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566
FXUS65 KTFX 211000
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
400 AM MDT Fri Jun 21 2024

.SYNOPSIS...

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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.
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&&

.DISCUSSION...

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Note: The forecast area for the National Weather Service Great
Falls Weather Forecast Office includes north central, central and
southwest Montana.

Today...A low amplitude upper level trof enters our region, today.
An unstable atmosphere with deep layer 35KT to 40KT wind shear
favorable for the development of severe thunderstorms is
forecast. There is high confidence that some of these
thunderstorms will become severe, producing gusty and erratic high
winds, large hail, frequent lightning and periods of heavy rain.
Although it looks like these storms will move through the area at
a decent pace, some localized flash flooding is possible.

Saturday through Sunday...A weak upper level ridge builds into the
area, favoring warming and drying. By Sunday, low elevation high
temperatures push into the 90s, with minimum Relative Humidity
values falling into the teens. Sunday, the next upper level trof
approaches from the west; however, a building bubble of high
pressure over Arizona/New Mexico, adds mass to the trof, allowing
most of it`s energy to be directed northward into Canada. A few
thunderstorms and rain showers develop on Sunday.

Monday through Wednesday...In response to the building upper level closed
area of higher heights over Arizona/New Mexico, an upper level
trof 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
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&&

.AVIATION...
21/06Z TAF Period

VFR conditions are mostly expected through at least 22/06Z across
North Central (KCTB, KHVR), Central (KLWT, KGTF, KHLN), and
Southwest (KBZN, KEKS, KWYS) Montana, unless otherwise mentioned.

A weakly unstable southwesterly flow aloft will mainly move mid- and
high-level cloudiness over the area through at least 15Z; a few
light showers or weak thunderstorms are also possible, but
confidence that any will directly impact terminals is low, so have
not mentioned them in the TAFs. However, the airmass will become
increasingly moist and unstable after 15Z as a shortwave low
pressure trough approaches from the west. This will bring at least
scattered showers and thunderstorms to the area along and east of a
line from the Continental Divide southeast through the KHLN and KBZN
terminal areas. Some storms may become strong to possibly severe at
times over the plains between 18Z and 02Z, mainly east of a KCTB to
KGTF line, where heavy rain and lower ceilings could cause periods
of MVFR conditions. These stronger storms could also bring hail and
strong erratic wind gusts. Showers and storms will start to decrease
from the west after 00Z as the shortwave moves through the area,
which will also bring some mountain wave turbulence as the westerly
flow aloft increases. -Coulston

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

&&

.PRELIMINARY POINT TEMPS/POPS...
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GTF  76  50  82  55 /  60  20   0   0
CTB  72  44  81  51 /  70  30   0   0
HLN  83  53  88  58 /  30  10   0   0
BZN  81  48  85  52 /  20  10   0   0
WYS  76  41  79  45 /  10  10   0   0
DLN  80  47  85  51 /   0   0   0   0
HVR  76  49  82  56 /  60  60  10   0
LWT  72  47  77  54 /  70  50  10   0
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&&

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

$$

http://www.weather.gov/greatfalls