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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS65 KTFX 250931
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
331 AM MDT Thu Apr 25 2024

.SYNOPSIS...

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Today there will be rain in Southwestern Montana before
the next system moves into the area tomorrow. That system will bring
heavy snow to the mountains of Southwestern Montana on Friday and
Saturday and lower-elevation rain to the area. A series of upper-
level disturbances will impact the area on Sunday and Monday. By
the middle of next week it will warm up slightly.
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&&

.DISCUSSION...

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Today through Saturday... Today there is southwest flow
aloft with an embedded shortwave. This shortwave will bring
rain/snow to Southwestern Montana which could come via an isolated
thunderstorm. Today along and south of the Montana Highway 200
Corridor and west of US Highway 287 south of Three Forks there is a
10 - 20% chance for a tenth of an inch of rain or greater. For the
lower-elevations from Three Forks to the Bozeman area south to the
Idaho Border there is a 20 - 50% chance of a quarter inch of rain or
greater on Thursday. For the Gallatin and Madison ranges there is a
20 - 40% chance for a tenth of an inch of snow or greater on
Thursday.

On Friday an upper-level trough will begin to move over
North-central, Central, and Southwestern Montana. This will bring
cooler temperatures and precipitation to the area. Isolated
thunderstorms will be possible in Southwestern Montana on Friday.
The lower-elevations of Southwestern Montana have a 15 - 35% chance
of receiving a half inch of rain or greater. The lower-elevations of
Central Montana have a 15 - 40% chance for a quarter inch of rain or
greater. This upper-level trough will remain in place over North-
central, Central, and Southwestern Montana on Saturday. This storm
will bring heavy snow to the mountains of Southwestern Montana.
The higher elevations of the mountains have a 80% chance for
receiving 8 inches or more snow from Friday to Saturday. The
mountain peaks have a 70% chance for receiving a 12 inches or more
snow from Friday to Saturday. As a result, a Winter Storm Warning
is in effect for the Gallatin and Madison ranges and Northwest
Beaverhead County from 6 AM Friday until 6 PM Saturday. A Winter
Weather Advisory is in effect for the Ruby Mountains and Southern
Beaverhead Mountains from 6 AM Friday until 6 PM Saturday. On
Saturday the lower-elevations of Central and Southwestern Montana
have a 30 - 50% chance for receiving a quarter inch of rain or
greater. Some of the lower-elevations of Southwestern Montana
could see a few flakes of snow mix in with the rain. On Saturday
North-central Montana has a 10 - 30% chance for receiving a
quarter inch of rain or greater. The mountains of North-central
and Central Montana will see a rain/snow mix on Friday and all
snow for the most part on Saturday. On Saturday the mountains of
North-central and Central Montana have a 35 - 50% chance for
receiving an inch or more snow.

Sunday through Monday...On Sunday above North-central, Central, and
Southwestern Montana there will be zonal flow with a shortwave
trough embedded in it. This will allow temperatures to warm back up
to slightly above seasonal averages. The shortwave trough will
cause isolated light rain to occur across North-central, Central,
and Southwestern Montana. There is a 10 - 20% chance for a tenth
of an inch of rain or greater across the lower-elevations of
Central and Southwestern Montana along and south of the Montana
Highway 200 Corridor. On Sunday there will be a strong surface
pressure gradient and so there will be gusty winds along the Rocky
Mountain Front. There is 50 - 70% chance for wind gusts exceeding
55 mph on Sunday along the Northern Rocky Mountain Front. On
Monday there is an upper-level trough and associated weak cold
front that moves through the area. This will slightly cool off
temperatures and bring rain and snow to Southwestern Montana. Due
to the cold front there is a 70 - 90% chance for wind gusts
exceeding 55 mph along the Rocky Mountain Front on Monday. On
Monday across the lower-elevations of Southwestern Montana there
is a 10 - 35% chance for a tenth of an inch of rain or more. On
Monday across the Mountains of Southwestern Montana there is a 75%
chance for a tenth of an inch of snow or greater.

Tuesday through next Thursday... On Tuesday clusters indicate that
an upper-level ridge begins to move over North-central, Central, and
Southwestern Montana. This will warm up temperatures slightly with
dry conditions across the area. On Wednesday three clusters (87% of
ensemble members) indicate that there will be an upper-level ridge
in place over North-central, Central, and Southwestern Montana. The
other cluster (13% of ensemble members) has zonal flow over the
area. On Thursday clusters indicate that there will be an upper-
level ridge in place over North-central, Central, and Southwestern
Montana. This indicates that most likely temperatures will warm back
up across the area for Wednesday and Thursday. -IG
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&&

.AVIATION...
1145 PM MDT Wed Apr 24 2024 (25/06Z TAF Period)

A few light showers will move through the CWA overnight, but impacts
will be minor. On Thursday, there is a small potential for
thunderstorms, mostly south of a line from Ennis to Big Sky. Thus I
kept TS out of the terminals for now. Showers will become a bit more
widespread by Thursday evening south of I-90 as well. Generally
just passing clouds expected over North Central MT Thursday
afternoon. Mountains/passes could become obscured by Thursday
evening over Southwest MT.

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

&&

.PRELIMINARY POINT TEMPS/POPS...
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GTF  66  41  57  41 /  10  10  50  60
CTB  63  36  51  36 /   0   0  30  30
HLN  67  42  56  40 /  10  20  70  70
BZN  66  39  52  36 /  50  70  90  80
WYS  54  33  48  31 /  80  80  90  70
DLN  62  40  53  36 /  30  50  80  80
HVR  70  40  64  39 /   0   0  10  20
LWT  64  40  54  37 /  20  30  50  50
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&&

.TFX WATCHES/WARNINGS/ADVISORIES...
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Winter Storm Warning from 6 AM Friday to 6 PM MDT Saturday for
Gallatin and Madison County Mountains and Centennial Mountains-
Northwest Beaverhead County.

Winter Weather Advisory from 6 AM Friday to 6 PM MDT Saturday
for Ruby Mountains and Southern Beaverhead Mountains.
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&&

$$

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