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fxus65 ktfx 211210 
afdtfx 


Area forecast discussion 
National Weather Service Great Falls Montana 
510 am MST Sat Nov 21 2009 


..update to aviation... 


Discussion... 
today through Monday...progressive pattern will continue. One 
upper trough will move through the area today into this evening. A 
weak upper ridge will then move over the area by late tonight 
before another upper trough moves through the area Sunday night. 
Then the next upper ridge will approach the area late Monday. With 
the upper troughs expect snow over the mountains with a fair 
chance of some snow in the southwest valleys. For each upper 
trough do not see more than six inches of snow in the mountains 
while the valleys could receive up to an inch. Although do not 
plan on issuing any winter weather highlights at this point will 
continue to mention the snow in the hazardous weather outlook. 
Speaking of highlights have issued a High Wind Warning for the 
northern Rocky Mountain front and adjacent plains for today. It 
appears atmospheric mixing will be able to tap into 50 knot winds 
just above the surface at least this morning. With these weather 
systems downslope flow should keep the plains generally dry. The 
second upper trough is forecast to have more moisture than the 
first upper trough so will continue with the mention of a slight 
chance of snow for late Sunday and Sunday night. With the upper 
ridge approaching on Monday just expect some lingering snow 
showers over the mountains from Sunday nights system. Blank 


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 1210z. 
An upper level low pressure trough over the Pacific northwest will 
continue to obscure the mountain areas of western...southwest...and 
central Montana in clouds and snow showers this morning. The khln 
terminal may also lower to MVFR conditions in rain/snow showers at 
times this morning...while local upslope conditions at kbzn will 
lower conditions to IFR levels at times due to heavier snow showers. 
Precipitation will decrease during the afternoon as the upper trough 
moves into the area. Gusty westerly winds will also increase 
significantly this morning as an associated cold front moves east 
across the area. Winds will be especially strong along the east 
slopes of The Rockies...where gusts could reach 50 knots at times. 
However...the downslope effect of the winds over the plains of north 
central and central Montana will limit precipitation to an isolated 
shower or two at best there. An upper level ridge of high pressure 
will then move into the area after 00z Sunday for clearing skies and 
decreasing winds overnight. Coulston 


&& 


Preliminary point temps/pops... 
gtf 44 25 41 27 / 10 0 20 20 
ctb 42 23 39 26 / 10 0 20 20 
hln 43 23 41 26 / 20 0 30 30 
bzn 37 13 37 16 / 50 0 30 40 
wey 31 8 30 12 / 90 30 80 60 
dln 34 14 34 13 / 50 0 40 40 
hvr 48 19 45 25 / 10 10 10 10 
lwt 43 18 38 21 / 10 0 10 30 


&& 


Tfx watches/warnings/advisories... 
High Wind Warning until 5 PM MST this afternoon for mtz009-010. 


&& 


$$ 


Short term...blank 
long term...coulston 
aviation...coulston 


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