Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 181643
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
943 AM MST Sat Feb 18 2017

.UPDATE...

Radar continues to show widespread very light precipitation
across N-central MT. Isolated reports have been received of rain
reaching the surface. This activity will continue to drift north
and weak through the early afternoon. Earlier concerns for light
icing are now mitigated as surface temperatures have risen to at
least 32F across the area. Updated the forecast to add slight
chance for light rain over a wider area through early afternoon.
Elsewhere, freshened hourly forecast grids to better match
observed trends. Webcams for Monida and Raynolds passes in far SW
MT shows at least partial snow cover, so will keep the winter
weather advisory going. PN

 &&

.AVIATION...
Updated 1120z.

VFR conditions will generally continue over the forecast area
through at least the next 24 hours. A disturbance over the Big Belt
and Little Belt Mountains at 12z will continue to push north across
the Plains through 18z before entering Canada, bringing mainly
patchy virga snow/rain showers. Winds will generally be easterly
along the Hi-Line and southerly to the south toward Great Falls and
the north-south valleys of SW MT. These more easterly upslope winds
over the Hi-Line may help bring MVFR to occasionally IFR conditions
to the Hi-Line later this evening, especially toward the Rocky
Mountain Front and KCTB. Cassell

&&

.PREV DISCUSSION...
/ISSUED 420 AM MST Sat Feb 18 2017/

Rest of tonight through Sunday night...
A highly amplified storm system continues to make landfall along
the California coast this morning, and the splitting northern
stream of this system will be the major weather player for the
weekend. Closer to home, upper ridging has moved away to the north
and east overnight, leaving the region in increasingly moist
south to southwest flow in the middle and upper levels of the
atmosphere. The first in the series of shortwave disturbances has
traversed north across southwest MT overnight and will move north
across the Plains through the remainder of the morning hours. This
feature will have the potential to drop a few snowflakes or
raindrops and that`s about it from Great Falls north to the
Canadian border. The next more significant shortwave moves across
the area this evening into Sunday. The entire Great Falls CWA
will continue to reside in the warm sector for this system, so
outside of continued upslope snow or snow/rain mix along the
Divide and near the MT/ID/WY border areas (mainly from Monida Pass
east to West Yellowstone), any precipitation will not be long-lived
for any lengthy amount of time. The strongest in this series of
disturbances moves through the region late Sunday evening into the
overnight. However, increasing cross-barrier flow at the lower
levels will make it hard for any significant precipitation to
make it out onto the Plains, with the best potential for
accumulating snow and snow/rain mix remaining over Southwest
Montana, especially toward the mountain passes along the ID/WY
border. Cassell

Monday through Saturday...Shortwave ridging should make Monday dry
for most, while westerly and moist upslope flow should trigger snow
along the western aspects of the Continental Divide and Southwest MT
mountains. On Tuesday, a shortwave trough is still progged to move
eastward over the CWA, resulting in primarily rain showers at lower
elevations and snow for the mountains. On Wednesday, zonal flow
aloft should permit dry weather for most of the day in North-Central
MT, but some upslope snow showers may persist along the Continental
Divide. Wednesday evening, the next mid- to upper-level trough of
low pressure and associated colder air will begin overspreading
our region from the west. As this longwave trough moves eastward
over our area on Thursday, the track of the accompanying 700 mb
low pressure center still looks to remain south of the CWA, which
would favor snow across Southwest MT Wednesday night into
Thursday. Disagreement between the 00Z/Sat ECMWF and GFS grows
considerably for Friday and Saturday. The ECMWF suggests unsettled
northwesterly to northerly flow aloft will develop over the CWA
as the aforementioned mid- to upper-level longwave trough axis
exits North-Central and Southwest MT to the east. On the other
hand, the GFS depicts mid- to upper-level ridging building
eastward over our area Friday before being broken-down by a mid-
to upper-level trough dropping southward from Canada on Saturday.
For now, the Friday and Saturday forecast follows a blend of the
two model solutions to account for the increased uncertainty.

Temperatures will tend to be above normal Monday and Tuesday of
next week. On Wednesday, a cooling trend will begin and persist
through Saturday. Thus, temperatures will transition to below
normal, especially for Thursday through Saturday.
Jaszka

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  52  34  52  31 /  20  20  20  20
CTB  42  27  44  25 /  30  20  50  20
HLN  45  28  44  25 /  10  30  40  40
BZN  45  29  45  23 /  20  50  60  60
WEY  34  30  35  19 / 100  90 100  60
DLN  46  32  44  22 /  20  60  60  20
HVR  50  31  49  30 /  30  10  20  20
LWT  53  35  54  30 /  20  10  40  50

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 5 PM MST Sunday Beaverhead...
Gallatin...Madison.

&&

$$

weather.gov/greatfalls



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