Severe Thunderstorm Warning 63, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
340 PM MDT Tue Aug 29 2023

.SYNOPSIS...

Dry, breezy, and very warm conditons are expected through late this
afternoon and evening when a Pacific cold front brings a period of
gusty showers and thunderstorms that will persist into the overnight
hours. Much cooler, showery, and windy conditions are then expected
Wednesday into Thursday. Temperatures warm back above average for
the first half of the weekend as widely scattered showers and storms
increase in a southwest to northeast fashion through Sunday.

&&

.UPDATE...

A Severe Thunderstorm Watch has been issued and is in effect until
900 PM MDT this evening for Beaverhead and Madison Counties.

The primary threats include scattered damaging wind gusts to 70
mph possible, and isolated large hail to 1 inch in diameter
possible.
- Fogleman

&&

.AVIATION...
520 AM MDT Tue Aug 29 2023 (29/12Z TAF Period)

VFR conditions prevail through this afternoon beneath an increasing
southerly flow aloft with just some scattered mid level clouds.
Higher concentrations of wildfire smoke across NE MT may briefly
affect KHVR this morning with MVFR visibility. Southerly surface
winds increase at all terminals this afternoon through this evening
ahead of a Pacific cold front expected to cross the region this
evening and overnight. Strong wind gusts are possible with showers
and thunderstorms associated with the frontal passage along with a
period of lower ceilings and mountain obscurations. West winds
develop overnight behind the front and increase through the day on
Wednesday. Hoenisch

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

&&

.PREV DISCUSSION...
/ISSUED 225 PM MDT Tue Aug 29 2023/

After a slow start eroding morning inversions, temperatures are
starting to rise toward forecast highs and winds and humidity are
now yielding marginally critical fire weather conditions over the
northeastern portions of the CWA. The very warm and dry conditions
will persist through this evening when the well advertised
Pacific front, currently approaching Western Montana, will
traverse the forecast area from west to east between 5 pm and
midnight tonight. Locations west of I15 are still expected to see
the strongest gusts from the cold front and associated showers and
thunderstorms and gusts up to 70 mph can't be ruled out with the
stronger cells. SPC has maintained a 'slight risk' (15% chance
within 25 miles of a given point) for wind gusts over 58 mph for
much of Beaverhead County. Atmospheric instability will fall off
as the front moves eastward later this evening, but there will
still be sufficient cold air advection and overall frontal
momentum to transfer at least isolated instances of severe wind
gusts over the plains and the eastern portions of Southwest
Montana. Tracking this evening's severe weather will be on the
tricky side as there may not be a lot of lightning or heavy rain
with today's showers/storms and wind gusts may outrun the cells
themselves by quite a distance.

The front should clear the CWA by Wednesday morning with cooler
but windy conditions across the area Wednesday through Thursday as
the upper low center lifts out through NW MT into southern AB.
30-45 mph wind gusts are expected across much of Central and
Southwest Montana Wednesday through early Thursday. The strongest
winds are still expected along the immediate east slopes of the
Rocky Mtn Front and the downslope areas over and near the central
ranges where there is a greater than 50% probability of gusts
exceeding 55 mph. Strongest winds in these areas will likely occur
tonight during a period of more favorable conditions for
downslope wind enhancement. A High Wind Warning was issued for the
Rocky Mtn Front, the northern high plains, and Cascade/Judith
Basin County lower elevation zones for Wednesday through noon
Thursday. There will be periods of strong wind potential separated
by lulls within this timeframe.
- RCG/Hoenisch

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  57  71  52  77 /  60  30  30   0
CTB  56  64  52  73 /  90  40  40  10
HLN  57  74  53  80 /  80  20  20   0
BZN  52  76  45  78 /  70  10  10   0
WYS  42  66  32  69 /  50  10   0   0
DLN  47  70  40  75 /  80   0   0   0
HVR  60  76  53  81 /  70  40  40  20
LWT  55  75  50  77 /  80  20  10   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from 6 AM Wednesday to noon MDT Thursday for
Eastern Glacier, Western Toole, and Central Pondera-Northern
High Plains-Southern High Plains.

Red Flag Warning until 1 AM MDT Wednesday for Hill and Blaine
Counties.

High Wind Warning from 10 AM Wednesday to noon MDT Thursday for
Cascade County below 5000ft-Judith Basin County and Judith Gap.

&&

http://www.weather.gov/greatfalls