NWS Great Falls, MT wrote its last area forecast discussion before the first event at Dec 2, 8:11 AM MST, 1 hour 49 minutes earlier.
Area forecast discussion, Dec 2, 8:11 AM MST, 1 hour 49 minutes before
Area Forecast Discussion
National Weather Service Great Falls MT
811 AM MST Fri Dec 2 2022
.SYNOPSIS...
Snow will end from northwest to southeast across the Northern
Rockies through the day today. Cold temperatures are expected
across all of Southwest through North Central Montana today, with
increasing southerly winds along the Rocky Mountain Front, Montana
Hwy 200 corridor, and in the Madison Valley. These increasing
winds will likely lead to drifting and blowing snow, which could
lead to partial lane blockages and reduced visibility.
&&
.UPDATE...
Main adjustment this morning was to end the winter storm warning
for the West Yellowstone area, and then extend the wind chill
advisory for the Highway 2 corridor from Cut Bank to Harlem until
11 AM Saturday. Otherwise, blowing snow likely to develop later
today along the front range of the Rockies and gradually spread
out over the Plains tonight into Saturday. Temperatures will be
tricky in the valleys of Southwest MT today, with a cold start,
they might not get quite as warm as currently forecasted. Brusda
&&
.AVIATION...
428 AM MST Fri Dec 2 2022 (02/12Z TAF period)
Mountain snow is expected to persist through 18z south and east of a
KDLN to KLWT line; however, little to no additional snow is expected
across the terminals of Southwest through North Central Montana.
Predominately VFR conditons are expected over the next 24 hours;
however, MVFR conditions will likely linger at times in the
northerly upslope regions through 18z to 00z Saturday, particularly
across Central and North Central Montana (i.e. KGTF, KLWT, and
KHVR). South to southwest winds will begin to increase along the
eastern slopes of the Rocky Mountain Front, Montana Hwy 200
corridor, and in the Madison Valley this afternoon and evening.
These gusty winds combined with a fresh snowpack will likely lead to
drifting and blowing snow, which could impact the KCTB, KGTF, and
KEKS terminals. Low level wind shear concerns and mountain wave
turbulence will also be on the rise over the aforementioned areas as
mid-level winds strengthen. - Moldan
Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.
&&
.PREV DISCUSSION...
/ISSUED 428 AM MST Fri Dec 2 2022/
Today through tonight...primary concern throughout the period will
be increasing winds along the eastern slopes of the Rocky Mountain
Front, Montana Hwy 200 corridor across Central Montana, and within
the Madison Valley; which in combination with a fresh snowpack will
lead to drifting and blowing snow. Additionally of concern will be
the potential for wind chill values to remain below -20 over
portions of the Hi-Line across North Central Montana through the
overnight hours tonight.
Snow was tapering off from northwest to southeast across the
Northern Rockies early this morning as transient ridging, currently
over the Pacific Northwest, was beginning to slide east towards the
Northern Rockies. Clearing skies, relatively light winds, and a
fresh snowpack over the plains of Central and North Central Montana
has allowed temperatures to plummet below zero across most locations,
with the coldest temperatures (ranging from -10 to -20) residing
along and west of the Interstate 15 corridor. Despite relatively
light (5 to 15 mph) wind speeds over the plains of Central and North
Central Montana, wind chill values have fallen between -20 and -35
across most locations. Expect these wind chill values to moderate
above Wind Chill Advisory levels through the late morning and early
afternoon today; however, areas along the US Hwy 2 corridor from Cut
Bank to Harlem may see infrequent periods in which values dip
between -20 and -30 through Saturday morning. Given that these wind
chills will not be continuous throughout the period (this afternoon
through Saturday morning), will withhold on extending the end time
of the current Wind Chill Advisory across the Hi-Line. Daytime high
temperatures across Southwest through North Central Montana are
expected to range from the teens above zero to single digits below
zero respectively. Temperatures along the eastern slopes of the
Rocky Mountain Front and Montana Hwy 200 corridor across Central
Montana will actually warm through the evening hours tonight as
southwest winds begin to increase, giving way to high temperatures
for the calendar day being reached near midnight tonight. Low
temperatures tonight are expected to range from the single digits
above/below zero across most locations, with the exception of the
Milk River Valley where the teens below zero are expected.
