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Area forecast discussion 
National Weather Service Glasgow Montana 
928 am MDT Sat Mar 20 2010 


Short term...for northeast Montana...today through Monday... 
no update to going forecast. Upper ridge building into the 
northern rockies...with clearing skies and warm air advection 
expected. Cold start to the morning will cap maximum temperatures 
but good mixing anticipated. Ebert 


Previous short term discussion...upper ridge currently over the 
Pacific coast will move inland today and across Montana tonight 
and Sunday. This will bring clear skies and a warming trend to the 
forecast area. While there will be a cooler NE to warmer SW 
temperature pattern today and Sunday...it will be due to warmer 
air over the SW. Snow cover has disappeared over most of the 
region this week so it is no longer much of a factor in cooling 
temperatures. 


Upper trough and cold front moves inland from the Pacific on 
Sunday. The cold front will pass through northeast Montana Monday 
morning followed by the upper trough in the afternoon and evening. 
Enough moisture...instability and upper level dynamics accompanies 
this system for a chance of showers. Temperatures will be warm 
enough on Monday for all rain. Forrester 


Long term...Monday night through Saturday... 
the polar vortex starts out over the Yukon territory and just to 
the west of the Hudson Bay. Pieces of shortwave energy rotate 
around the polar vortex and are ejected south southeastward towards 
the northern High Plains and Great Lakes region. The GFS European model (ecmwf) and 
the Gem are showing this pattern throughout the extended. As the 
short wave energy rounds the polar vortex it will pick up the 
Arctic air and trys to push it southward towards the lower 48. As 
it looks now the brunt of the Arctic air will remain north of the 
international border. This pattern could change with future model 
runs but the time of year and the dwindling snow pack across 
southern Canada is working against the really cold air making it 
to far south. 


So with this in mind the models show the Arctic frontal boundary 
wavering in and out of the northeast zones. Did not change tempertures 
very much at all in the extended but did tweak a few day time 
highs during the up coming week. Epically for next Friday as this 
looks like the best chance for a glancing blow of the Arctic air. 
Being this far out the precipitation is tough to call but a mix of 
rain and snow with mostly snow during the overnight hours is 
possible. Of course if the models change and send the blast of 
Arctic air through southern Montana...the precipitation type would 
be all snow. 


Models have been fairly consistent lately in showing a shortwave moving 
across western Montana on Monday night and Tuesday with enough 
instability and cold air working it way into the County Warning Area for snow 
showers Monday night and then a mix of rain and snow showers for 
Tuesday. This will come to an end as both models show an upper 
ridge building in from the west Tuesday night into Wednesday to 
put an end to the mixed precipitation through Thursday morning. By 
Thursday afternoon one of those earlier mentioned shortwaves 
rotating around the polar vortex and move southeast Ward across 
southern Canada. This will drop an Arctic front into the northeastern 
zones by Thursday evening. At the same time an upper low moves 
onshore and bring Pacific moisture to northern Montana. The upper 
low overruns the Arctic front which will produce precipitation. Again 
depending on how much of the Arctic air mass makes it into nemont 
will determine if we are dealing with all snow or a rain snow 
mix. Left the southern zones with a rain snow mix and the northern 
to northeast zones as all snow on Friday. Rsmith 


&& 


Aviation... 
expect VFR conditions to prevail the rest of today through tonight at 
all terminals. Scattered high cirrostratus clouds around 20 kft are 
likely. The winds will be southwest at 10 to 15 kts today and then 
back slightly to the south at under 10 kts overnight. Ghicks/rsmith 


&& 


Glasgow watches/warnings/advisories...none. 


&& 


$$ 


Weather.Gov/Glasgow