336 
fxus65 kmso 231018 
afdmso 


Area forecast discussion 
National Weather Service Missoula Montana 
318 am MST sun Nov 23 2008 


Discussion...moist unstable air at the lower levels is keeping 
isolated showers going over portions of western Montana this hour. 
The showers are mainly from Polson through St. Ignatius over to 
The Divide and from Superior to Lolo Pass through Philipsburg. 
Only a dusting has been observed on the Lolo camera from these 
showers...but do expect them to linger through daybreak. The ridge 
will move into north central Idaho this morning and should spread enough 
stable dry air into western Montana to shut off these showers. In 
north central Idaho...where clearing has already occurred...patchy 
valley fog has formed...mainly in central and northern valleys of 
the Clearwater Mountains. This fog should burn off as inversions 
are not strong enough to keep the fog in the valleys. 


The ridge will build over the intermountain region this afternoon 
and will remain the dominant weather feature through Tuesday. 
Temperatures and fog development will be the main forecast 
challenges this period. With plenty of dry air under the 
ridge...valleys will get very cold but how cold is the question as 
fog development is also a possibility. Going forecast has lows 
below seasonal averages with highs above average...but not as warm 
as they could be. Expect inversions to strengthen each night which 
will limit amount of heating from lack of mixing. Tuesday night 
the models are advertising the ridge shifting east as a Pacific 
system approaches the coast. NAM is the odd model out bringing 
precipitation to the Clearwater Mountains while remaining models 
keep this region dry. Going forecast leans with the dry forecast 
and have opted to keep that trend going. With increased moisture 
and better mixing...temperatures will moderate Tuesday night into 
Wednesday. 


The spread in the model solutions becomes fairly significant by middle week. 
Most models agree that a cutoff low will linger over the southwest 
United States by late in the week...but the detail in the northern 
rockies differs from model to model. Previous forecast already 
accounted for the uncertainty so made very few changes. There is 
the potential for a high pressure system sliding east of The 
Rockies which will push some cooler air over the Continental 
Divide on Thanksgiving and a second push will come on Friday. 
Cooled temperatures down a little for this possibility. 




&& 


Aviation...stratus deck will linger over much of western Montana 
early this morning before the ridge builds overhead and dissipates 
the clouds. Clear skies will be common across north central Idaho 
and western Montana the rest of today through Monday. Some valley 
fog...mainly along rivers and wet lands will develop late tonight 
through early Monday. Kgpi and kmso are the main airfields 
expected to be impacted. 




&& 


Mso watches/warnings/advisories... 
Montana...none. 
Idaho...none. 
&& 


$$ 


Short term/aviation...Mead 
long term....loeffelbein