420
FXUS65 KTFX 050634
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1235 AM MDT Sun May 5 2024

UPDATED AVIATION SECTION

.SYNOPSIS...

After a seasonable and dry day today, an active weather pattern is
expected through the middle of next week. Expect widespread
soaking rain and winds across the plains, with significant
snowfall across some of the mountain ranges, especially the Little
Belt Mountains. Next week will end on a warmer and drier note as
high pressure builds back into the area.

&&

.UPDATE...

The forecast is performing sufficiently well; therefore, no updates
are made, at this time.
- Fogleman

&&

.DISCUSSION...

Key Points:

-Seasonable this weekend with a few showers in SW Montana on
Sunday

-Significant spring system affects the area early next week,
bringing widespread soaking rain and heavy mountain snow, along
with widespread gusty winds

-Warmer and drier weather will return later next week

Short term (Through Sunday)...Satellite and radar this morning
and early afternoon have shown mostly clear skies across the area
today as high pressure to the east has helped to result in a
tranquil day across North Central and Southwestern Montana.
However, the signs of a change in weather pattern are beginning to
make their appearance across the area, as clouds have begun to
push in from the Southwest. For today, these clouds will not do
much other than filter out some sunlight as temperatures reach the
upper 50s and 60s today across the lower elevations and into the
upper 40s and 50s in the higher terrain. An upper level low will
push into the Great Basin overnight tonight and through the day on
Sunday, which will bring a further increase in cloud cover and
some rain to mostly Southwestern Montana for the day on Sunday.
This first round of precipitation will generally be on the light
side, with most locations seeing a tenth of an inch of less
through the day on Sunday, with some higher amounts possible along
the MT/ID border. With that said, precipitation will increase in
coverage and intensity Sunday night as a surface low pressure
system moves northward out of Utah and Wyoming into Eastern
Montana Sunday evening, which will allow for some more widespread
moderate to heavy rain to set up across a decent portion of North
Central and Southwestern Montana.

Extended (Monday through next Saturday)... Our weather system
will continue to strengthen as we head into the work week as an
upper level low ejects out of the Great Basin and moves towards
North Dakota before stalling out and linking with an existing
trough over the Pacific Northwest. For Monday, this will result in
cloudy, cool, and breezy conditions across the plains, with
breezy with snow showers across the Southwest as moisture from the
Pacific streams into the area. Rain will push into North Central
Montana from the north Monday night and Tuesday as the main
surface low retrogrades back to the east, and will be widespread
and heavy Tuesday and Wednesday. Rainfall will likely be heaviest
along and east of a Great Falls to Shelby line across the plains,
with rain amounts trailing off as you get south of the Little
Belt and Snowy Mountains and west of the aforementioned line. In
this area, NBM 50th percentile values generally exceed 1.5 in the
72 hours between Monday night and Thursday morning, with the 75th
percentile values exceeding 2. While heavy rain and associated
ponding/low lying flooding will be the most widespread concern
through the next week, we will also be dealing with heavy, wet
snow across the mountains, particularly the Big and Little Belts
and the Snowy Mountains. Current probabilities for snowfall in the
Monday night-Thursday morning time frame show a 75% chance of
seeing 30 of snow (roughly 10 per day) with this system, with
the Big Belts seeing a 75% chance of at least 8 of snow. In
addition to the heavy rain and snow, the deepening and
retrograding low pressure system at the surface will help generate
some strong and sustained winds across the plains, with multiple
areas seeing prolonged periods of a >50% chance of 50 mph gusts,
mostly along the Rocky Mountain Front and east of a Great Falls to
Havre line. This wind, combined with the rain and snow, could
amplify impacts, especially where saturated soils make trees more
likely to be uprooted.

This system will begin to wind down Thursday, with ensembles
showing fairly high agreement of high pressure beginning to build
into the area for the end of the week. With this high pressure
building in, expect warmer and drier weather for the end of the
week. Ludwig

&&

.AVIATION...
1235 AM MDT Sun May 5 2024 (05/06Z TAF Period)

Note: Amendments are not scheduled for KEKS until their observation
can be fully returned to service. An estimated time for return to
service is not known at this time. Thank you for your patience.

VFR conditions are expected to continue through at least 06/06Z for
most of North Central (KCTB KHVR), Central (KLWT KGTF KHLN) and
Southwest (KBZN KEKS KWYS) Montana, unless otherwise specified.

A moderate southerly flow aloft with south to east winds gusting to
35 kt at times at the surface will cause periods of low level wind
shear through around 15Z. Moisture in the flow aloft will spread
high- and mid-level cloudiness north over the area through the
period, with the best chance for persistent mountain-obscuring MVFR
ceilings occurring at KWYS with an increase in precipitation.
Otherwise, scattered rain showers and high mountain snow showers are
forecast to spread north over the area more so after 12Z, with snow
levels lowering over Southwest Montana after 00Z. A few
thunderstorms may also develop over Southwest Montana after 18Z,
possibly moving into Central Montana after 22Z or so; however,
confidence is low at this time that thunderstorms will directly
impact most terminals (except for possibly KWYS), so have mostly
left mention out of TAFs. Main threats from these storms will be
isolated lightning strikes and brief heavier periods of rain
possibly causing MVFR conditions, but erratic wind gusts and small
hail cannot be ruled out.

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  43  63  43  54 /  10  30  70  50
CTB  37  60  40  53 /   0  30  30  40
HLN  44  69  43  54 /  10  60  90  60
BZN  42  66  36  51 /  10  70  90  80
WYS  36  53  28  42 /  30  90  90 100
DLN  44  60  35  49 /  20  70  90  60
HVR  39  71  44  56 /   0  10  60  70
LWT  36  65  38  48 /   0  20  80  70

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Tuesday morning through Thursday morning
for Big Belt, Bridger and Castle Mountains-Little Belt and
Highwood Mountains-Snowy and Judith Mountains.

&&

$$

http://www.weather.gov/greatfalls