514
FXUS65 KTFX 290149
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
749 PM MDT Sun Apr 28 2024


.SYNOPSIS...

A slow moving and strong upper level disturbance will bring
unsettled conditions to the Northern Rockies through the middle of
the upcoming work week, with accumulating snow becoming more
likely along the Rocky Mountain Front and across the Island Ranges
of Central Montana from Tuesday evening through Wednesday.

&&

.UPDATE...

Latest satellite imagery continues to show high level clouds
along the Northern Rocky Mountian Front and across North Central
Montana this evening. Current temperatures and winds are doing
well in the forecast. No changes were needed this evening to the
current forecast. Gusty westerly winds continue to diminish this
evening with the exception of the Rocky Mountain Front, but
returns for tomorrow afternoon and includes locations across
Southwest Montana. Webb

&&

.AVIATION...
540 PM MDT Sun Apr 28 2024 (29/00Z TAF Period)

VFR conditions continue through this evening, with rain showers
moving into Southwest and Central Montana airfields tomorrow morning
into the afternoon hours, bringing MVFR to low VFR conditions.
Mountain wave activity continues through the TAF period for the
Rocky Mountain Front. Gusty westerly winds should diminish through
the overnight hours, but return tomorrow afternoon across North
Central Montana as well as Southwest Montana airfields. Webb

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

&&

.PREV DISCUSSION...
/ISSUED 540 PM MDT Sun Apr 28 2024/

Rest of today through Tuesday...satellite imagery shows an
unseasonably deep trough in the Gulf of AK with upper level jet to
its south approaching the west coast. Flow splits downstream with a
weaker shortwave lifting out across MT while the rest of the energy
tracks across the SW US into an upper level system lifting out into
the central US plains. Enough residual moisture in the flow and weak
instability will help to maintain some isolated to widely scattered
showers across the mountains of western and southwest MT through
this evening.

The incoming upper jet and initial shortwave moving out of the Gulf
of AK trough reach the Northern Rockies Monday with a cold front
shifting east across most of the area by Monday evening. Larger
scale ascent and some modest instability should support a fairly
widespread coverage of showers and a few thunderstorms Monday
afternoon across areas roughly along and southeast of a line from
Lincoln to Great Falls and Havre. Precipitation amounts of 0.25" or
more are most likely (50-70% probability) across eastern portions of
central/SW MT (Judith Basin, Fergus, Meagher and Gallatin counties)
where probabilities for thunderstorms are also around 50-70%. These
areas could also see some stronger wind gusts (35-45 mph) with any
storms that develop due to the more favorably timed late afternoon
frontal passage. Gusty west to northwest winds spread across most of
the area behind the front Monday night and continue through Tuesday
as surface low pressure develops in southern Saskatchewan to the
north of a mid level circulation tracking east along the
international border. - Hoenisch

Tuesday night through Wednesday night...is shaping up to be the most
impactful stretch across Southwest through North Central Montana,
most notably along the eastern slopes of the Rocky Mountain Front
and Island Ranges of Central Montana, as a strong shortwave trough
and associated closed low slowly pivots east over Northern Montana
and Southern Saskatchewan. This upper level disturbance will help to
pivot precipitation westward towards the Continental Divide through
the evening hours on Tuesday, with precipitation then spreading
south towards Central Montana through Wednesday morning and
persisting here through Wednesday evening. NBM probabilities for 6"
of snow throughout the period across the East Glacier Park Region
generally ranges from 40-60%, with areas along and north of a Two
Medicine to Hudson Bay Divide line having the highest probabilities.
With increasing recreation and subsequent travel on routes adjacent
to Glacier National Park, most notably US Hwy 89 north of Browning,
have decided to issue a Winter Storm Watch for the East Glacier Park
Region given the potential impacts to those unprepared for a return
to winter like conditions. Additionally, as the precipitation shifts
southeastward towards the Montana Hwy 200 corridor through Wednesday
morning, latest NBM probabilities support a 40-60% chance for
snowfall accumulations to reach 8" across the Little Belt Mountains.
Have held off for now on a Winter Storm Watch, but should trends
continue then one will need to be considered given the impacts to
travel on US Hwy 89.

Thursday through next weekend...Ensemble cluster largely favor
unsettled northwest to northerly flow over the Northern Rockies,
which will help to maintain chances for precipitation and
temperatures near or slightly below normal. - Moldan

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  40  55  37  53 /  20  70  50  20
CTB  38  58  33  47 /  20  10  20  40
HLN  42  52  35  54 /  30  90  40  30
BZN  37  57  24  47 /  40  90  80  30
WYS  28  48  19  40 /  40  90  80  50
DLN  34  55  24  47 /  10  80  50  30
HVR  38  64  38  54 /   0  30  40  40
LWT  39  55  31  49 /  20  90 100  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Tuesday evening through Wednesday
morning for East Glacier Park Region.

&&

$$

http://www.weather.gov/greatfalls