980
FXUS65 KTFX 210229
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
829 PM MDT Mon May 20 2024

.UPDATE...

Showers and isolated thunderstorms are decreasing in coverage and
intensity this evening as the atmosphere stabilizes. A few
snow showers may linger later into the overnight period across the
mountains of Madison and Gallatin counties with some additional
shower activity also moving across areas near the Canadian
border. Some fog development is possible overnight, particularly
across north-central MT where dewpoints are in the mid 30s but
also in the West Yellowstone area where a period of snow occurred
this evening. Hoenisch

&&

.SYNOPSIS...

This afternoon and evening and Tuesday afternoon and
evening there will be scattered showers with some rumbles of
thunder. Tuesday morning there will be isolated areas of fog
along the Hi-Line. Wednesday through Thursday a new upper-level
system will bring widespread precipitation to the area. Friday
will be calm before a new system moves into the area for Memorial
Day Weekend.

&&

.AVIATION...
21/00Z TAF Period

Showers and isolated thunderstorms will continue to decrease in
coverage through the rest of this evening with a few showers
lingering across the mountains of southwest MT and areas near the
Canadian border through the overnight period. Areas of mountain
obscuration and very brief MVFR remain possible near showers
through the rest of this evening with some potential for patchy
fog development across portions of north-central MT and in the
KWYS vicinity later tonight. Hoenisch

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

&&

.HYDROLOGY...
A flood watch remains in effect for the Kings Hill, Monarch and
Neihart areas from Wednesday night into Friday. There is a 60
percent chance of 1 inch of liquid from this event in this area.
There is a 20 percent chance of 2 inches of liquid. This is a small
increase from yesterday. Some of the precipitation will fall as
snow, especially for elevations above 7000 feet, which will help,
but for areas lower than 7000 feet, impacts could develop fairly
quickly given how saturated the soil is and how full the
creeks/streams are currently in this region.

Some forecast models still prog near 2 inches of QPF on the higher
side. The probability of that occurring outside the Kings Hill area
is less than 10 percent. However, it would be falling in less than
24 hours. Thus some minor flood impacts could develop elsewhere over
Central MT should the higher rainfall amounts pan out. Until we have
more confidence in these higher rainfall amounts, no additional
flood highlights are planned for at this time. Brusda

&&

.PREV DISCUSSION...
/ISSUED 226 PM MDT Mon May 20 2024/

This afternoon through Tuesday... This afternoon and evening there
will be isolated rain showers with a few rumbles of thunder across
North-central, Central, and Southwestern Montana due to an upper-
level trough that is moving through the area. Due to cold
temperatures aloft there is the potential for small (up to half
an inch) hail with the thunder this afternoon and evening. Tuesday
morning isolated areas of fog will form along the Hi-Line. On
Tuesday there will be another upper-level disturbance that will
produce isolated rain showers with a few rumbles of thunder
primarily across the eastern portion of North-central, Central,
and Southwestern Montana during the afternoon and evening.

Wednesday through Thursday... On Wednesday a strong upper-level
trough begins to move over North-central, Central, and Southwestern
Montana. This trough progresses eastward across the area Wednesday
and Thursday and exits by 12 AM Friday. This will produce widespread
precipitation across North-central, Central, and Southwestern
Montana beginning Wednesday afternoon and continuing through 12 AM
Friday. For the mountains of Southwestern and South-central Montana
and the Southern Rocky Mountain Front there is a 50 - 70% chance for
8 inches or more snowfall. As a result a Winter Storm Watch remains
in effect/is in effect for all of those areas. See the
WATCHES/WARNINGS/ADVISORIES section below for details. This snow
will be heavy and wet and could cause broken tree limbs. For this
system there is a 40 - 60% chance of locations across Central
Montana receiving an inch or more rain. For the lower-elevations
of Southwestern Montana and North-central Montana there is a 30 -
50% chance for receiving a half inch of rain or more. See the
HYDROLOGY section below for more information. Continue to monitor
the forecast for details.

Friday through next Monday... On Friday there will be zonal flow
above North-central, Central, and Southwestern Montana. On Friday
there is a 50% chance for locations along the Northern Rocky
Mountain Front having wind gusts greater than 47 mph due to a strong
surface pressure gradient. On Friday it will be dry across North-
central, Central, and Southwestern Montana. On Saturday and
Sunday clusters have a trough over North-central, Central, and
Southwestern Montana. The trough strength and timing varies
between clusters. This indicates that unsettled, cool, and rainy
weather will likely continue for the Saturday and Sunday of
Memorial Day Weekend. Next Monday (Memorial Day) clusters begin
to diverge. This will need to be monitored for updates. -IG

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  35  63  42  60 /  30  30  10  70
CTB  34  61  39  56 /  40  30  10  70
HLN  39  66  44  62 /  20  30  10  80
BZN  32  61  37  60 /  30  40  10  70
WYS  28  53  30  49 /  60  50  10  70
DLN  30  59  39  57 /  30  20  10  80
HVR  38  63  40  64 /  50  30  20  50
LWT  32  58  37  60 /  20  50  20  60

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Wednesday evening through Thursday
morning for Elkhorn and Boulder Mountains-Northwest Beaverhead
County-Ruby Mountains and Southern Beaverhead Mountains-Southern
Rocky Mountain Front.

Flood Watch from Wednesday evening through Friday morning for
Little Belt and Highwood Mountains.

Winter Storm Watch from Wednesday evening through Thursday
afternoon for Big Belt, Bridger and Castle Mountains-Gallatin
and Madison County Mountains and Centennial Mountains.

&&

$$

http://www.weather.gov/greatfalls