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fxus65 ktfx 212350 
afdtfx 


Area forecast discussion 
National Weather Service Great Falls Montana 
500 PM MST Sat Nov 21 2009 


Updated aviation section 


Discussion... 


The upper level trough that moved through he region earlier today 
will exit it the region tonight followed by a brief period of 
drying under weak upper level ridging. Widely scattered snow 
showers over the mountains will diminish early this evening with a few 
isolated snow showers possible through early this evening as well 
along the Canadian border in association with a weak disturbance 
moving southeast from Alberta. Clouds and moisture will increase 
again on Sunday as a vigorous Pacific storm system moves onshore 
and quickly moves to the northern rockies by Sunday evening and 
across the state Sunday night. This system will bring another 
period of snow to the mountains Sunday afternoon and evening with 
snow showers possible elsewhere. Moist and unstable west to 
northwest flow will maintain at least a chance of snow showers over 
the central and SW Montana Mountains through Sunday night. Accumulations of an 
inch or less are expected across the valleys of SW Montana with 1 to 3 
inches possible in the mountains the most persistent snow will occur 
over the Gallatin and Madison Mountain ranges where higher amounts of 3 
to 5 inches appear likely for elevations above 6000 feet through 
Sunday night. Upper level ridging builds in behind this system on 
Monday for drier conditions. Temperatures will remain seasonably 
cool through Monday with clearing skies tonight allowing temperatures to 
drop into the single digits or lower in some of the SW Montana valleys. 
Hoenisch 


Monday night through Saturday night...the medium range models are in 
decent agreement into the middle of next week. Both models bring a 
weak shortwave trough over an upper level high pressure ridge parked 
along the Pacific coast through the area Monday night into 
Tuesday...which will bring a chance of precipitation to the area. 
This shortwave will also bring strong and gusty westerly downslope 
winds to the area...which will limit precipitation over the plains 
and warm temperatures to about 5 to 10 degrees above seasonal 
averages. Both models then amplify and shift the upper ridge into 
Montana Tuesday night into Thursday. This ridge will keep the area 
warm (temperatures 10 to 15 degrees above normal) and mostly dry. 
Gusty westerly surface winds will increase again Wednesday night 
into Thursday (thanksgiving day) as the next system approaches the 
area. The models begin to differ on Thursday. Unlike the model runs 
from last night...the European model (ecmwf) brings the next Pacific system through 
the state quicker than the GFS. With this uncertainty...have kept 
near climatological chances of precipitation over the tfx County Warning Area Friday 
through Saturday...with temperatures cooling to near seasonal 
normals by Saturday. An upper level ridge then begins to move into 
the western United States Saturday night...which should cause the 
chance for precipitation to decrease. Upper level support for the 
increasing winds through this period is temporary. Therefore...am 
not anticipating high wind highlights at this time and will not 
mention in the hazardous weather outlook. However...the potential 
for brief periods of strong winds still remains...and the situation 
will continue to be monitored. Coulston 
&& 


Aviation... 
updated 0000z. 
A weak upper level ridge will build over the region this 
evening...allowing for generally clear/partly cloudy skies over the 
region. The next Pacific storm will move into the Rocky Mountain 
front and southwest Montana after 17z Sunday...and then continue to 
affect the region through Sunday evening. VFR conditions are 
expected on Sunday morning...however...they will gradually lower to 
IFR/LIFR conditions over the region during the early afternoon hours 
on Sunday. Expect mountains to be obscured after 16z Sunday. Brusda 


&& 


Preliminary point temps/pops... 
gtf 24 38 29 42 / 0 20 20 0 
ctb 22 36 28 40 / 0 20 20 0 
hln 22 38 28 39 / 0 40 30 10 
bzn 9 36 17 35 / 0 60 40 10 
wey 3 27 11 26 / 30 90 80 20 
dln 13 31 16 30 / 0 60 40 0 
hvr 19 41 25 45 / 20 20 10 10 
lwt 19 37 22 38 / 0 40 40 10 


&& 


Tfx watches/warnings/advisories... 
none. 


&& 


$$ 


Short term...hoenisch 
long term...coulston 
aviation...brusda 


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