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FXUS65 KTFX 230342
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
842 PM MST Tue Jan 22 2019


.SYNOPSIS...

Snow will move into the mountains early tomorrow morning, and then
spread to lower elevations through the day Wednesday. A cold
front will push south through the state Wednesday afternoon and
night, and snow will end overnight. High pressure will bring some
clearing Thursday, but with areas of blowing snow. Another system
may bring some mountain snow Friday.

&&

.UPDATE...

Some minor edits were made to the grids this evening but the
overall trend of the forecast remains on track. Snow is expected
to begin to pick up around 6Z along the Rocky Mountain Front and
in the mountains of the southwest. This activity will expand to
include north central areas by morning. Snow packed and slippery
roadways along with reduced visibilities due to falling/blowing
snow will be common especially during the day on Wednesday. The
current winter weather headlines handle the expected impacts from
this storm well. rcg


&&

.AVIATION...
Updated 0000Z.

There will be increasing mostly mid and high level cloudiness ahead
of the next weather system. Expect low clouds followed by developing
snow along with MVFR and possible IFR conditions around 5 to 6Z for
the SW terminals and along the Rocky Mountain Front. This area of
precipitation and low clouds will then will then expand toward the
other terminals around 11 to 12Z. Widespread snow, heavy at times is
expected to persist for much of the day across for all terminals
with the exception of KHVR and KCTB where the snow will be much
lighter and scattered in nature. As a result, expect MVFR/IFR
conditions and mountain obscuration. rcg

&&

.PREV DISCUSSION...
/ISSUED 510 PM MST Tue Jan 22 2019/

Lee-side pressure falls generated strong winds today along and
adjacent to the Rocky Mountain Front. The winds caused drifting
and blowing snow in these areas. Conditions will improve overnight
as snow becomes scoured and winds gradually weaken.

The next shortwave arrives Wednesday on a strong northwest flow
aloft. The wave tracks through central MT as an open wave at 700
mb, but will have good lift associated with the passing upper
level jet streak and favorable interaction with terrain. Snow will
develop late tonight over the northern Rocky Mountains, then
spread across the central and southwest mountains by early morning
Wednesday. The period of heaviest snowfall is expected from mid-
morning through late afternoon. Snowfall amounts over the
mountains may exceed a foot in some areas, particularly over Kings
Hill Pass in the Little Belt Mountains, the Big Belt Mountains,
the Bridger Range, and the Madison Range. The Winter Weather
Advisory posted for these areas has been elevated to a Winter
Storm Warning. Expect significant impacts to travel along Highway
87, Highway 89, and Interstate 90 over Bozeman Pass. A cold front
associated with the passing wave will advance from north to south
Wednesday afternoon. A period of heavier snowfall may be
associated with the passing front. Furthermore, the northwesterly
flow behind the front could produce a longer period of snow over
the northern slopes of the the Little Belt Mountains. Overall
snowfall amounts have increased across central MT with this
update, and we continue to expect heavy snow in the the favorable
northwest flow for the central and southwest Mountain ranges. Snow
gradually tapers Wednesday night into early Thursday.

Thursday through Tuesday... Northwest flow aloft dominates the
period with a large scale pattern featuring an upper level ridge
just off of the west coast and deep upper trough over central
Canada. A surface trough to the lee/east of the Rockies will keep
the main cold airmass beneath the upper trough east of the region
through Saturday while also supporting breezy to windy conditions
at times, especially across western portions of north-central MT.
Temperatures begin near seasonal averages Thursday, then warm to
above seasonal averages by Saturday. Generally weak shortwave
energy embedded within the NW flow aloft will bring a slight
chance of some mountain snow showers late Thursday and again
Saturday, though confidence in the timing of these features in not
great due to model differences. Models do however continue to
generally support the idea of a stronger shortwave to drop south
through the region during the Sunday/Sunday night timeframe, which
would bring another round of accumulating snowfall along with a
surge of colder air. Hoenisch

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF 27 35 8 35 / 50 90 70 0
CTB 22 30 3 34 / 60 70 20 0
HLN 23 35 13 34 / 50 90 60 0
BZN 20 32 14 33 / 60 90 80 20
WEY 7 22 4 24 / 90 100 90 30
DLN 21 36 21 35 / 30 30 30 0
HVR 16 29 -2 27 / 20 40 30 0
LWT 23 33 5 33 / 40 100 80 0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 11 PM MST Wednesday Beaverhead...
Broadwater...Central and Southern Lewis and Clark...Eastern
Teton...Jefferson...Madison...Northern Rocky Mountain Front...
Southern Rocky Mountain Front.

Winter Storm Warning until 5 AM MST Thursday Cascade...
Gallatin...Judith Basin...Meagher.

Winter Weather Advisory from 5 AM Wednesday to 5 AM MST Thursday
Chouteau...Fergus.

&&

$$

http://www.weather.gov/greatfalls
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