As previously mentioned, southerly winds will be on the increase
along the eastern slopes of the Rocky Mountain Front, Montana Hwy
200 corridor across Central Montana, and within the Madison Valley
in Southwest Montana from the afternoon and through the overnight
hours tonight. Surface pressure gradient across these areas will
begin to strengthen as high pressure builds in west/south of the
Continental Divide and an area of low pressure deepens to the east
of the Continental Divide. Additionally, H700 cross barrier flow
over Central and North Central Montana will increase to 35-55kts
during the overnight hours tonight, with any mountain wave activity
being confined to the immediate eastern slopes and High Plains
adjacent to the Rocky Mountain as temperature profiles further east
and south appear unfavorable (inversions well below ridgetops at
KCTB and KGTF) for mountain wave activity. NBM4.1 probabilistic data
suggests that wind gusts will remain below High Wind Criteria across
the CWA; however, there is a low (10-40%) probability that wind
gusts exceed 40 mph along the Montana Hwy 200 corridor, moderate (40-
70%) probability that wind gusts exceed 40 mph in the Madison
Valley, and a moderate (40-70%) probability that wind gusts exceed
45 mph along the eastern slopes of the Rocky Mountain Front. Given
the potential for mountain wave activity, a moderate (40-70%)
probability of wind gusts exceeding 45 mph, and a fresh snowpack
along the eastern slopes of the Rocky Mountain Front I have elected
to issue a Winter Weather Advisory for Blowing Snow from 19z today
through 22z Saturday. Significant reductions in visibility and
partial lane blockages can be expected in the East Glacier Park
Region, Northern High Plains adjacent to the Rocky Mountain Front,
and Southern Rocky Mountain Front where the Winter Weather Advisory
is in place. Confidence in blowing snow significantly reducing
visibilities along the Montana Hwy 200 corridor and in the Madison
Valley remains low, thus no Winter Weather Advisory was issued at
this time.
Saturday through Saturday night....temperatures will begin to
moderate into the 20s to low 30s across the Northern Rockies as
breezy southerly winds continue during the day on Saturday, with the
exception of the valleys in Southwest Montana and Milk River Valley
in North Central Montana where a strong temperature inversion will
inhibit mixing and keep temperatures in the teens. Continued
drifting and blowing of snow is expected along the the eastern
slopes of the Rocky Mountain Front, Montana Hwy 200 corridor across
Central Montana, and within the Madison Valley through Saturday
afternoon as winds gust to between 35-45 mph. Predominately dry
conditions are expected, with the exception of the Continental
Divide where an isolated snow shower is possible.
Sunday through next Friday...snow chances will begin to increase
during the day on Sunday across Southwest Montana as another surge
of Pacific moisture lifts northeast within increasingly
southwesterly flow aloft. Snow chances will spread further north and
east Sunday night across the remainder of the CWA. A cold front is
then expected to drop south and across Central and North Central
Montana on Monday, dropping temperatures back into the teens and 20s
and providing additional chances for snow through the day on
Tuesday. Drier conditions and "slightly" warmer conditions are then
expected from the middle through the end of the upcoming work week
as ridging attempts to build back in over the Northern Rockies. -
Moldan
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF 11 6 30 10 / 0 0 0 0
CTB -1 -5 18 4 / 0 0 0 0
HLN 17 -1 19 -3 / 0 0 0 0
BZN 16 -5 18 -4 / 0 0 0 0
WYS 14 -13 20 -8 / 10 20 0 10
DLN 12 -4 15 2 / 0 0 0 0
HVR -1 -11 16 2 / 0 0 0 0
LWT 9 2 31 8 / 0 0 0 0
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
...WIND CHILL ADVISORY IN EFFECT UNTIL 11 AM MST SATURDAY FOR
Eastern Glacier, Western Toole, and Central Pondera...Eastern
Toole and Liberty...Hill County...Northern Blaine County...
...Wind Chill Advisory until Noon Today for portions of North
Central MT...
...Winter Weather Advisory for blowing snow for the Rocky Mountain
Front and adjacent Plains from Noon today until 3 PM Saturday...
&&
http://www.weather.gov/greatfalls