THIS AFTERNOON. AT THE SAME TIME A MID-LEVEL CIRCULATION WILL  
DEVELOP NORTH OF THE MAIN UPPER LOW, BRINGING WITH IT AN AREA OF  
HEAVIER PRECIPITATION. AND HERE IN LIES THE MAIN FORECAST  
CHALLENGE OVER THE NEXT 24 HOURS.  
 
FORECAST MODELS HAVE BEEN CONSISTENTLY INCONSISTENT, SO TO SPEAK,  
FOR SEVERAL DAYS NOW WITH EACH MODEL PRESENTING VARYING REALISTIC  
SOLUTIONS FOR WHERE THIS MID-LEVEL CIRCULATION WILL DEVELOP. THE  
GFS AND ECMWF ARE FARTHER NORTH AND SPREAD THE HEAVIEST  
PRECIPITATION OVER ALL OF LEMHI COUNTY, BUT AS FAR NORTH AS THE  
ANACONDA/BUTTE/SOUTHERN BITTERROOT AREAS OF SW/SC MONTANA. YET  
THE NAM AND CANADIAN SOLUTIONS MAINTAIN THEIR INSISTENCE THAT THIS  
PRECIPITATION WILL BARELY INFLUENCE LEMHI COUNTY AND SW/SC  
MONTANA, INSTEAD FALLING ACROSS SOUTHERN IDAHO (BOISE/POCATELLO  
AREAS). BASED ON THE LATEST SATELLITE, RADAR AND SURFACE PRESSURE  
TRENDS IN CENTRAL OREGON (WHERE THE MID LEVEL CIRCULATION IS  
BEGINNING TO TAKE SHAPE) WE'RE INCLINED TO BELIEVE A MORE  
NORTHERLY TRACK. THIS MAINTAINS THE PREVIOUS FORECAST WHICH HAS  
THE HEAVIEST RAIN/SNOW FALLING THROUGHOUT LEMHI COUNTY AND EXTENDING  
NORTH UP TO THE FAR SOUTHERN BITTERROOT VALLEY & SW MONTANA  
(INCLUDING BUTTE AND ANACONDA). THIS FALLS IN LINE MOST WITH THE  
ECMWF ANALYSIS AND CONTINUES TO SUPPORT THE PREVIOUSLY ISSUED  
WINTER WEATHER ADVISORY ABOVE 6500 FEET, IN EFFECT UNTIL EARLY  
FRIDAY MORNING.  
 
TONIGHT COOLER AIR WILL BE BROUGHT INTO THE NORTHERN ROCKIES VIA  
PERSISTENT EASTERLY FLOW ALOFT. AND STEADY DRYING THROUGHOUT THE  
ATMOSPHERE WILL GRADUALLY END SHOWERS BY FRIDAY MORNING AND THE  
SKY START TO CLEAR IN RESPONSE TO DEVELOPING HIGH PRESSURE.  
SEASONABLY COOL, FRIDAY AND AT LEAST SATURDAY MORNING WILL BE  
QUITE NICE THROUGHOUT THE NORTHERN ROCKIES. BUT THIS WILL BE SHORT  
LIVED AS YET ANOTHER WEATHER SYSTEM BEGINS TO SPREAD CLOUDS AND  
EVENTUALLY PRECIPITATION INTO THE REGION LATE SATURDAY AND  
SATURDAY NIGHT.  
 
NEXT WEEK A COLD FRONT WILL MOVE THROUGH THE REGION SUNDAY NIGHT  
AND MONDAY. SHOWERS, SOME SNOW SHOWER IN THE MOUNTAINS, AND GUSTY  
WINDS ARE THE ONLY EXPECTED IMPACTS FROM THIS SYSTEM. THERE MAY BE  
SOME MINOR TRAVEL INCONVENIENCES DUE TO RAPIDLY CHANGING  
CONDITIONS. THE WORST CONDITIONS WILL LIKELY BE IN SOUTHERN LEMHI  
COUNTY, IDAHO AS THE MAIN ENERGY WITH THIS SYSTEM IS FORECAST TO  
MOVE THROUGH THE SNAKE RIVER BASIN AND INTO CENTRAL WYOMING. THIS  
WILL CAUSE WRAP AROUND MOISTURE AND COOLER TEMPERATURES IN LEMHI  
COUNTY.  
 
TUESDAY AND WEDNESDAY A RIDGE BUILDS OVER THE REGION, CAUSING SOME  
VERY NICE MARCH WEATHER. HOWEVER THE RIDGE WILL BE SHORTLIVED AND  
WHEN IT BREAKS DOWN WILL LEAVE CENTRAL IDAHO WITH MOIST, UPSLOPE  
FLOW AND RAIN SHOWERS.  
 

 
   
AVIATION
 
SHOWERS ARE LIKELY TO BRING TEMPORARY VISIBILITY  
REDUCTIONS AND OCCASIONALLY LOWERED CEILINGS AT KMSO AND KGPI.  
HOWEVER HEAVIER, MORE PERSISTENT RAIN AND EVEN SNOW WILL IMPACT  
AIR FIELD OPERATIONS AND WEATHER CONDITIONS AT KBTM AND KSMN.  
GUSTY NORTHERLY WINDS (AT LEAST 20 KNOTS) ARE ANTICIPATE THIS  
EVENING AS THE PRECIPITATION COMES TO AN END AT THESE AIRFIELDS  
AND THOUGH THE REGION.  
 

 
   
MSO WATCHES/WARNINGS/ADVISORIES
 
 
MT...NONE.  
ID...WINTER WEATHER ADVISORY UNTIL 9 AM MDT FRIDAY ABOVE 6500 FEET  
FOR THE EASTERN LEMHI COUNTY...WESTERN LEMHI COUNTY.  
 

 
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab MT Page
The Nexlab ID Page Main Text Page