496
FXUS65 KTFX 211844
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1244 PM MDT Fri Jun 21 2024

.SYNOPSIS...
Thunderstorms develop and move through the area, today. Some
thunderstorms are forecast to become severe, producing gusty and
erratic strong winds, large hail, frequent lightning and periods of
heavy rain. A warming trend is forecast for the next few days. By
Sunday, low elevation highs range in the 90s.

&&

.DISCUSSION...

Key Points:

-Strong to severe thunderstorms are expected this afternoon and
 evening across North Central Montana, bringing the potential for
 destructive hail, strong winds, and even a low chance of a
 tornado

-Upper level ridging builds in next week, bringing warm and dry
 conditions to the Treasure State

Through Sunday Big concern in the short term continues to be the
potential for strong to severe thunderstorms, especially across
the North Central Plains south of US-2. Satellite imagery late
this morning was showing an early start to the convection along
the US-2 corridor and over the Little Belt Mountains, with dew
points across the plains creeping up into the mid 50s, indicating
that sufficient low level moisture is in place across the plains
to support these storms as they begin to grow through the
afternoon and evening hours. Given current forecast atmospheric
profiles (aka soundings), the atmosphere seems to be primed for
the development of a few scattered supercell thunderstorms, thanks
to modest but present directional shear and ample instability
(with CAPE/instability values nearing/exceeding 1500-2000 J/kg,
which is a bit higher than values we usually see in this area),
with wind speed with height (hodographs) indicating that the winds
in the atmosphere will be supportive of rotating
updrafts/supercells. While supercells are capable of producing any
type of severe weather, including strong winds, destructive hail,
and tornadoes, the atmosphere appears most primed for destructive
hail and potentially wind, depending on if the supercell winds
are actually able to reach the ground. While a tornado or two
cannot be ruled out, this threat should be held back by cloud
bases generally above 3000 feet above the ground. However, cloud
bases will be a little lower in the Judith Gap/Lewistown/Grass
Range area, which may make the atmosphere a bit more favorable to
the development of a tornado, if a supercell is able to make full
use of the atmospheric dynamics, especially with the presence of
an existing boundary from yesterdays storms that moved through
the area. Storms will remain possible through the afternoon and
evening hours before weakening and/or moving eastward by midnight
or so.

Across the southwest today, expect a few showers and
thunderstorms, especially across the higher terrain, though upper
level flow will be less conducive to the longer lived type of
storms that will be found across the plains.

Beyond today, upper level ridging will begin to build in across
the Intermountain West, which will allow temperatures to be on the
increase through the weekend. Expect most areas to reach the 80s
on Saturday with all but the Plains adjacent to the Rocky Mountain
Front reaching the low to mid 90s on Sunday with relative
humidity values dipping into the low 20s and teens. Ludwig

Monday through Wednesday...In response to the building upper level
closed area of higher heights over Arizona/New Mexico, an upper
level ridge dominates The Treasure State. Low elevation high
temperatures continue in the 80s and 90s, through mid-week, while
conditions remain dry for our region.

Thursday and Friday...As the end of the week approaches, the next
upper level trof enters the region, temperatures cool a bit, and
widespread rainfall is forecast.
- Fogleman

&&

.AVIATION...
21/18Z TAF Period

Main concern this afternoon/evening will be the potential for severe
storms over North Central MT. The main threat from any severe storm
will be large hail/strong winds. There is also small probability of
an isolated tornado in the Havre/Lewistown areas. Storms are
developing currently at 18z, with the storms to become most
widespread/active around 00z Sat. Overall, most storms will diminish
between 03z and 06z Sat. There is a small potential for fog on
Saturday in morning in any areas that have heavy rain on Friday
evening. For now, kept fog out of the TAF, as the probability is too
low at this time. Mountains/passes over Central MT could be obscured
for a few hours by passing storms through 06z. Brusda

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  49  82  55  92 /  30   0   0   0
CTB  44  80  50  85 /  30   0   0   0
HLN  53  87  57  96 /  10   0   0  10
BZN  49  85  53  95 /  10   0   0  10
WYS  40  78  44  84 /  10   0   0  10
DLN  47  85  51  91 /   0   0   0   0
HVR  49  82  55  94 /  60  10   0  10
LWT  48  77  54  90 /  50  10   0  20

&&

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

$$

http://www.weather.gov/greatfalls