317
FXUS65 KTFX 070207
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
810 PM MDT Mon May 6 2024

.SYNOPSIS...

A dynamic and impactful weather system will impact North Central
and Southwestern Montana through midweek with mostly rain at
lower elevations and snow in the mountains, along with strong,
gusty winds across the Plains and north/south oriented valleys of
Southwestern Montana. Travel over passes will be difficult at
times, especially through the Little Belts where blizzard
conditions are possible. After an active first half of the week,
warmer and drier weather is expected for the end of the week.

&&

.UPDATE...

Inherited forecast is performing nicely; therefore, no update is
necessary, at this time.
- Fogleman

&&

.DISCUSSION...

Key Points:

-Highly impactful spring storm to impact the area through the
middle of this week, bringing gusty winds to most of the area,
heavy snow to the Central Montana Mountains, and soaking rainfall
to the plains

-Most areas across the plains have a >50% chance of seeing at
least 1 inch of rainfall and rain equivalent through Thursday
morning, with areas east of a line from Havre to Great Falls to
Lewistown having a >50% chance of seeing at least 2 inches of
precipitation

-Blizzard conditions are expected in the Little Belt Mountains,
with heavy snow and wind combining to produce near zero visibility
at times, especially Tuesday night and into Wednesday morning.
For accumulations, all mountain ranges across North Central
Montana have areas where the probability of a foot of snow is
greater than 50% through Thursday morning, with the higher
elevations of the Little Belt and Snowy Mountains seeing a >80%
chance of over two feet.

-Southwestern Montana will see damp and breezy conditions at
times, though generally not as impactful as what will be found
across the plains

-Warmer and drier weather returns towards the end of the week

Short term (Through Wednesday)... Clouds continue to thicken
today as a strengthening surface low pressure system in Eastern
Wyoming continues to move to the north today. As this low
continues to deepen and move northward, moisture from the Pacific
and Gulf of Mexico will continue to wrap around this system, and
will deposit as periods of moderate to heavy rain across the
plains, with snow in the higher terrain, especially in the Little
Belt and Snowy Mountains.

For today, expect winds to continue to increase across the
plains, as rain continues to increase in intensity and coverage,
especially east of a Cut Bank to Great Falls to White Sulphur
Springs line. The steadiest and most intense rain will generally
be east of a Lewistown to Havre line, where steady precipitation
will result in most of this area seeing a quarter inch or more
through midnight tonight (50% or higher chance). Across the rest
of the area, expect winds to continue to increase across the
plains and into the Southwest valleys as clouds continue to push
into the area.

Tuesday will see wind and rain continue to overspread the plains
as the low over Eastern Montana and the Dakotas stalls and
continues to deepen. With this low to our east, moisture will
continue to stream into the area from the east, pulling moisture
in from the Gulf of Mexico. This moisture will begin to focus in
on North Central Montana through the day on Tuesday as
northeasterly flow at the surface and aloft result in upslope
precipitation, not only in the mountains, but also across the
plains as moisture moves up the Missouri River Basin. In addition
to the heavy rain, we will continue to see strong winds across the
plains and North South oriented valleys as cyclonic flow around
the low couples with an increasingly strong pressure gradient
across the state. Turning our attention to the higher elevations,
This combination of wind, along with precipitation falling as
snowfall, will create some very poor visibility, especially in the
Little Belt Mountains, where the Winter Storm Warning has been
upgraded to a Blizzard Warning, as the combination of heavy
falling snow and frequent wind gusts over 35 mph will result in
very poor to near zero visibility for much of day on Tuesday,
especially from mid morning on, especially between Sluice Boxes
State Park and Monarch Canyon, and from Kings Hill Pass to Jumping
Creek Campground. If you find yourself in a situation where you
must travel and you do get stuck, be prepared for increased
response times. In addition to the travel impacts, the heavy and
wet nature of the snow may cause abnormal stress on trees and
power lines, which could result in some power outages, and
livestock in these areas may struggle to maneuver through the deep
and dense snow.

Some modest improvement is expected in the weather on Wednesday
as our weather system begins to slowly weaken and begins to slowly
move to the east, but the precipitation will continue across the
plains and even begin to push into Southwest Montana. At the same
time, we will need to watch snow levels closely for Wednesday
morning as colder air works its way in from the north, which may
result in some snow reaching the plains on the northern slopes of
the Little Belt and Snowy Mountains, including the US 89 corridor
from Great Falls to Lewistown. While any accumulations of snow
will be limited, we will have the potential for some slushy
accumulations, and in the unlikely event that we do see rain
change to snow earlier, we could see some tree damage, especially
to any trees that have already begun to leaf out. Looking to the
southwest, expect periods of snow and some valley rain through the
day on Wednesday, though any snow should struggle to accumulate
at lower elevations and even on roads through the passes as the
May sun angle and latent heat in the ground should be able to help
keep roads from seeing much in the way of accumulation.
Precipitation will begin to taper off Wednesday night as our
system begins to get further east, with mostly light precipitation
and decreasing winds overnight Wednesday night. Ludwig


