Special Weather Statement, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
304 PM MDT Tue Aug 25 2020

.SYNOPSIS...

Smokey haze persists across the area today as smoke continues to
flow in from from the SW. Showers and thunderstorms will move
through the area this afternoon and evening. Looking into
tomorrow, another round of showers and thunderstorms will be
possible over Southwest Montana, but will mostly remain over the
mountains.

&&

.DISCUSSION...

Showers and thunderstorms are beginning to develop over Western
Montana this afternoon as daytime heating continues to destabilize
the atmosphere. These showers and thunderstorms should begin to
push into the area over the next few hours, and with additional
development expected over the mountains in the southern half of
our CWA, we should have a decent sized area of thunderstorms move
through the southeastern 2/3 to 3/4 of the CWA. SPC continues to
maintain a marginal risk for severe weather over the southern
portion of our CWA, which makes sense given the very dry boundary
layer and DCAPE values between 800-1000 J/kg in that area.

Tomorrow will feature another round of showers and thunderstorms
over the SW mountains as another jet streak passes through.
However, because this jet streak will be quite a bit weaker than
the jet streak currently moving overhead, showers and
thunderstorms should be a bit more limited. That said, the
boundary layer will remain quite dry, so a few strong outflow wind
gusts will remain possible.

As upper level ridging begins to build in for the weekend, quieter
weather should take hold for Thursday and Friday, though Thursday
could feature a few gusty winds as the upper level ridge begins to
push in. Eyes at this point will be on what happens as this ridge
breaks down over the weekend, as there remains the potential for
a rather significant trough to take its place on Sunday. With that
being said, there remains a huge degree of uncertainty with how
exactly this system will play out. Both the GFS and the ECMWF
models have had huge swings on how they handle this system, with
some runs showing a widespread rain (and even some mountain snow),
while the following runs show next to nothing in terms of
precipitation. The two things that seems fairly certain is that
there is the potential for some gusty winds and that temperatures
will be much cooler in the wake of this system, with some lower
elevation locations likely struggling to get into the 60s on
Monday.

Ludwig

&&

.AVIATION...
1200 PM MDT Tue Aug 25 2020 (25/18Z TAF Period)

VFR/MVFR conditions overspread Central MT this afternoon as smoke
continues to flow into the area. This will continue through the day
today, with visibilities generally remaining over 5SM at all
terminals, though a few brief periods of lower visibilities are
possible. In addition to the smoke, TSRA are expected to develop
during the afternoon today, moving eastward into the evening. TSRA
today could bring strong downdrafts and outflows, especially south
of KHLN. TSRA should clear the area after midnight for most of the
area, though a few may linger south of KHLN. -Ludwig

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

NOTE: Amendments not scheduled for Ennis (KEKS) do to ongoing
runway closure.

&&

.FIRE WEATHER...
Showers and thunderstorms are expected this afternoon and evening.
While these showers and thunderstorms may produce locally heavy
rain, fire starts will be possible, especially if lightning
strikes occur away from the parent thunderstorms. In addition,
gusty outflow winds will be possible with any thunderstorm due to
a very dry boundary layer, which could cause any new lightning
starts to be fanned and ongoing fires to behave erratically. This
situation will play out again on Wednesday as more showers and
thunderstorms develop over the mountains.

Thursday and Friday will be quieter days, with seasonably warm
temperatures. However, northern regions may see some gusty winds
on Thursday, accompanied with low RH values. This will create
heightened fire danger, but winds should remain below Red Flag
Warning criteria.

More critical fire weather is possible this weekend as the current
upper level ridge begins to break down as an upper level trough
moves in from Canada. As this occurs, gusty winds are possible,
and will need to be monitored for fire weather products later this
week.

Ludwig

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  55  85  53  83 /  50   0  20  10
CTB  50  82  48  80 /  10   0   0   0
HLN  52  84  52  85 /  50  30  40  20
BZN  51  85  50  84 /  60  20  50  40
WYS  39  80  41  77 /  50  10  70  60
DLN  49  80  48  79 /  60  20  40  40
HVR  56  88  53  86 /  40   0  10   0
LWT  54  82  54  82 /  70  10  50  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
&&

http://www.weather.gov/greatfalls

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