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fxus65 ktfx 120253 
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Area forecast discussion 
National Weather Service Great Falls Montana 
845 PM MDT Sat Oct 11 2008 


Discussion... 
will update forecast this evening to mainly freshen forecast 
wording. Have made minor adjustments to pop grids to align with 
neighboring offices. Snow event continues but it has become 
increasingly apparent event is significant primarily for higher 
terrain. Have lowered snow amounts in the warning itself for the 
valleys and lower terrain. Heaviest amounts will contiue over the 
eastern counties of the County Warning Area tonight and into Sunday. 
Emanuel 


&& 


Aviation... 
updated 0240z. 
A deep upper level trough of low pressure...currently over the 
eastern Great Basin...will slowly lift NE across Wyoming and eastern Montana 
and into southern Canada during the next 24 hours. This will maintain 
a very moist flow aloft over the region...shifting from the southeast to 
the east and eventually north by Sunday afternoon. Widespread snow and 
MVFR/IFR conditions will persist at at the kbzn and klwt terminals 
through the period with heaviest precipitation and lowest ceilings 
expected at klwt later tonight through Sunday morning. Somewhat 
better conditions will persist farther to the northwest at khln and kgtf 
where occasional MVFR/IFR conditions are expected in bands of snow 
near the periphery of the system with VFR conditions prevailing at 
kctb and khvr through Sunday farthest away from the system. Mountain 
obscurations will exist across all of the the area with surface 
winds generally from the east to NE through the next 24 hours. Britton 


&& 


Previous discussion...issued 240 PM MDT Sat Oct 11 2008 


Tonight through Monday...strong upper level low south of Montana 
will begin to swing to the northeast tonight...moving through 
eastern Montana on Sunday. Snow will continue to strongly impact 
the mountains of southwest Montana and southern portions of 
central Montana overnight and through the day on Sunday. Have had 
reports of as much as three feet accumulation along the eastern 
slopes of mountain ranges in southwest Montana. However..lower 
elevations of the warning area are more problematic as orographic 
shadowing is blocking much of the precipitation and warmer 
temperatures are causing what snow does fall to melt. Warning will 
be left intact...but intend to reword product to make it more 
generally understood that lower elevations will probably not get 
abundant accumulations. Possible exception will be Fergus County 
where models continue to show strong moisture advection through 
eastern Montana as the low lifts northeast through the region. 
Also...Blaine County is not expected to receive more than a chance 
of snow overnight so have opted to delay the beginning time of the 
warning in this zone until morning. Precipitation will rapidly 
taper off from west to east as the storm system moves through the 
area. By Monday afternoon expect only residual areas of cloudiness 
with temperatures warming back up into the 40s and 50s. Mpj 


Monday night through Thursday night...models indicating that last 
remnants of the large upper level storm system from the weekend 
gradually depart to the east Monday night. Locations east of Havre to 
Bozeman line may see a few lingering snow flurries as system exits 
the area. West-northwesterly flow pattern on Tuesday should produce 
broad area of downslope/drier conditions. Weak instability 
associated with minor waves in the flow may bring a few 
rainshowers and mountain snowshowers on Wednesday. Both GFS and European 
models show a better-defined Pacific shortwave trough moving across 
northern/central Montana on Thursday with light snow along the Highline... 
rain/snow mix around/east of Great Falls...and light rain from 
Helena to Lewistown. No appreciable warm air advection is apparent 
during this period so look for afternoon highs to stay 4 to 8 degree 
below normal. Waranauskas 


Friday and Saturday...a disturbance in a northwest flow moves east 
out of the zones Thursday allowing high pressure to build in from 
the west. A zonal flow sets up ahead of the next Pacific system by 
Friday. Saucier 


&& 


Preliminary point temps/pops... 
gtf 24 35 24 48 / 60 50 10 10 
ctb 19 42 26 56 / 20 10 0 0 
hln 28 39 22 48 / 50 50 20 10 
bzn 26 39 19 46 / 60 60 40 10 
wey 19 30 8 35 / 100 60 30 10 
dln 20 33 17 40 / 90 60 20 10 
hvr 21 40 22 51 / 30 30 60 10 
lwt 21 31 19 39 / 90 90 50 10 


&& 


Tfx watches/warnings/advisories... 
Winter Storm Warning until 6 PM MDT Sunday for mtz008-012-014- 
015-050-052>055. 


Winter Storm Warning from 6 am Sunday to 6 am MDT Monday for 
mtz047. 


Winter Storm Warning until 6 am MDT Monday for mtz051. 


&& 


$$ 


Short term...Emanuel/mpj 
long term...waranauskas/Saucier 
aviation...Britton 


Weather.Gov/greatfalls