971 
fxus65 ktfx 211751 
afdtfx 


Area forecast discussion 
National Weather Service Great Falls Montana 
1040 am MST Sat Nov 21 2009 


Aviation section updated 


Update... 
upper level trough is progressing across the region this morning 
while the associated Pacific cold front has moved through all zones 
and will continue to progress east into the Dakotas by this 
afternoon. A period of snow occurred with the frontal passage 
across much of SW Montana early this morning...with only impact across 
northern zones being a shift to more westerly winds. Winds aloft 
remain fairly strong and cold advection through today will promote 
mixing of those stronger winds down to the surface across northern 
zones through this afternoon. Strongest winds will be along the 
northern Rocky Mountain front and Glacier County...however the period 
of peak winds aloft has passed. Still expect sustained winds 
near 30kts at times so will let the High Wind Warning continue for 
those areas through this afternoon. Unstable and somewhat moist 
westerly flow will maintain scattered mountain snow showers this 
afternoon with more persistent shower activity expected over the 
Gallatin/Madison ranges of SW Montana where an inch or two of new snow 
may fall through this afternoon. Elsewhere...downslope westerly 
flow will limit precipitation chances with partly cloudy skies 
across western portions of north central Montana. One exception may be 
areas along the Canadian border later this afternoon as a disturbance 
dropping southeast from Alberta may produce a few light snow showers or 
flurries. Have made some minor adjustments to probability of precipitation to account for 
this and align with latest observational trends. Otherwise...current 
forecast is in good shape. Hoenisch 


&& 


Aviation... 
updated 1740z. 
An upper level low pressure trough will continue to make its way 
across central Montana this aftn/eve. Most of associated moisture has 
already pushed toward kbil but locations west of a kbil-to-khln line 
will see a few residual snowshowers through mid-aftn. Ceilings 
should remain VFR across the region...though higher terrain will be 
obscured with MVFR/IFR conditions near any precipitation areas. 
Winds will be gusty over the plains and Rocky Mountain front this afternoon 
with widespread gusts of 25 to 35 kts...and some locations from 
Glacier np to khvr seeing gusts of 40 to 50 kts. As the trough 
moves further east this evening...winds should decrease toward sunset 
and skies will be mostly clear overnight at all terminals. 
Waranauskas 


&& 


Previous discussion... 
/issued 510 am MST Sat Nov 21 2009/ 
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 


&& 


Preliminary point temps/pops... 
gtf 44 25 41 27 / 10 0 20 20 
ctb 42 23 39 26 / 0 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 / 40 0 40 40 
hvr 48 19 45 25 / 20 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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