Damaging Winds in Montana, April 5, 2024

Area Forecast Discussion
National Weather Service Great Falls MT
1107 PM MDT Thu Apr 4 2024

...Aviation Section Updated...

.SYNOPSIS...

Rain/snow continues through the weekend with temperatures slowly
cooling down. Fog and drizzle are possible Friday morning in
Central and North Central Montana, with locations along the
Northern Rocky Mountain Front can receive a light glaze of ice. A
warming trend in temperatures with drier conditions return Monday
through the middle of next week.

&&

.UPDATE...

Broad troughing across the west coast will continue to shift slowly
eastward tonight, resulting in southwesterly flow in the mid levels
and aloft across the region turning more and more southerly. As a
result, gusty southerly winds will continue across portions of
Southwest Montana, especially in north south oriented valleys. Winds
look to subside slightly overnight with reduced mixing, but increase
in magnitude again tomorrow morning.

Further north across the plains, moist northerly low level flow is
being "overrun" by a drier southerly flow aloft. The resulting
profiles suggest fog, drizzle, and freezing drizzle (Where surface
temperatures are cool enough) will be a concern overnight into
Friday. Additionally, precipitation looks to continue across
northern portions of the high plains and Rocky Mountain Front
overnight. A mix of rain and snow looks likely on the plains, with
snow being the primary precipitation type adjacent to the Rocky
Mountain Front and in the mountains. The banded nature of
precipitation in this area will result in heavy snow at times
through around midnight. The going Winter Weather Advisory is in
good shape for this area, which will go through 6 AM Friday. All
in all, just some small tweaks were made to the forecast this
evening to adjust toward current trends and to incorporate the
latest guidance. -AM

&&

.AVIATION...

1107 PM MDT Thu Apr 4 2024 (05/00Z TAF Period)

Low stratus and periods of drizzle, mist, or rain/snow will continue
to bring LIFR/IFR conditions to the plains of North Central and
Central Montana and even the valleys of Central Montana along and
north of the US Hwy 12 corridor through at least 15-18z Friday.
Beyond 15-18z Friday the latest HREF (Hi-Res Ensemble Forecast)
guidance suggest that MVFR conditions will return to the KHVR, KLWT,
and KHLN terminals; however, LIFR/IFR conditions are favored (40-60%
chance of CIGS less than 1000ft) to persist at the KCTB and KGTF
terminals through the remainder of the TAF period. Further south, VFR
conditions are expected through 18z Friday at the KBZN and KEKS
terminals before increasing low to mid-level cloudiness brings
MVFR/low-VFR conditions. Additionally, precipitation chances will
be on the increase beyond 18z Friday across all terminals, with even
a few embedded thunderstorms potentially impacting the KHLN, KBZN,
and KEKS terminals through 03z Saturday. Primary threat from any
thunderstorms Friday afternoon and early evening would be gusty and
erratic winds and lightning. Mountains will be obscured north of
the I-90 corridor through the next 24 hours, with increasing
obscuration south of this line beyond 18z Friday. - Moldan

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

&&

.HYDROLOGY...

A flood warning has been issued for Lodge Creek, in northern
Hill/Blaine counties. The latest forecast has the creek rising above
moderate flood stage by this weekend. How heavy of rainfall and how
much snowmelt occurs over the Cypress Hills in southern Canada over
the next day or so will have some impact on how high the creek
rises. Additionally, do expect the Milk River to rise as well
through this weekend, but at this time the Milk River should remain
below flood stage. Brusda

&&

.PREV DISCUSSION...
/ISSUED 516 PM MDT Thu Apr 4 2024/

The Rest of the Day...An upper level shortwave will continue to
spark precipitation over the Continental Divide, Central, and
North Central MT through tonight. Some clearing in the morning
clouds across Southwest and Central MT has allowed some weak
instability to build in. This combined with modest wind shear
profiles do support the small chance of a few isolated
thunderstorms this afternoon. SPC has kept a localized area just
southwest of Great Falls to Missoula/Butte in a marginal risk for
severe weather. The overall severe threat remains low, however I
can't rule out an isolated storm with heavier wind gusts/small
hail. Increased winds aloft in Southwest MT this afternoon will
create gusty winds in Beaverhead and Madison counties. Model
guidance still supports these winds overall stay below high wind
criteria. The Winter Weather Advisory for the Northern Rocky
Mountain Front remains in effect through early Friday morning, as
this upper level shortwave will bring in additional snowfall
tonight. Lower elevations can see up to a few inches, with an
additional 4-8" possible in the mountains.

