Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 260047

Area Forecast Discussion
National Weather Service Great Falls MT
545 PM MST Sat Feb 25 2017



Tonight through Monday...A shortwave trough over northern BC and
vicinity this afternoon is expected to move southeastward and cross
our CWA Monday morning through afternoon. At the surface, a cold
front accompanying the shortwave is expected to advance southward
across the Canada border Sunday morning and should then stall along
the mountains in vicinity of Great Falls and Helena Sunday evening.
Lift ahead of the approaching shortwave trough amidst sufficient
moisture should trigger periods of light snow across the CWA during
the period. In addition, enhanced lift and pockets of weak
instability along the cold front are expected to trigger a narrow
band of heavy snow along the Rocky Mountain Front later Sunday
morning through evening. Thus, issued a winter weather advisory for
the Northern and Southern Rocky Mountain Front, including Marias
Pass. Snowfall rates may reach 1 inch per hour within the snow band,
resulting in a brief burst of heavy snow and difficult driving
conditions. This southward-moving snow band may extend farther
eastward and impact much of the North-Central MT plains for a short
period of time Sunday. However, confidence in this scenario is low.

Will have to monitor the central third of our forecast area for
steadier snow Sunday night into Monday, where enhanced lift and
somewhat heavier snowfall rates are possible along the stalled
front. Also, some mesoscale model guidance suggests low- to
midlevel frontogenetical forcing for ascent ahead of the shortwave
trough may trigger localized snow bands over far-southern
Southwest MT Sunday evening into Monday. Will hold-off on issuing
highlights for these areas, but later shifts will have to
reevaluate steadier snowfall potential in these areas. Below-
normal temperatures are expected throughout the period.

Monday Night through Saturday...Upper level trough axis shifts east
across the Northern Rockies and MT Monday night and Tuesday with
weak low pressure tracking east through central MT. Moisture is
fairly limited but a marginally unstable airmass and weak energy
associated with the upper trough should provide enough lift for
scattered snow showers continuing through Tuesday before drier and
more stable air moves in with a building upper level ridge Tuesday
night. Fast moving shortwave and upper level jet push east along the
US Canadian border Wed/Wed night for a period of increasing winds
and moderating temperatures. Some cold air will spill back south
across northern zones Wednesday night through Thursday morning
behind a clipper type surface low that moves east into the Dakotas
this period. Warming ensues for Thursday and Friday as upper level
ridge rebuilds ahead of the next shortwave moving in from the Gulf
of AK. Medium range models continue to advertise fairly deep surface
low emerging across the Canadian Prairies Friday night as this
energy moves across the Rockies with a strong upper level jet
punching east across MT. This is a favorable setup for strong winds
across the region with very strong winds currently depicted by GFS
model, though EC/CMC solutions are not as extreme at this point.
Situation will continue to be monitored through the upcoming week.



A northwest flow aloft will continue mountain-obscuring snow along
the Rocky Mountain Front through the period. Otherwise, an exiting
disturbance in the flow will bring decreasing clouds, showers, and
winds to the remainder of the area through 06Z. However, clouds and
snow will increase over the area between 06Z and 12Z, especially
over North Central Montana, as a shortwave trough will approach the
Pacific Northwest, putting the area under an increasingly moist
southwest flow aloft. A Canadian cold front will then move south
over North Central Montana between 09Z and 15Z, shifting winds more
northerly there and gradually lowering flight conditions from mostly
VFR to mostly MVFR/IFR by 15Z, which should continue through at
least the rest of Sunday. The cold front, and consequently the lower
flight conditions and snow, will be slower to reach far Southwest
Montana (including KBZN and KEKS), likely not until after 12Z.


GTF  21  28   9  24 /  30  70  60  40
CTB  19  21   4  18 /  40  70  50  40
HLN  20  29   8  24 /  20  60  60  30
BZN  16  27  11  25 /  10  20  30  40
WEY   6  18   7  21 /  40  40  70  60
DLN  13  25  12  26 /  10  20  30  30
HVR  20  27  10  23 /  30  30  50  30
LWT  18  27  11  23 /  20  40  60  40


Winter Weather Advisory from 2 AM to 11 PM MST Sunday Northern
Rocky Mountain Front.

Winter Weather Advisory from 8 AM to 11 PM MST Sunday Southern
Rocky Mountain Front.


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