Special Weather Statement, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
307 PM MDT Sat Aug 14 2021

.SYNOPSIS...

It will remain hot and very dry through Monday, and winds will
increase for Sunday and Monday, as well. A major change in the
weather pattern is then expected to arrive by Tuesday, with
a widespread soaking rain and shift to much cooler than normal
weather for mid-week. Rain chances will diminish and temperatures
will moderate some late in the week, but it is still forecast to
remain a bit cooler than normal.

&&

.DISCUSSION...

This evening through Monday night...
The axis of an upper level ridge continued to work its way
towards Central Montana. Even though smoke has suppressed temps a
bit, this ridging still allowed for another rather warm day
today. As of 3pm, temps were already into the 90s as of 3pm for
most of the Plains and some central valleys, and valleys of
Southwestern Montana were expected to get into at least the upper
80s, if not low 90s. Despite smoke likely suppressing highs by a
few degrees, relative humidity has dropped to critical levels
below 15% across most of the area, but generally light winds
should keep critical fire weather danger at bay. Unfortunately,
and as expected, the smoke has returned east of the Divide with a
vengeance, with Helena, Great Falls, and Cut Bank all reporting
visibility under 6 miles as of 3pm.

This upper level ridge will begin to break down on Sunday, and
while temperatures will still remain quite warm, winds will begin
to increase as the ridge flattens. Expect another day with highs
in the 90s, and with RH values expected to once again dip into
the lower teens, widespread critical fire weather conditions are
anticipated. Thus, in collaboration with GGW and BYZ, the Fire
Weather Watch was upgraded to a Red Flag Warning. The warning is
valid for all Fire Weather Zones for Sunday, though Zone 116
(Lincoln Ranger District) was excluded for Monday, owing to higher
expected relative humidity. Critical fire weather conditions are
expected across most of the area again Monday - temperatures may
be a few degrees cooler owing to the deteriorating ridge, and RH
may be a touch higher. However, winds are forecast to be a bit
stronger, balancing out the slightly better RH and maintaining
widespread critical fire weather conditions. -Kredensor

Tuesday through next Saturday...
A strong cold front will push through the area on Tuesday as an
upper level trough digs into the Pacific Northwest. This front
will cause temperatures to crash, with daytime highs likely only
reaching the mid 60s for most of the plains. Southwest Montana may
get into the 80s again on Tuesday, as the mountains will hold up
the front and it may not reach there until late Tuesday evening,
or even overnight. Rain showers will also accompany the colder
air, and snow levels may fall low enough to allow for some early
season snow across some of the higher terrain. While there is
still a bit of uncertainty with rainfall totals, there will be a
good chance of picking up over 0.5 inches of liquid across the
plains, though valleys in Southwest Montana appear to be more in
the 0.1-0.25 inch range as of this time. Regardless, it will be a
welcome, widespread and wetting rain that should help
significantly curtail current fire activity (and new fire starts
for a while) and help things green up a bit. As we head into the
latter part of the week, expect the cooler air to stick around for
a few days, with another potential shot of rain coming for the
end of the week. Ludwig/Kredensor

&&

.AVIATION...
1100 AM MDT Sat Aug 14 2021 (14/18Z TAF period)

Main impact to terminal operations throughout the next 24 hours
will be VIS reductions in areas of smoke/haze. While VFR conditions
are primarily expected throughout the 1418/1518 TAF period, areas
of dense smoke could reduce VIS down to MVFR for brief periods of
time. Given low confidence and generally low predictability in smoke
forecasting, I have elected to maintain VFR prevailing groups for
now with this TAF issuance. Mountains will be obscured at times. -
Moldan

&&

.FIRE WEATHER...

Critical fire weather conditions are expected across most of the
fire weather forecast area both Sunday and Monday. Even with smoke
cover likely suppressing temperatures a bit today, humidity is
critical at under 15% for much of the area. However, winds have
not been too strong today, so all critical thresholds are not
being met, though certainly fire weather conditions are elevated,
and fires are likely seeing some increased activity.

For Sunday, it will be another very warm day, with widespread
highs in the 90s. Humidity will be under 15% for most locations in
the afternoon and early evening hours, and winds will also pick
up. Expect widespread sustained winds tomorrow of 15 to 20 mph,
with areas of 25 mph or more. Gusts of 25 to 30 mph will be common
on Sunday, with even stronger gusts up towards Glacier County and
Fire Weather Zone 112. For Monday, RH may not be quite as low, but
winds are expected to be a bit stronger, thus balancing out and
keeping conditions critical and worthy of an RFW. -Kredensor

&&

.CLIMATE...
With a high in the 90s again today, Helena will tie its all-time
record for number of 90-degree days - 47 days - which was set in
2001. With an anticipated high in the 90s on Sunday and Monday,
they should break the record.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  61  97  64  94 /   0   0   0  10
CTB  59  92  62  85 /   0   0   0   0
HLN  63  97  64  95 /   0   0   0  10
BZN  54  94  56  93 /   0   0   0  20
WYS  45  84  43  82 /  10   0   0  30
DLN  52  89  54  89 /   0   0   0  30
HVR  64  98  67  94 /   0   0   0   0
LWT  60  94  62  92 /   0   0   0  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon to 9 PM MDT Sunday Lincoln Ranger
District of the Helena National Forest.

Red Flag Warning from noon Sunday to midnight MDT Monday night
Central and Eastern Lewis and Clark National Forest Areas...
Chouteau and Fergus Counties...Eastern
Glacier/Toole/Central/Eastern Pondera/Liberty...Helena and
Townsend Ranger Districts of the Helena National Forest...Hill
and Blaine Counties...Lewis and Clark National Forest Rocky
Mountain District-Rocky Mountain Front.

Red Flag Warning from noon Sunday to midnight MDT Monday night
Gallatin National Forest.

&&

http://www.weather.gov/greatfalls

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