Friday Morning...Low level moisture from today's precipitation
lingers into the morning hours Friday. This combined with some low
level ascent from the surface low pressure and surface trough
will create some drizzle/fog across Central/North Central MT and
the Rocky Mountain Front. Places along the Rocky Mountain Front
(mainly west of I-15) where temperatures drop below freezing
Friday morning have a chance to accumulate a light glaze of ice
from freezing drizzle. Anyone traveling in that region should
prepare for icy road conditions.

Friday Night Through Sunday...There still lies some uncertainty
for this next storm system coming in this weekend. There are two
separate pieces in this system. The first piece arrives along the
surface boundary Friday evening through Saturday. Another small
upper level trough moves into the area Sunday, keeping the
precipitation around until Monday. As of right now, the rain and
snow line looks to set up across the lower elevations.
Precipitation looks to be a mix of rain and snow. That is where
the main uncertainty lies for the lower elevations. Overnight
temperatures look to be right around/below freezing across the
lower elevations Saturday and Sunday morning. Surface temperatures
slightly increase throughout the afternoon. This creates some
uncertainty into how much snow accumulates and sticks to the
ground. Snow totals have been fluctuating over this 48 hour period
as there is a few scenarios that can happen. Snow falling during
the overnight/morning hours can melt throughout the afternoon
hours with the warmer temperatures, leading to low snow
accumulations. On the other hand, enough dynamic cooling from the
snowfall can help keep temperatures cooler, helping snow
accumulate more which leads to higher totals.

For higher elevations, probabilistic guidance shows the Little
Belts, the Gallatin Range, and the Big Snowy Mountains having a 50-
70% chance of exceeding 8" of snow. Model guidance suggests the
chances of some locally heaver snowfall bands setting up along the
Big Snowy Mountains and the Lewistown Divide. Therefore, a Winter
Weather Watch has been issued for the Snowy and Judith Mountains
from late Friday night through Sunday evening. The main impacts with
this system will be heavy wet snow accumulating on power lines,
causing some power outages. Travel over mountain passes will also be
difficult. I expect additional winter highlights for this event will
be issued in future shifts, but this Winter Weather Watch highlights
the corridor for where the heaviest snowfall will occur at this
time. -Wilson

Monday through next Thursday...On Monday the system has mostly moved
out of the area and weak upper-level flow remains before an upper-
level ridge begins to move towards Montana. By noon on Monday all
precipitation will most likely have moved out of the area.
Temperatures will begin to warm up on Monday and skies begin to
clear out. On Tuesday clusters indicate that an upper-level ridge
begins to move over North-central, Central, and Southwestern
Montana. This will begin to warm temperatures up across most areas.
On Wednesday clusters indicate that the upper-level ridge begins to
move east. This will clear skies and allow for high temperatures to
warm even more. On next Thursday clusters indicate that the upper-
level ridge will stay over North-central, Central, and Southwestern
Montana. Clear skies and warm temperatures will be in place on
Thursday. -IG

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  35  45  33  39 /  50  50  90  70
CTB  30  39  29  38 /  90  30  80  50
HLN  35  56  34  45 /  20  70  80  70
BZN  36  63  31  44 /  10  70  70  70
WYS  29  52  21  37 /  20  80  70  80
DLN  37  57  30  44 /  10  60  50  60
HVR  33  56  33  42 /  30  20  60  70
LWT  35  58  30  37 /  20  20  70  80

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 AM MDT Friday for East Glacier
Park Region-Northern High Plains.

Winter Storm Watch from late Friday night through Sunday evening
for Snowy and Judith Mountains.

&&

http://www.weather.gov/greatfalls