801
FXUS65 KTFX 171605
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1005 AM MDT Wed Jul 17 2024

.SYNOPSIS...
The warm and generally dry conditions will persist for the time
being across Southwest, Central, and North Central Montana, along
with a chance of showers and thunderstorms each day, mainly over
the mountains of Southwest and Central Montana. Most of these
storms will produce very little rainfall. However, a disturbance
will bring a chance of showers and thunderstorms to most of the
area on Thursday, with a slightly better chance of measurable
rainfall remaining over the plains.

&&

.UPDATE...
No update planned for this morning, current forecast is on track.
Isolated thunderstorms still possible this afternoon, mostly over
the mountains. Otherwise, expect another very warm day over the
CWA. Brusda

&&

.AVIATION...
17/12Z TAF Period

VFR conditions are generally expected to continue through at
least 18/12Z across Southwest (KWYS, KEKS, KBZN), Central (KHLN,
KGTF, KLWT), and North Central (KHVR, KCTB) Montana. However,
smoke from area wildfires will continue to cause periods of
reduced slantwise visibility, mainly from KHLN south through
Southwest Montana. Daytime heating will also cause density
altitude issues across the entire area, mainly between 18Z and
03Z.

The overall weather pattern will be dominated by a high pressure
ridge centered over the Northern Rockies, allowing a few
thunderstorms with little if any rainfall to develop over the
mountains of Southwest and Central Montana and the Rocky Mountain
Front between 20Z and 02Z. However, winds aloft will be fairly
light, so they may only move slightly off the mountains. These
storms will be very hit-or-miss, and the likelihood that they
will directly impact most terminals is low; therefore, have only
mentioned PROB30s at KEKS, KWYS, and KLWT. One concern is possible
indirect impacts from gusty outflow winds of up to 30 kt, mainly
along a KHLN to KLWT line and south through Southwest Montana.
Storms should generally dissipate after 02Z.
-Coulston

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

&&

.PREV DISCUSSION...
/ISSUED 300 AM MDT Wed Jul 17 2024/

Today through Friday... The strong high pressure ridge will
remain in place over North Central, Central, and Southwest
Montana today, allowing temperatures to warm up to 10 degrees
above normal. This heating should help develop isolated
thunderstorms with erratic wind gusts and little precipitation
over the mountain areas this afternoon into early this evening,
but light winds aloft will likely keep them from moving out onto
the plains. The axis of the surface thermal trough will remain
over the Northern Rockies, which will keep breezy easterly winds
over much of North Central and Central Montana, where occasional
gusts to 35 mph are possible.

A disturbance will then move from the Pacific Northwest today,
over the ridge tonight, and across the region on Thursday. The
associated increased lift, dynamics, and instability associated
with it will bring a chance of thunderstorms to most of the area.
Despite widespread afternoon humidity values falling into the 15
to 25 percent range, forecast precipitable water values of around
1 inch over the plains are 1 to 2 standard deviations above
normal, making a mix of wet and dry thunderstorms more likely.
However, in the mountain valleys, humidities will fall more so
into the teens and precipitable water values will be less (0.50 to
0.75 inches), making thunderstorms with dry lightning more likely
there, prompting the Storm Prediction Center to include that area
in a risk for isolated dry thunderstorms. Regardless, erratic
wind gusts up to 35 mph will be possible with any storms once
again. The exiting disturbance will take most of the thunderstorms
with it Thursday night. The ridge is then forecast to rebuild
into the area on Friday, bringing a situation similar to today,
where any isolated thunderstorms that do develop will mostly
remain over the mountains due to lighter winds aloft. The passage
of the disturbance will also cool temperatures a few degrees over
those expected today, but it will not be a significant cooldown.

Saturday through next Wednesday... Ensemble clusters indicate
that the high pressure center of the ridge is forecast to
retrograde west from the Four Corners into the Southwestern United
States. However, they also forecast that a shortwave trough will
gradually approach the Pacific Northwest coast during this same
timeframe, which will keep the ridge axis over the Northern
Rockies. As a result, the National Blend of Models is forecasting
a gradual warmup of temperatures back to around 10 degrees above
normal by Tuesday and Wednesday with daily chance of showers and
thunderstorms mainly over the mountains of Southwest and Central
Montana. However, these forecast temperatures continue to mostly
remain below record levels and below Heat Advisory criteria.
-Coulston

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  95  63  93  60 /  10  10  20  10
CTB  93  60  90  56 /  10  20  20  10
HLN  98  63  98  63 /  10  10  10   0
BZN  95  57  95  57 /  10  20  10  10
WYS  86  45  85  45 /  30  10  20  10
DLN  91  54  92  54 /  10  10  10   0
HVR  95  63  94  60 /  10  10  30  30
LWT  90  59  90  56 /  20  40  30  30

&&

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

&&

$$

http://www.weather.gov/greatfalls