Damaging Wind and High Wind in Montana, August 17, 2021

Area Forecast Discussion
National Weather Service Great Falls MT
1138 AM MDT Tue Aug 17 2021

...AVIATION SECTION UPDATED...

.UPDATE...
10:25AM Update: Updated to include Red Flag Warning for eastern
Beaverhead National Forest.

8:40AM update: Main change this quick update was to put some slight
chance/isolated POPs along the western part of the CWA from I-90
northward, to account for activity that has popped up over western
Montana and is pushing into our forecast area. Otherwise, the
forecast appears to be mostly on track, and T/Td/RH were tweaked for
current conditions and trends. Will need to watch for central and
northeastern parts of the CWA not getting as warm as advertised,
owing to winds shifting behind the front and encroaching cloud cover.

&&

.SYNOPSIS...
A strong cold front will drop south across the region through the
day today, which will help to usher in the cooler temperatures
and widespread precipitation for the Northern Rockies. Expect
periods of rain and some high mountain snow through Wednesday.
Slightly warmer air moves back into the region towards the end of
the week, as the precipitation becomes more scattered.

&&

.DISCUSSION...
Today through Wednesday...Overall the current forecast is on track.
A strong cold front continues to move southward through the region.
Temperatures in the Cut Bank area today will likely not rise much,
while it will still be a very warm day over parts of Southwest MT. A
few morning sprinkles will transition to scattered thunderstorms
this afternoon over Central/Southwest MT. Some storms could produce
some strong wind gusts, mostly over Southwest MT. Rain develops
along the front range of the Rockies by late afternoon, and
gradually moves eastwards towards Central MT this evening.
Precipitation amounts still look on track from previous forecasts,
with general 0.50 to 1.50 inch rainfall falling west of a line from
Helena to Havre. East of this line, rainfall amounts will be lower.
Snow will generally accumulate above 8000 feet tonight over the
Rocky Mountain front, with any snow accumulation generally less than
an inch. Expect well below normal temperatures on Wednesday across
the entire region.

Thursday through Tuesday...Overall some warming of the temperatures
is expected, but still most areas will have below normal
temperatures through next Tuesday. Rainfall chances still look a bit
uncertain this weekend, but the GFS is looking rather wet once again
for much of the western half of the region from Friday night into
Saturday. Scattered rain showers are possible into the early
portions of next week across. Brusda

&&

.AVIATION...
1116 AM MDT Tue Aug 17 2021 (17/18Z TAF period)

Variety of flight rules xpctd thru the 18z TAF period with worst
restrictions expected tonight into Wed.

Sct non-impactful -SHRA may occur across N Cntrl MT early this aftn
with impactful convection possibly dvlpng by late aftn vcnty
KBZN/KEKS. This expected late day activity should spread NE across
KGTF and surrounding aerodromes early this evening. Overnight, a
large area of RA should affect all but KLWT/KHVR with vsbys and
CIGs lowering once steadier rain becomes established. Brief
periods of +RA are probable. Precip intensity and coverage should
begin to wane Wed mrng, but areas of -RADZ will likely persist
nearly areawide ...along with MVFR to perhaps IFR CIGs and VSBYs.
Renewed moderate SHRA may occur vcnty KBZN on Wed aftn.

Sfc front will continue to push southward across MT this afternoon
with gusty NNWrly sfc winds in its wake. SSWrly sfc winds to the
south of the front and Erly sfc winds to the east of the front.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  71  46  55  43 /  60 100  90  20
CTB  57  44  54  40 /  80 100  70  10
HLN  79  48  58  48 /  70 100  90  40
BZN  88  48  61  45 /  40  90  90  60
WYS  80  49  62  40 /  20  80  90  60
DLN  86  45  58  41 /  40 100  90  50
HVR  82  48  58  46 /  40  90  70  20
LWT  85  47  55  46 /  50  80  90  50

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until midnight MDT tonight Gallatin National
Forest.

Red Flag Warning until 9 PM MDT this evening Eastern Beaverhead
National Forest.

&&

http://www.weather.gov/greatfalls