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fxus65 ktfx 081739 aaa 
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Area forecast discussion 
National Weather Service Great Falls Montana 
1040 am MST Thursday Jan 8 2009 


Update aviation secton... 
morning update... 


Frontal boundary sitting across the northeastern corner of the 
forecast area...with 40s across the lower elevations to the west 
and south...and teens to the east and north. The boundary sits 
from just west of the port of Wild Horse to just to the south and 
east of Havre and on southeast towards Lodgepole. Very sharp tight 
gradient in temperatures at this time...with precipitation starting to lighten 
up across the northeastern warned counties. Will let the warning 
go to the end of the expiration due to the ice on the roadways and 
the areas of light precipitation still possible. 


Chinooks will develop today and keep the temperatures up and also 
spreading the warmer air into the colder portions of the forecast 
area by late this afternoon ahead of the next system tonight. Have 
made some minor adjustments to temperatures/dew points to catch current 
trends...did so as well to winds which are lighter than previously 
forecast across much of north central Montana as of this time. Will 
hold slightly higher probability of precipitation across Blaine County to account for the 
back edge of the precipitation that should linger for a few more hours. 
Slightly lesser clouds just downwind of the northern Rocky Mountain 
front with some downsloping. 


&& 


Previous discussion... 
/issued 505 am MST Thursday Jan 8 2009/ 


Today through Friday night...active weather pattern to continue across 
the region through the next 24 hours with strong/moist west to 
northwest flow aloft continuing today followed by the passage of a 
shortwave trough and associated surface low pressure/Canadian cold 
front tonight across north central Montana. Warm front continues to 
slowly lift NE across eastern zones this morning with an associated 
band of precipitation to move through eastern counties by noon. 
Problem this morning is cold air remains trapped at lower 
elevations along th milk River Valley in hill and Blaine counties. 
Temperatures are in the teens at Havre and Chinook while 
observations in the Bears Paw Mountains show temperatures near or above 40 
degrees...leading to a freezing rain situation which will likely 
last through early this morning before the warm front 
passes...allowing temperatures to warm above freezing. Therefore have 
issued a Freezing Rain Advisory for hill and Blaine counties this 
morning. Otherwise another mild but windy day is in store for much 
of the area with orographic snow continuing over the Continental 
Divide and other High Mountain ranges of the forecast area with 
any significant accumulations confined to areas north of Rogers 
Pass along the Continental Divide...where a Winter Storm Warning 
continues through today for elevations above 5000 feet. Surface low 
pressure tracks east along the Canadian border late this 
afternoon...allowing a Canadian cold front to surge south across 
the border in its wake late this afternoon...and continue south 
through north central Montana this evening...before stalling over 
central Montana Friday morning. Expect a wind shift to the north 
followed by rapidly falling temperatures and snow/blowing snow behind the 
frontal passage with about 2-4 inches of new snow on the plains 
before snow tapers to flurries by early Friday morning. Have 
expanded the Winter Weather Advisory across much of north central Montana to 
highlight this and extended the Rocky Mountain front warning to 
encompass this event as well. Friday finally quiets down as weak 
ridging builds overhead at the surface and aloft along with drier 
conditions. Cold period is short lived however as SW surface pressure 
gradients develop by Friday afternoon...warming low levels up to 
near average levels by Friday afternoon and evening. Hoenisch 


Saturday and Sunday...northwest flow will continue and a broad 
Pacific Ridge should keep temperatures relatively warm across 
central Montana. The exact position of the ridge will determine 
whether or not we see some effects of an Arctic air mass moving 
south from central Canada however. There is a possibility of light 
snow Sunday...mainly near the Rocky Mountains and higher 
elevations...as some moisture moves across the region from the 
northwest. 


Monday through Thursday...an upper level high pressure ridge over 
the eastern Pacific and West Coast will remain fairly stationary 
until moving east over the Pacific northwest on Wednesday. This will 
keep the local area underneath unsettled...northwest flow aloft. The 
airmass will be quite moist Monday as a shortwave moves through the 
flow aloft and...at the surface...high pressure over Saskatchewan 
and eastern Montana will bring upslope flow across the plains. 
Drying will begin by Monday night but improvement in the east will 
be slow. The gradual movement of the ridge east will keep most of 
the region free from higher chances of precipitation...the northeast 
zones will have the best chance for precipitation as they remain along the 
boundary between the colder air to the northeast. Temperatures will remain 
near normals through the period. Zelzer 




&& 


Aviation... 
an upper level low pressure trough is moving onto the West Coast. 
Moist flow ahead of this system will keep a chance of precipitation across 
the area. Best chance for precipitation will be over The Rockies...where 
MVFR ceilings are expected...the freezing rain should be diminishing 
across Blaine County early this afternoon. A coldfront will move 
across the Canadian border this evening and bring strong...gusty 
winds and snow across the plains. IFR ceilings and visibilities are expected 
near and behind the front. These conditions should prevail 
overnight...with improving conditions after sunrise on Friday. Db 




&& 


Preliminary point temps/pops... 
gtf 47 6 30 25 / 10 80 30 0 
ctb 43 0 30 23 / 30 70 10 0 
hln 48 19 36 19 / 20 60 20 0 
bzn 49 24 36 12 / 20 20 30 0 
wey 38 14 25 -2 / 70 70 50 20 
dln 43 20 29 11 / 20 10 10 0 
hvr 38 -2 19 10 / 70 80 20 0 
lwt 45 8 27 12 / 30 80 40 0 


&& 


Tfx watches/warnings/advisories... 
Winter Storm Warning above 5000 feet until 5 am MST Friday for 
mtz009-048. 


Ice Storm Warning until 11 am MST this morning for mtz011-013- 
047. 


Winter Weather Advisory below 5000 feet from 3 PM this afternoon 
to 5 am MST Friday for mtz009-010-044-046. 


&& 


$$ 


Short term...hoenisch 
long term...zelzer/eg 
aviation...db 
update...schott 


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