Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 190312
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
812 PM MST Thu Jan 18 2018

.UPDATE...
Keeping a close eye on the radar this evening, as precipitation
has slowly progressed eastwards across the Plains as expected.
Observations across the region indicate many locations are still
above freezing as of 03z, with the exception of higher terrain
along the Divide, as well as a few mountain peaks in central MT.
Model soundings this evening continue to confidently illustrate
many locations changing over from light rain/drizzle to snow
through the night, especially for locations along and south of a
line from Augusta, to Great Falls, to Loma. For these locations
in central MT, rain and/or light snow will likely be short lived
as this area of precip slowly slides southwards with little to no
accumulation expected overnight. However, with the better part of
the precip shield pushing into SW MT later this morning, along
with cold air filtering in, there could be a very brief change
over from rain to perhaps some freezing drizzle before changing
over to all snow. Not anticipating any significant impacts due to
freezing rain, however snow totals ranging anywhere from 1 to 3
inches, with higher amounts reaching around 8 inches in higher
terrain will be possible in this region through Friday morning.
Additionally, with previously warmer afternoon temperatures the
past few days across central and southwestern MT, combined with
early onset light rain, roads will be wet and with freezing
temperatures expected, some area roadways may ice over which may
lead to difficult travel in some spots early Friday morning. No
additional changes to the current winter weather highlights were
necessary in this update package as the forecast remains on track.
KLG

&&

.SYNOPSIS...
Snow along the Rocky Mountain Front will overspread portions of
Central Montana and all of Southwest Montana this evening and
persist into Friday. Precipitation may begin as rain or freezing
rain before quickly changing to snow. Temperatures will cool
gradually through early next week and the potential of snow
showers will continue, especially along the Continental Divide.

&&

.AVIATION...
Updated 2315Z.

Ceilings and visibilities are expected to lower/decrease through the
1900/2000 TAF period across Southwest and North Central Montana, as
precipitation associated with a passing disturbance overspreads the
region, especially south of a KCTB to KHVR line. VFR conditions are
generally expected at the KCTB and KHVR terminals, with MVFR and at
times IFR conditions expected for the KGTF, KLWT, KHLN, KBZN, and
KEKS terminals. There does exist the potential for a brief period of
freezing rain with the onset of precipitation this evening at the
KHLN, KBZN, and KEKS terminals, however, confidence was not high
enough to insert this mention within the actual forecast. Mountain
obscuration is likely this evening and tomorrow morning, especially
along the Continental Divide and over Central and Southwest Montana.
Mountain wave induced turbulence is also possible, especially near
the Rocky Mountain Front. Precipitation chances are then expected to
decrease from north to south through the morning and into the
evening hours on Friday. - Moldan

&&

.PREV DISCUSSION...
/ISSUED 415 PM MST Thu Jan 18 2018/

Rest of today through Sunday...A Pacific cold front, most
pronounced just above the surface, will continue moving
southeastward over North-Central MT and exit the entire CWA by
daybreak Friday. Simultaneously, a Pacific trough aloft will
cross our area Friday evening through Saturday evening and be
followed by high pressure aloft building-in from the west by
Sunday. This pattern will cause our temperatures to cool gradually
through the upcoming weekend.

The above pattern will allow periods of upslope snow to persist
along the Continental Divide through this weekend, especially
along the Rocky Mountain Front. The bulk of this accumulating snow
is expected to continue through Friday morning; hence the winter
weather advisory. As the aforementioned cold front moves through
and the Pacific trough approaches, a few rain and/or wet snow
showers are possible over the North-Central MT plains, along and
north of a Great Falls to Lewistown line, this evening into
Friday. However, little or no snow accumulation is expected.
Farther south, winter weather advisories have been posted for this
evening into Friday morning. Here, precipitation may begin as
rain before quickly changing to accumulating snow as cold
advection follows the frontal passage. In addition, a brief period
of freezing rain is possible this evening for valley locations,
especially those from Helena through Townsend to Bozeman.
However, any ice accumulations are expected to be a light glaze at
most. Please see the winter weather advisory statements for
further details. Besides the aforementioned snow along the
Continental Divide, the remainder of the CWA is expected to have
little or no precipitation Friday night through this weekend.
Jaszka

Sunday night through Thursday...The weather pattern will be a
more progressive one through Tuesday, as disturbances bring a
chance of snow mainly to the mountains. Lower elevations will
likely remain dry with breezy southwest winds over the plains. The
best chance for precipitation at lower elevations during this
time will be associated with a shortwave trough passage Sunday
night into Monday, but amounts appear to remain light at this
time. Temperatures will also remain a few degrees below normal
through this time. A large and broad upper-level low pressure
trough will then move southeast over the western United States
Wednesday through Thursday, which will cool temperatures further
below normal (highs mostly 20s; lows mostly single digits and
teens) and bring a chance of snow to most of the area. Again,
however, the main threat for measurable snow will remain in the
mountains, where exact amounts are uncertain at this time.
Coulston

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  33  40  23  34 /  40  20  10  10
CTB  28  37  23  34 /  10  10  10  10
HLN  30  33  15  26 /  70  40  10  10
BZN  32  35  12  25 /  80  60  30  10
WEY  31  32   4  23 /  90  90  50  20
DLN  31  37  12  27 /  50  40  10  10
HVR  29  36  16  28 /  20  10  10  10
LWT  31  37  18  31 /  70  40  20   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 11 AM MST Friday Northern Rocky
Mountain Front...Southern Rocky Mountain Front.

Winter Weather Advisory until 11 AM MST Friday Broadwater...
Cascade...Central and Southern Lewis and Clark...Jefferson...
Judith Basin...Meagher.

Winter Weather Advisory until 11 AM MST Friday Beaverhead...
Gallatin...Madison.

&&

$$

http://www.weather.gov/greatfalls


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