Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 230238
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
838 PM MDT Fri Mar 22 2024

.SYNOPSIS...

Areas of light snow will continue through tonight across north-
central Montana where a colder airmass remains in place. A
Pacific weather system then spreads more significant and
widespread snow across the area late Saturday and Sunday with a
period of moderate to heavy snow likely across some areas
Saturday night. Temperatures will continue to cool through the
weekend with coldest conditions likely Sunday and Sunday night.

&&

.UPDATE...

No significant updates to the ongoing forecast or the winter
weather advisories/warnings. The main concern overnight will be
the persistent band of light snow that is expected to linger over
the plains of North Central and Central Montana. Additional
accumulations should mostly remain light, as most areas should
receive an additional 0.5 to 1.5 inches of snowfall. The only
adjustment was to increase probabilities of precipitation where
those accumulations should occur. Otherwise, temperatures are
trending in the right direction. -Coulston

&&

.AVIATION...
555 PM MDT Fri Mar 22 2024 (23/00Z TAF Period)

North Central (KCTB KHVR) and much of Central (KGTF KLWT)
Montana: Widespread light snow and low clouds will continue
mountain-obscuring MVFR/IFR conditions over the area through at
least 24/00Z. The main area of snow will move north more so onto
the Hi-Line after 12Z, but snow will increase again from the
southwest after 18Z. Gusty easterly winds may also cause periods
of blowing snow at the eastern TFX terminals (KHVR KLWT).

Southwest (KBZN KEKS) and a portion of Central (KHLN) Montana:
VFR conditions are expected to continue through at least 23/18Z.
However, a few rain or snow showers may move through the area
through 06Z, and MVFR ceilings may spread south into the KHLN
valley area between 12Z and 18Z. After 18Z, the moisture
responsible for the snow mentioned for North Central Montana will
move northeast into the area. However, warmer temperatures will
cause weak instability to develop, causing more showery rain and
snow with periods of MVFR conditions. The instability may also
cause a few isolated thunderstorms, mainly along and south of
Interstate 90, but at this time, confidence is low that any
thunderstorms that may develop will directly impact any of the
terminals. -Coulston

Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.

&&

.PREV DISCUSSION...
/ISSUED 555 PM MDT Fri Mar 22 2024/

Rest of this afternoon through Sunday night...A potent spring
storm will bring accumulating snow to all of Southwest through
North Central Montana through the weekend, with below to well
below normal temperatures settling in across all of the region
through Saturday evening/overnight. Light to at times moderate
snow has been on- going over portions of Central and North
Central Montana throughout the day, with this snow expected to
persist into the morning hours on Saturday as mid-level
frontogenesis pivots north to northwestward ahead of the
approaching upper level disturbance. Winter Weather Advisories
remain in effect for areas north/northwest of a Rogers Pass, to
Carter, to Hays line for this continued period of snow, with
additional accumulations of generally 1-2" expected through 6am
Saturday.

By Saturday morning the upper level trough will begin to move
from over the Eastern Pacific to over the Pacific Northwest
before moving east over the Rockies through the day on Sunday. A
brief lull in precipitation is possible during the mid- to late
morning hours on Saturday in wake of strong mid- to upper level
warm air advection; however, this will be short-lived as
additional precipitation lifts northeastward through the early to
mid- afternoon hours. Precipitation may initially begin as rain
in Southwest and Central Montana over this timeframe, but quickly
transition to snow due to strong cooling. The highest chance for
moderate to heavy snow falling across all of Southwest through
North Central Montana will be from the early evening hours on
Saturday through the mid-morning hours on Sunday as the best
upper level divergence and mid-level frontogenesis lifts and
pivots across the region, especially for areas southwest of a
Dillon, to Helena, to Great Falls, to Chinook line. With the
exception of Northern Blaine, The Bears Paw Mountains, Fergus
County below 4500ft, and the Snowy Mountains where a Winter Storm
Warning is now in effect, a Winter Weather Advisory now covers
all of Southwest through north Central Montana from 18/21z
Saturday through 00/06z Monday. One area that will need to be
watched will be across Southwest into portions of Central Montana
as Hi-Res guidance continues to indicate an intense band of
precipitation lifting northeastward Saturday evening and night,
generally east of a Dillon, to Helena, to Kings Hill Pass line.
Should this band actually materialize then snowfall rates in
excess of 1" per hour could be possible for a time, which may
require an upgrade from the Winter Weather Advisory to a Winter
Storm Warning. This spring storm will bring a multitude of
impacts to the Northern Rockies, including but not limited to
hazardous driving conditions and severe to extreme condtions to
newborn livestock. - Moldan

