Winter Storm Warning 6, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
1045 PM MST Wed Mar 8 2023

Updated Aviation Discussion

.SYNOPSIS...
Light east to northeasterly flow at the surface will maintain low
clouds, patchy fog, and periods of light snow through Thursday
morning, especially over the plains. A stronger Pacific system and
an attendant cold front arrives Friday into Saturday and brings
gusty winds, snow, and even some mixed precipitation for the first
half of the weekend. High pressure and drier conditions are expected
Sunday into early next week, with temperatures warming back to near
average by Monday.

&&

.UPDATE...
Updated forecast is out. Light snow continues to fall over much of
North Central MT this evening. Pops were adjusted up. Snowfall
rates are around 0.2 inches per hour. Thus another 1 to 2 inches
of snowfall overnight looks on track for North Central MT, and the
winter weather advisory will continue. Scattered snow showers
will develop over Southwest MT, mostly after Midnight. Most of the
snow should exit the CWA by mid morning Thursday. A short dry
period expected Thursday afternoon, then a strong system will move
into the CWA for Thursday night/Friday with wind/snow concerns.
The period of heaviest snowfall looks to be Friday afternoon and
evening, likely having an impact on the Friday evening commute.
Snowfall rates could approach 1 inch per hour during the peak period
of heavy snowfall. Winter storm/high wind watches have been issued
for Southwest MT for this event, with additional winter highlights
likely further north. Brusda

&&

.AVIATION...
1045 PM MST Wed Mar 8 2023 (09/06Z TAF Period)

Low clouds and areas of light snow persist across most of the area
tonight with IFR ceilings/visibility most widespread across north-
central MT while MVFR to occasional IFR is expected across SW MT.
Areas of light snow diminish early Thursday morning for most areas
with improving ceilings later Thursday morning, though low clouds
may persist later across north-central MT. Hoenisch

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

&&

.PREV DISCUSSION...
/ISSUED 300 PM MST Wed Mar 8 2023/ Remainder of this afternoon
through Thursday...Shortwaves rotating around a broad Pacific
trough will combine with east/northeasterly upslope flow for
continued periods of light snow over much of Central/North-Central
Montana through Thursday morning. Model guidance has struggled
with the situation and will likely continue to do so for the
remainder of the event. The persistent snow and the anticipation
of wet roads freezing up this evening has prompted me to expand
the Winter Weather Advisory to include all of North- Central
Montana and make it effective immediately. Snow totals aren't very
impressive to say the least, but impacts are anticipated given
the aforementioned factors. Southwestern locations are expected to
see snow as well tonight, but it looks to be a little less
consistent, so I held off on issuing highlights there. Snow is
expected to quickly diminish Thursday morning, yielding a brief
quiet period through Thursday evening.

Thursday evening through Saturday night...Moisture ahead of the
next shortwave trough will approach the region Thursday night.
Snow and some mixed precipitation will move form southwest to
northeast Thursday night into Friday. All locations will have at
least some impacts from winter weather Friday into Saturday as a
warm front followed by a vigorous Pacific cold front traverse the
region. For now I concentrated on the areas that are anticipated
to be impacted the most, namely Southwestern Montana. Areas south
of I90 will be impacted by strong winds and or snow. Probabilities
of wind gusts over 55 mph are exceeding 50% for the north to
south oriented valleys and some mountain areas south of I90. This
will occur as a stripe of 50 kt + H700 winds funnel ahead of the
Pacific cold front. A High Wind Watch was issued for zones 328 and
325 (Dillon/Ennis valleys), which runs from 11 pm MST Thursday
through 5 am MST Saturday. For areas expecting snow, zones 329/330
(Gallatin/Madison ranges/Southern Beaverhead/Ruby Mountains), a
Winter Storm Watch was issued form 5 pm MST Thursday through 5 am
MST Saturday morning. The heaviest snow will be over mountain
areas and the West Yellowstone area, but I'm very concerned about
significant blowing snow issues over the Monida Pass area despite
lower forecast totals. Snow will wrap up for most locations on
Saturday, except along the immediate eastern slopes for the Rocky
Mountain Front. Also, gusty winds will persist through the day on
Saturday as strong westerly flow continues in the wake of the
passing front.

Sunday through next Wednesday...Ensembles are in good agreement
with upper level ridging building in Sunday through early Tuesday,
resulting in drier conditions. Temperatures will moderate to near
or slightly above average by Monday, though the warm up will
initially be slowed by low level easterly flow, especially over
the plains on Sunday. The next shortwave, cooler temperatures, and
chance for snow arrives late Tuesday into Wednesday. -RCG

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  11  29  17  33 / 100  40  10  60
CTB   4  22  10  25 / 100  40  10  70
HLN   9  33  20  43 /  40  10  10  60
BZN   7  30  15  43 /  40  10  20  60
WYS   1  26  11  37 /  50  30  80 100
DLN   7  30  20  42 /  20  10  20  60
HVR   8  22  10  27 / 100  50   0  70
LWT  10  24  13  33 / 100  50  10  70

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 9 AM MST Thursday for Bears Paw
Mountains and Southern Blaine-Cascade County below 5000ft-East
Glacier Park Region-Eastern Glacier, Western Toole, and Central
Pondera-Eastern Pondera and Eastern Teton-Eastern Toole and
Liberty-Fergus County below 4500ft-Gates of the Mountains-Hill
County-Judith Basin County and Judith Gap-Little Belt and
Highwood Mountains-Northern Blaine County-Northern High Plains-
Snowy and Judith Mountains-Southern High Plains-Southern Rocky
Mountain Front-Western and Central Chouteau County.

Winter Storm Watch from Thursday afternoon through late Friday
night for Gallatin and Madison County Mountains and Centennial
Mountains-Ruby Mountains and Southern Beaverhead Mountains.

High Wind Watch from Thursday evening through late Friday night
for Beaverhead and Western Madison below 6000ft-Madison River
Valley.

&&

http://www.weather.gov/greatfalls