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483
FXUS65 KTFX 240933
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
333 AM MDT Mon Jun 24 2024

.SYNOPSIS...

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A westerly flow aloft will generally keep North Central, Central,
and Southwest Montana dry and slightly warmer than normal today
with gusty southwesterly winds. A high pressure ridge building
back into the area is forecast to decrease winds Tuesday into
Wednesday, as temperatures get quite warm again Wednesday.
However, a low pressure trough will bring cooler and more
unsettled weather starting Wednesday night and continuing into
Friday.
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&&

.DISCUSSION...

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Today through Tuesday... A moderate westerly flow aloft in the
wake of a Pacific cold front will keep most of North Central,
Central, and Southwest Montana dry today. However, weak
instability over a portion of Southwest Montana this afternoon
may combine with some weak embedded energy to develop a weak
thunderstorm or two over the mountains of Madison and Gallatin
Counties that should move east into South Central Montana. The
westerly winds aloft may also partially translate down to the
surface along the Rocky Mountain Front, over Hill and Blaine
Counties, and as more southerly winds through some valleys of
Southwest Montana. However, the more aggressive short term
ensemble guidance only gives a 60+ percent probability of 40+ mph
gusts there, so High Wind criteria (58+ mph gusts) should not be
exceeded. A high pressure ridge is then forecast to build into
the area on Tuesday, which should help decrease winds aloft and
at the surface.

Temperatures will mostly be 5 to 10 degrees cooler than those on
Sunday, but that still makes them 5 to 10 degrees above seasonal
averages. Low afternoon humidity will also cause fire weather
concerns, especially today with the breezy winds, but analysis
shows that fuel moistures are still in the moderate range.

Also of minor concern is that we have received reports that the
Gallatin River near the town of Logan is running somewhat high,
but it is not threatening any land around there as of yet.

Wednesday through Friday... A low pressure trough is forecast to
move into the Pacific Northwest on Wednesday, which should help
amplify the high pressure ridge over Montana and cause
temperatures to warm up similar to those we had on Sunday.
However, two sources of increasing moisture will increase coverage
of a Moderate Heat Risk. Mid-level moisture in a southwesterly
flow aloft ahead of the trough will likely combine with moisture
in a southeasterly low-level flow ahead of a Pacific cold front
to keep humidity from falling quite as low as that on Sunday. As
of now, though, the coverage of Moderate Heat Risk is still not
enough for a Heat Advisory yet. With this increased moisture and
instability, the timing of the cold frontal passage Wednesday
night into Thursday will be crucial as to whether or not there
will be strong to severe thunderstorms. If it occurs overnight,
there will be less of a chance of it, but the chance increases if
it occurs during the daytime heating on Thursday. Regardless,
ensemble guidance indicates that precipitable water values are
forecast to be between 1 and 2 standard deviations above normal,
so heavy downpours seem likely from storms that do develop.

As the low pressure trough moves into the area Thursday into
Friday, temperatures are forecast to fall to near seasonal
averages on Thursday, than to around 10 degrees below normal on
Friday. The chance for showers is also forecast to shift more so
out onto the plains on Friday with an overall decrease in
thunderstorms, as cooler temperatures will decrease the amount of
instability available.

Saturday through next Monday... Ensemble cluster analysis
indicates that a slightly more progressive weather pattern will
develop with less amplified features. This results in a weak high
pressure ridge keeping Saturday and Saturday night dry as
temperatures warm back to just above normal by Sunday. However, a
shortwave trough is forecast to follow close behind the ridge
Sunday afternoon into Monday, bringing slightly cooler than normal
temperatures and another round of at least scattered showers and
thunderstorms. -Coulston
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&&

.AVIATION...
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24/06Z TAF Period

Note: The NWS Great Falls Weather Forecast Office manages the
following TAFs: KCTB, KHVR, KGTF, KLWT, KHLN, KBZN, KEKS and
KWYS.

VFR conditions continue at all airfields. Periods of gusty
southwesterly to northwesterly winds are forecast, with the
strongest winds forecast to occur across The Northern Rocky
Mountain Front where winds gust to as high as 50KT, during the
early part of this TAF period. Mountain wave is forecast. This
afternoon widespread winds to 30KT/35KT are forecast across the
region. Although confidence in thunderstorm activity overhead our
airfields is too low to include the mention of thunderstorm in
our TAFs, it should be noted that there is a 10% or greater
chance that a few thunderstorms develop, this afternoon/evening,
across portions southwest and central Montana, most notably:
Madison, Gallatin, Meagher, Judith Basin and Fergus Counties.
With today`s low elevation highs in the upper 80s, density
altitude impacts are forecast for a line from KHLN to KBZN and
south.
- Fogleman

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

.PRELIMINARY POINT TEMPS/POPS...
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GTF  82  48  80  51 /   0   0   0   0
CTB  76  45  77  48 /   0   0   0   0
HLN  88  54  88  57 /   0   0   0   0
BZN  88  49  87  54 /   0   0   0   0
WYS  81  43  81  48 /  10   0   0  10
DLN  85  48  87  53 /   0   0   0   0
HVR  82  49  80  51 /   0   0   0   0
LWT  79  48  77  50 /   0   0   0   0
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&&

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

$$

http://www.weather.gov/greatfalls