Extended (Thursday thru next Monday)...snow will continue to
decrease in areal extent and intensity through the day on Thursday
across the Northern Rockies, with snow lingering the longest over
the Central Montana mountains through the early evening hours on
Thursday. Broad upper level riding over the Eastern Pacific and
western seaboard through the end of the work week will attempt to
build east towards the North Rockies through the weekend; however,
ensemble clusters predominately keep the ridge axis west of the
Continental Divide, with Southwest through North Central Montana
remaining below northwesterly flow aloft. This northwesterly flow
aloft will help to maintain isolated to scattered showers across
much of the CWA over the weekend, most notably along and north of
the US Hwy 12 corridor. Temperatures will gradually warm through
the end of the work week to near normal, with temperatures warming
above normal over the weekend as the aforementioned ridge moves
closer to the Northern Rockies and the low level flow backs to the
southwest (i.e. weak downsloping surface winds). - Moldan

&&

.AVIATION...
656 PM MDT Mon May 6 2024 (07/00Z TAF Period)

Note: The NWS Great Falls Weather Forecast Office manages the
following TAFs: KCTB, KHVR, KGTF, KLWT, KHLN, KBZN, KEKS and KWYS.

During this 07/00Z TAF period, precipitation becomes widespread,
causing conditions at KEKS and KWYS to slip into the MVFR/IFR range
from 07/10Z. All other airfields are forecast to degrade into MVFR
conditions beginning with our north and east most airfields,
followed by the remaining airfields as precipitation and low ceiling
expands across the region in a southwestward direction. Degraded
airfield conditions are forecast to occur due to rain/snow and mist
or blowing snow, and with low ceiling. Mountain obscuration should
be expected. Widespread strong westerly to northwesterly gusty winds
are forecast. High Wind Warnings are in effect for most of north
central and central Montana, for the duration of this TAF period.
Mountain wave turbulence is forecast.
- Fogleman

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

&&

.HYDROLOGY...

A slow moving Pacific weather system will bring an extended
period of lower elevation rain and mountain snow this week, with
the heaviest precipitation falling Tuesday through early
Thursday. NBM probabilistic guidance highlights the eastern
portions of Central/North-central MT with the heaviest rainfall
amounts for this period, largely supporting 1 to 3 inches of
rainfall/snow melt liquid equivalent over locations east of a
Great Falls to Shelby line Tuesday through Thursday.

While flooding is generally not expected, some rivers, creeks,
and streams along the Canadian border in Hill and Blaine Counties
are expected to approach or reach action stage Wednesday and
Thursday, mainly impacting unpopulated rural locations. Anyone
near waterways should remain alert for changing conditions and be
prepared to seek higher ground should water rises occur. - RCG

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  39  46  34  43 /  20 100 100 100
CTB  37  45  33  44 /  20 100 100 100
HLN  38  49  37  46 /  10  60 100 100
BZN  33  49  32  45 /  10  50 100 100
WYS  26  41  27  44 /  30  60  90  80
DLN  30  46  33  47 /  10  20  80  80
HVR  41  48  38  56 / 100 100 100  90
LWT  34  39  31  39 /  60 100 100 100

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 6 AM MDT Wednesday for Bears Paw
Mountains and Southern Blaine-Eastern Toole and Liberty-Fergus
County below 4500ft-Hill County-Judith Basin County and Judith
Gap-Northern Blaine County-Snowy and Judith Mountains-Western
and Central Chouteau County.

Winter Weather Advisory from 3 AM Tuesday to 6 AM MDT Wednesday
for Bears Paw Mountains and Southern Blaine-Eastern Toole and
Liberty.

Winter Storm Warning from noon Tuesday to midnight MDT Wednesday
night for Big Belt, Bridger and Castle Mountains-East Glacier
Park Region-Snowy and Judith Mountains-Southern Rocky Mountain
Front.

High Wind Warning until midnight MDT Tuesday night for Big Belt,
Bridger and Castle Mountains-Canyon Ferry Area-Elkhorn and
Boulder Mountains-Gates of the Mountains-Helena Valley-Meagher
County Valleys-Upper Blackfoot and MacDonald Pass.

Blizzard Warning from noon Tuesday to midnight MDT Wednesday
night for Little Belt and Highwood Mountains.

Winter Weather Advisory from 6 PM Tuesday to midnight MDT
Wednesday night for Elkhorn and Boulder Mountains-Gallatin and
Madison County Mountains and Centennial Mountains-Upper
Blackfoot and MacDonald Pass.

Winter Weather Advisory from 6 AM Tuesday to noon MDT Wednesday
for Cascade County below 5000ft-Fergus County below 4500ft-
Judith Basin County and Judith Gap.

High Wind Warning until 6 PM MDT Tuesday for East Glacier Park
Region-Eastern Glacier, Western Toole, and Central Pondera-
Northern High Plains-Southern High Plains-Southern Rocky
Mountain Front.

High Wind Warning until noon MDT Tuesday for Little Belt and
Highwood Mountains.

&&

$$

http://www.weather.gov/greatfalls