Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 241021

Area Forecast Discussion
National Weather Service Great Falls MT
321 AM MST Fri Feb 24 2017


Today through Sunday...In short, temperatures remain a few
degrees below average through the weekend, while scattered snow
showers will develop at times across North-central and Southwest
MT. At large scales, a broad and nearly stationary longwave trough
persists across the western U.S.. A weak anticyclonic flow aloft
over eastern Montana splits the trough and inhibits the movement
of a remnant low stuck in this pattern. Cloud cover will persist
over the area today with scattered light snow flurries continuing
at times over southwest Montana associated with low level
convergence in a surface trough over southeast ID. This activity
has been dissipating overnight, but another round of snow shower
activity is expected to perk up this afternoon over southwest MT.
Snow accumulations should remain rather light, but will continue
to monitor for possible travel hazards through the day. The split
flow aloft finally collapses later tonight into Saturday as the
next upstream shortwave pushes across the state. Surface winds
turn westerly and downslope on Saturday night with pressure falls
over southern Alberta. A new round of moderate snowfall spreads
into the Northern Rockies from Canada on Sunday, possibly
producing light snow across N-central MT by late Sunday. PN

Sunday night through Friday...Medium range models are in fair
agreement on the overall large scale pattern this period, beginning
with an upper level trough over the western US early next week,
followed by a fast progression of shortwaves ejecting out of digging
trough in the Gulf of AK and moving swiftly east along the
US/Canadian border during the middle to latter parts of next week.
Temperatures remain below seasonal averages to start next week then
moderate back to seasonal averages later next week. Series of fast
moving shortwaves will send several clipper type lows along the US
Canadian border mid to late next week, with models still having some
difficulty with timing and strength of these features at this time
range. Potential for strong winds with the passage of these
features, particularly on Wed and Thurs of next week. Temperatures
could also fluctuate significantly across northern zones as warming
occurs under periods of strong winds with cold air briefly being
dragged south from ALberta behind the passage of these clipper
systems. Hoenisch



Regional analysis shows a slow moving area of low pressure over
eastern Idaho (near KIDA), while to the NE, high pressure was
located over southern Canada. North of the SFC low, an inverted
trough stretches north through much of central/SW MT. Within this
trough, areas of -SN have persisted much of the evening from KGTF to
KHVR. This area of -SN appears to be dissipating. In fact, latest
satellite imagery shows some decrease in the cloudcover across
central MT. Given the low level moisture in place there and lighter
winds, some BR/FG development will be possible. Confidence in BR/FG
isn`t high, though, given the lingering cloudcover, so for now I
just went with some decrease in VIS, but trends will be monitored
and TAFs will be amended if FG becomes more likely. Beyond tonight,
the question will be how far north the ID low can get before getting
pushed east by an incoming cold front (slated to arrive FRI
afternoon). The chance of snow with this low appears greatest for
KEKS/KBZN and later forecasts may need to lower CIGS/VIS at those
sites if new model guidance continues to trend further north with
the low. Otherwise, a cold front should sweep NW to SE across the
forecast area Friday afternoon/evening and may be accompanied by a
band of SHSN as it moves through. Martin


GTF  29  12  29  18 /  10  10  10  10
CTB  25   8  26  15 /  10  10  10  10
HLN  28  11  27  14 /  20  20  10  10
BZN  27  11  26  10 /  30  30  30  10
WEY  20   4  17   0 /  50  40  50  30
DLN  24  10  23   9 /  50  40  20  10
HVR  31  16  28  17 /  20  20  20  10
LWT  29  14  27  15 /  30  40  20  10



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