588
FXUS65 KTFX 240002
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
600 PM MDT Thu May 23 2024

UPDATED AVIATION SECTION

.SYNOPSIS...

Unsettled conditions will continue through the end of the work
week and weekend, with temperatures running below normal and
chances for showers, thunderstorms, and at times mountain snow.

&&

.DISCUSSION...

600 pm update... The Flood Watch for the Little Belt and Highwood
Mountains was cancelled earlier, as rainfall was not quite as heavy
as originally expected, much of the precipitation fell as snow in
the mountains, and there has been very little movement in river and
creek levels so far. Snow has also mostly ended or decreased to non-
impactful levels in the mountains of Central and Southwest Montana,
so the remaining Winter Storm Warnings for those areas were
cancelled after 430 pm. -Coulston

Rest of today through tonight...upper level disturbance over North
Central Wyoming and its associated surface low over Western South
Dakota will continue to slide east and away from the Northern
Rockies through the evening hours tonight. This will lead to
decreasing precipitation across Southwest Montana through the
remainder of the afternoon hours, with additional snow accumulations
of 1-2" and isolated amounts approaching 4" across the remaining
Winter Storm Warnings for the Bridger, Gallatin, and Madison Ranges.
Clear skies during the early morning hours over the plains of
Southern Alberta, North Central Montana, and northern portions of
Central Montana allowed temperatures to warm into the 50s, which
combined with unstable northwesterly flow aloft and an embedded
wave tracking southeast through the flow has allowed scattered
showers and isolated thunderstorms to develop. These showers and
storms will track slowly east through the overnight hours tonight,
bringing brief periods of heavy rain and the potential for small
hail. A brief cold air funnel can not also be ruled out given H500
temperatures approaching -25C and the presence of existing vorticity
associated with the longwave trough and secondary closed (H500) over
Alberta and Saskatchewan. Should any cold air funnel form they would
be brief and pose no danger to the public or infrastructure.
-Moldan

Tomorrow through Memorial Day is favored by ensemble model guidance
to continue to see unsettled weather conditions through the Memorial
Day weekend in terms of scattered rain showers and thunderstorms.
Tomorrow is favored along the Hi-Line down to Great Falls and
Lewistown for scattered thunderstorms as an upper level shortwave
is forecasted to move across North Central Montana tomorrow
afternoon and quickly depart our area (Fergus and Blaine
Counties) by Saturday night. Then, models are favoring another
upper level trough to move in for Saturday and Sunday across
Southwest and North Central Montana with more coverage of rain
shower and thunderstorm activity. Sunday afternoon and early
evening can be periodically breezy with wind gusts as high as 40
mph across the Hi-Plains region as our upper level trough begins
to depart to our east. Primary concerns for thunderstorm
development this weekend is going to be lightning, heavy
downpours, small hail size, and gusty erratic winds. Temperatures
this weekend are also going to remain unseasonably cool with highs
in the 50s and 60s and lows in the 30s (20s in mountainous
terrain).

Monday into Tuesday morning, upper level ridging is favored by
latest ensemble model guidance to build back into the region and
bring dry conditions with warm afternoon temperatures. Latest
National Blend of Models 4.2 Probabilistic data suggests high
temperatures reaching over 80 degrees for Tuesday is high (>75
percent) for locations from Great Falls to Havre down to Helena.
Wednesday afternoon and evening into the end of next week, ensemble
model guidance is still uncertain on the exact path of upper level
troughing across our region. Upper level troughing could come down
from Canada and bring more unsettled weather conditions to our
region or it could remain to our north. What is currently favored is
a cold front from the Pacific Northwest to move across our region
Wednesday and Thursday bringing temperatures back to near normal
(60s and low 70s) for the end of May. Webb

&&

.AVIATION...
24/00Z TAF Period

VFR conditions are mostly expected across North Central (KCTB,
KHVR), Central (KLWT, KGTF, KHLN), and Southwest (KBZN, KEKS, KWYS)
Montana through at least 25/00Z, unless otherwise mentioned.

The storm system that brought widespread precipitation to the area
has mostly exited to the east, leaving scattered to broken clouds
and decreasing winds in its wake. However, a disturbance in the
resulting northwest flow aloft will bring scattered showers and a
few thunderstorms to much of North Central Montana overnight, mainly
north of a KGTF-KLWT line, where brief periods of MVFR conditions
are possible with the showers. Otherwise, skies will partially clear
over Central and Southwest Montana, mainly after midnight, allowing
patchy fog to form in the areas where winds will become light,
mainly in the southwest valleys, where periods of IFR conditions are
possible. Weak instability will redevelop over the plains again in
the northwest flow aloft after 16Z, bringing gusty northwest surface
winds and another chance for showers and thunderstorms. -Coulston

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  39  63  40  65 /  30  30  10  60
CTB  39  60  37  62 /  70  50  10  40
HLN  37  65  42  64 /  10  20  10  70
BZN  26  62  36  62 /  10  20  10  70
WYS  23  54  30  52 /  10  10  10  80
DLN  27  61  36  58 /  10  10  20  70
HVR  42  63  39  69 /  60  60  10  50
LWT  33  60  37  62 /  10  40  10  80

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

http://www.weather.gov/greatfalls