324
FXUS65 KTFX 221120
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
520 AM MDT Sat Jun 22 2024

UPDATED AVIATION SECTION

.SYNOPSIS...

A high pressure ridge building into Southwest, Central, and North
Central Montana will keep the area mostly dry through the weekend,
as temperatures warm to between 10 and 20 degrees above normal by
Sunday with gusty southwest winds. However, a few showers and
thunderstorms are possible each afternoon over and near the
mountains of Central and North Central Montana. A disturbance
will then flatten the ridge for Monday into Tuesday, shifting the
chance for a few thunderstorms to the mountains of Southwest
Montana, and cooling temperatures 5 to 10 degrees.

&&

.DISCUSSION...

Today through Sunday... The remainder of the weekend will be much
more quiet than Friday weatherwise. Clearing skies this morning
An upper level ridge of high pressure will build north through
Southwest, Central, and North Central Montana today into Sunday,
which will keep much of the area dry, and allow temperatures to
warm to between 10 and 20 degrees above normal by Sunday. A weak
disturbance on the leading edge of the ridge may bring a few
showers and weak thunderstorms to the eastern portion of the
forecast area (mainly east of a Havre to Lewistown line). As the
ridge axis starts moving east across the area on Sunday ahead of
an approaching low pressure trough, the more southwesterly flow
aloft will bring another chance for showers and thunderstorms to
that same area. A surface frontal boundary will also shift east
into Central Montana, which may provide enough of a focusing
mechanism to cause a few strong thunderstorms with erratic wind
gusts and hail. Therefore, the Storm Prediction Center (SPC) has
put that area under a Marginal risk for severe thunderstorms on
Sunday.

Another concern on Sunday will be the combination of heat, low
relative humidity, and increasing southwest winds at lower
elevations. Temperatures there will mostly warm into the 90s,
increasing the heat risk somewhat. However, low afternoon
relative humidity, along with the fact that record highs will be
approached but likely not broken, will limit the risk for
hazardous heat. Afternoon humidity values in the 15 to 25 percent
range along the east slopes of the Rockies and south into the
valleys of Southwest Montana will combine with increasing
southwest winds (greater than 60 percent probability of at least
25 mph sustained winds) to increase fire weather concerns,
especially for those who may have recreational fires or
agricultural burns. However, recent systems that have moved
through the area have produced significant precipitation, which
has slowed the drying of available fuels, limiting fire danger
somewhat. Regardless, caution should be used on Sunday with any
burning.

Monday through Wednesday... The upper level ridge will maintain
most of its strength as the shortwave trough moves east through
the area on Monday. This should help weaken the trough and put
the area under more of a westerly flow aloft. A weak cold front
will also move through the area on Monday, which should help cool
temperatures about 5 to 10 degrees over those on Sunday, and help
shift the breezy winds more westerly. Afternoon humidity will be
similarly low to that from Sunday, but the probability for
similarly strong winds will be lower. This shortwave passage will
also shift the potential for a few showers and weak thunderstorms
south into the mountains of Southwest Montana. After the
shortwave exits the area to the east, the high pressure ridge
will gradually build back into the region Tuesday into Wednesday.
This should keep conditions dry with less wind, as lower
elevation temperatures warm back into the lower 80s to lower 90s.

Thursday through next Saturday... Ensemble model clusters for
their 00Z run on June 22nd are in fairly good agreement with
their solution for Thursday and Friday. They show a moderately
strong low pressure trough moving across the Pacific Northwest on
Thursday into the Northern Rockies and Northern High Plains on
Friday. This results in the National Blend of Models (NBM)
forecasting near to slightly below normal temperatures to end the
week with a persistent chance of showers and thunderstorms.
However, the relative weakness of the trough likely indicates that
significant cooling and precipitation is unlikely at this time,
but the situation will need to be monitored.
-Coulston

&&

.AVIATION...
22/12Z TAF Period

VFR conditions will continue through at least 23/12Z across North
Central (KCTB, KLWT), Central (KLWT, KGTF, KHLN), and Southwest
(KBZN, KEKS, KWYS) Montana, unless otherwise mentioned.

High pressure aloft building in over the area will keep skies mostly
clear with only some passing mid- and high-level cloudiness. Patchy
fog that has developed in areas of light wind will dissipate after
15Z, but the likelihood that MVFR or IFR conditions will directly
impact any terminal is low. Surface winds will mostly remain light,
but southwest to west wind gusts up to 25 kt are possible at the
KEKS and KWYS terminals between 18Z and 24Z. Increasing
southwesterly winds aloft will also cause some mountain wave
turbulence after 00Z. -Coulston

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  81  55  93  54 /   0   0   0   0
CTB  80  50  85  48 /  10   0   0   0
HLN  87  58  96  58 /   0   0  10  10
BZN  85  53  94  54 /  10   0  10  10
WYS  78  44  84  47 /   0   0   0   0
DLN  85  51  91  53 /   0   0   0   0
HVR  82  56  93  55 /   0   0  10  10
LWT  77  54  91  53 /  10  10  20  20

&&

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

$$

http://www.weather.gov/greatfalls