483
FXUS65 KTFX 130620
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1220 AM MDT Tue Aug 13 2024

Aviation Section Updated

.SYNOPSIS...
Showers and thunderstorms will occur through at least Friday across
at least some portion of North-central, Central, and Southwestern
Montana. The showers and thunderstorms will be the most widespread
on Tuesday. Isolated thunderstorms Tuesday afternoon and evening
could produce severe wind gusts, large hail, and heavy rainfall. A
cold front moves through on Tuesday which cools down temperatures on
Wednesday.

&&

.UPDATE...
Main update to the overnight forecast period was to keep mention of
scattered showers and weak thunderstorms through around midnight
across much of North Central and Southwest Montana to better reflect
current activity. SPC analysis still shows moderate instability over
the area. However, the threat for additional strong to severe
thunderstorms with strong wind gusts and large hail has decreased
significantly. Another adjustment was to increase mention of fog in
areas that received significant precipitation with this afternoon`s
thunderstorms, which mainly includes areas of North Central Montana
along and just south of US Highway 2. -Coulston

&&

.AVIATION...
13/06Z TAF Period

Isolated thunderstorms will affect North Central MT early this
morning. Widespread showers/thunderstorms will affect the entire CWA
on Tuesday afternoon. Thus tempo groups already introduced. Brief
heavy rainfall/gusty winds/lightning will be the main impact. The
storms exit the CWA late Tuesday evening. Mountains/passes will be
obscured by either smoke or clouds through the period. Brusda

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

&&

.PREV DISCUSSION...
/ISSUED 613PM MDT Mon Aug 12 2024/

This afternoon through Tuesday... This afternoon an upper-level
ridge remains over North-central, Central, and Southwestern
Montana. This afternoon through this evening an upper-level level
shortwave moves through the upper-level flow. This will cause
there to be showers and thunderstorms in the Golden Triangle
region (the region from Cut Bank to Havre to Great Falls) and
Southwestern Montana through this evening. This afternoon the
Storm Prediction Center (SPC) has issued a Marginal Risk for
severe weather (5% chance for severe wind gusts within 25 miles
of point) for the Golden Triangle region, Madison and Gallatin
Counties, and eastern Beaverhead County. Isolated thunderstorms
will produce severe wind gusts (wind gusts greater than 58 mph).
The upper-level ridge remains over North-central, Central, and
Southwestern Montana through Tuesday morning before an upper-level
trough begins moving over the area Tuesday afternoon. A cold
front associated with the upper-level trough will move through
North-central, Central, and Southwestern Montana Tuesday afternoon
through early evening. On Tuesday the SPC has issued a Marginal
Risk for severe weather (5% chance for severe wind gusts and a 5%
chance for golf ball-sized hail withing 25 miles of point) for
eastern Beaverhead, southeastern Madison, and Gallatin Counties
and Eastern Fergus and Blaine Counties. Isolated thunderstorms
will produce severe wind gusts (wind gusts greater than 58 mph)
and hail the size of golf balls (primarily in eastern Beaverhead,
southeastern Madison, and Gallatin Counties). Some thunderstorms
will produce heavy rainfall. On Tuesday locations across
Southwestern Montana have a 20 - 50% chance for receiving a
quarter inch of rain or greater. On Tuesday locations in Central
Montana have a 30 - 60% chance for receiving a tenth of an inch
of rain or greater.

Wednesday through Friday... On Wednesday the upper-level trough
remains over North-central, Central, and Southwestern Montana.
This will allow for showers and thunderstorms in the afternoon
and evening across the area. Due to the cold front that moves
through on Tuesday temperatures will be 5 to 10 degrees below
seasonal averages across the lower-elevation`s of North-central,
Central, and Southwestern Montana on Wednesday. On Wednesday
locations across Southwestern Montana have a 40 - 60% chance for
receiving a tenth of an inch of rain or greater. On Thursday an
upper-level ridge moves back over North-central, Central, and
Southwestern Montana. However, an upper-level shortwave moves
through the upper-level flow and will bring showers and
thunderstorms to the area. On Thursday all lower-elevations of
North-central, Central, and Southwestern Montana have a 20 - 40%
chance for a tenth of an inch of rain or greater. On Friday the
upper-level ridge remains over North- central, Central, and
Southwestern Montana. However, an upper- level shortwave moves
through the upper-level flow and will bring showers and
thunderstorms to the area.

Saturday through next Monday... On Saturday clusters show an
upper- level ridge over North-central and Central Montana with an
upper- level trough beginning to move over the area. This will
keep similar weather on Saturday to Friday. On Sunday and Monday
deterministic models and clusters begin to diverge. This will
continue to be monitored for details. -IG

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  55  83  56  79 /  10  40  50  20
CTB  52  82  54  79 /  30  20  20  20
HLN  56  83  55  79 /  20  60  50  40
BZN  50  80  49  78 /  30  60  60  50
WYS  42  70  39  69 /  10  80  60  80
DLN  49  76  46  73 /  10  70  50  50
HVR  56  89  59  85 /  30  20  40  20
LWT  52  83  52  76 /  20  30  60  40

&&

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

&&

$$

http://www.weather.gov/greatfalls