Monday through Friday... Light mountain snowfall continues
throughout next week with a brief break in precipitation for
Wednesday as weak upper level ridging moves through our area then
ensemble member guidance is supporting for upper level troughing
to return for later next week. While still much uncertainty
remains for where troughing can occur exactly, probabilities from
latest National Blend of Models 4.1 data are above 50% for 24
hour snowfall (Thursday into Friday) amounts exceeding 4 inches
for Southwest Montana mountain ranges. Lower elevations are near
50% for a half inch of snowfall but with still much uncertainty
this far out, it will continue to fluctuate through the week with
the upcoming forecast model guidance. Temperatures for Monday
will still be colder than forecasted from the deterministic NBM
for Glacier county to Blaine County due to cloud coverage and
recent snowfall, so made minor adjustments to lower high
temperatures Monday 5 to 10 degrees. But I do want to mention
that the National Blend of Models 4.1 data is catching up to what
we are thinking for the long term, with a slow warm up across the
Hi- Line and everywhere else being near normal for temperatures
next week until later in the week where greater uncertainty
remains for temperatures. Webb

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  22  29  13  21 /  90  90 100  90
CTB  15  23  12  20 / 100  90  90  60
HLN  26  38  19  25 /  20  80  90  70
BZN  26  47  18  29 /  20  80  90  70
WYS  25  45  21  30 /  20  80  90  70
DLN  31  52  23  31 /  10  90 100  60
HVR  13  24  10  21 / 100  90 100  80
LWT  17  30  10  18 /  90  70 100  90

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 AM MDT Saturday for Bears Paw
Mountains and Southern Blaine-East Glacier Park Region-Eastern
Glacier, Western Toole, and Central Pondera-Eastern Pondera and
Eastern Teton-Eastern Toole and Liberty-Hill County-Northern
High Plains-Southern High Plains-Southern Rocky Mountain Front-
Western and Central Chouteau County.

Winter Weather Advisory from noon Saturday to 6 PM MDT Sunday
for East Glacier Park Region-Eastern Glacier, Western Toole, and
Central Pondera-Eastern Pondera and Eastern Teton-Eastern Toole
and Liberty-Hill County-Northern High Plains-Southern High
Plains-Southern Rocky Mountain Front.

Winter Storm Warning from 3 PM Saturday to midnight MDT Sunday
night for Bears Paw Mountains and Southern Blaine-Fergus County
below 4500ft-Northern Blaine County-Snowy and Judith Mountains.

Winter Weather Advisory from 3 PM Saturday to 6 PM MDT Sunday
for Beaverhead and Western Madison below 6000ft-Big Belt,
Bridger and Castle Mountains-Canyon Ferry Area-Cascade County
below 5000ft-Elkhorn and Boulder Mountains-Gallatin Valley-
Gallatin and Madison County Mountains and Centennial Mountains-
Gates of the Mountains-Helena Valley-Judith Basin County and
Judith Gap-Little Belt and Highwood Mountains-Madison River
Valley-Meagher County Valleys-Missouri Headwaters-Northwest
Beaverhead County-Ruby Mountains and Southern Beaverhead
Mountains-Upper Blackfoot and MacDonald Pass-Western and Central
Chouteau County.

&&

$$

http://www.weather.gov/greatfalls


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