373
FXUS65 KTFX 231554
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
954 AM MDT Thu May 23 2024

.SYNOPSIS...

Precipitation that has prompted Winter Storm Warnings and Winter
Weather Advisories will end from northwest to southeast through the
day today. Additional showers and a few thunderstorms look to
develop across primarily North-central Montana this afternoon.
Unsettled weather lasts into the weekend before a warming and drying
trend starts late Sunday into early next week.

&&

.Update...

Morning update has been published, with no major changes made to
the on-going forecast. Widespread precipitation, which was
associated with an upper level disturbance moving over Northwest
Wyoming, was slowly decreasing in areal coverage from the north
and west across Central and Southwest Montana. This trend is
expected to continue through the early afternoon hours across
these areas, with most if not all of the precipitation pulling
away prior to 3 PM MDT. The one exception will be across eastern
portions of Southwest Montana where northerly upslope flow will
help to maintain rain and snow showers across the Gallatin,
Madison, and Bridger Ranges and surrounding foothills through the
early evening hours tonight. Additionally, clearing skies across
North Central Montana this morning will allow the boundary layer
to warm, which combined with moist and cool northwesterly flow
aloft will lead to increasing instability. This instability
combined with embedded waves diving southeast within the
northwesterly flow aloft will help to promote the development of
showers and thunderstorms over North Central and northern portions
of Central Montana by the early afternoon, with these
showers/storms persisting through the overnight hours. - Moldan

&&

.AVIATION...
23/06Z TAF Period

A mix of rain and snow across Southwest through Central Montana will
slowly decrease in areal extent and eventually diminish late morning
or early afternoon. Expect mountain obscuration through the morning
across most areas. Showers and a few thunderstorms look to develop
across western portions of North-central Montana early this
afternoon, with limited confidence that a thunderstorms impacts any
TAF sites. Fog will be a concern late tonight where clearing skies
overlap with areas that will see precipitation today. -AM

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

&&

.HYDROLOGY...

A Flood Watch remains in effect for areas near creeks and streams
over in the Little Belt Little mountains through Friday morning.
Current probabilistic forecasts support one to two inches of
rainfall/liquid equivalent precipitation through Friday.
Snow levels will fluctuate with this weather system. However, there
are concerns for flooding on area creeks and streams given recent
precipitation/saturated soils and at least a portion of the upcoming
precipitation falling as rain at all elevations. Those near water
should be vigilant and ready to seek higher ground if flooding
occurs.

&&

.PREV DISCUSSION...
/ISSUED 506 AM MDT Thu May 23 2024/

Through tonight...The upper level disturbance that has been
advertised the past several days has finally made its appearance,
currently across southern ID. Cool temperatures aloft resulted in
numerous showers and a few thunderstorms late yesterday that
eventually resulted in a congealed stratiform rain across the
plains, which is now stretching southwestward across the Continental
Divide (With snow falling in the mountains). High resolution
guidance drifts this area of precipitation southeastward through the
remainder of the night as the responsible upper level disturbance
and associated forcing also shifts in that direction. Meanwhile a
somewhat narrow corridor of H7-H6 frontogenesis will develop across
Southwest Montana this morning north/northwest of an easily
identifiable upper level low presently near Monida, resulting in
another band of precipitation. The two bands eventually
consolidate across Central and Southwest Montana this morning
before shifting southeastward and dissipating late this morning
and into the afternoon.

Snow levels are generally around 5500ft as of ~230 AM, and will
continue to fall through around mid morning. Lower elevation snow
continues to looks likely at times in Southwest Montana valleys
through the late morning or early afternoon once precipitation
diminishes or moves away from the region. Consideration was given
toward an upgrade to the lower elevation Winter Weather Advisory in
the Bozeman area. The concern is for higher amounts on the far south
side of the Gallatin Valley where snow looks to begin a bit earlier
than the remainder of the Gallatin Valley. Localized snow amounts on
the order of 6 inches or so would not surprise me in this area.
Given the limited areas extent of these higher snowfall amounts, I
elected to stick with the going Winter Weather Advisory.

Meanwhile further north, partly cloudy skies across the northern
plains late morning will combine with cool air aloft to result in
showers and a few thunderstorms this afternoon and evening. An upper
level disturbance across South-central Canada will retrograde back
west a bit, with a wave pivoting around its western periphery
tonight in the vicinity of North-central Montana. This will allow
for scattered showers to continue into the overnight in this area.

Friday through Sunday morning... The northern Rockies will be
between systems on Friday, though cool northwesterly flow aloft will
promote late morning through early evening showers and
thunderstorms. Another system this weekend looks to take a similar
track as the last system (Drop south from BC, shift east across
southern ID, finally exiting eastward across WY), but this system
has trended to be less organized in nature compared to the first.
Hence, an unsettled periods still looks likely Saturday afternoon
into Sunday morning, with confidence in more widespread impacts
decreasing at this time.

Sunday afternoon into the middle of next week... Ensembles favor
a return to upper level ridging late Sunday into early next week.
A warming trend looks likely, with limited chances for an
afternoon shower or thunderstorm. There is uncertainty how long
the ridging lasts, as most ensemble members bring an upper level
disturbance and Pacific cold front across the region mid week at
some point. -AM

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  53  39  63  39 /  70  20  30  20
CTB  53  39  61  37 /  60  70  40  20
HLN  54  37  66  42 / 100  10  20  20
BZN  48  26  62  36 / 100  10  20  20
WYS  41  23  55  29 / 100  20  20  20
DLN  48  27  61  36 / 100  10  20  20
HVR  55  42  63  40 /  30  60  60  20
LWT  47  33  59  36 /  90  20  40  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...

Winter Storm Warning until noon MDT today for Elkhorn and
Boulder Mountains-Northwest Beaverhead County-Ruby Mountains and
Southern Beaverhead Mountains-Southern Rocky Mountain Front-
Upper Blackfoot and MacDonald Pass.

Winter Weather Advisory until noon MDT today for Gates of the
Mountains.

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

Winter Storm Warning until 6 PM MDT this evening for Big Belt,
Bridger and Castle Mountains-Gallatin and Madison County
Mountains and Centennial Mountains-Little Belt and Highwood
Mountains-Snowy and Judith Mountains.

Winter Weather Advisory until 3 PM MDT this afternoon for
Beaverhead and Western Madison below 6000ft-Gallatin Valley-
Madison River Valley-Missouri Headwaters.

&&

$$

http://www.weather.gov/greatfalls