High Wind in Montana, December 8, 2021

Area Forecast Discussion
National Weather Service Great Falls MT
1102 PM MST Tue Dec 7 2021

Updated Aviation Discussion

.SYNOPSIS...

The colder airmass that has been across the region will retreat
today with most areas warming to near or slightly above seasonal
averages by this afternoon, except for areas along and north of the
Milk River, where colder air will linger into this evening. Strong
southwest winds develop along the east slopes of the Rockies this
evening with very windy and also mild conditions spreading across
the area on Wednesday before a cold front bring cooler conditions
again Wednesday night through the rest of the week.

&&

.UPDATE...

Pressure falls in Alberta will continue overnight as an upper
level system approaches from the west-northwest. This is causing a
tightening surface pressure gradient along the east slopes of
the Rocky Mountains to accelerate surface winds through gaps in
the terrain, mountain passes, and canyons. Additionally, mountain
top level winds have strengthened significantly over the last 6
hours. These forces will work together to create another period of
strong and gusty winds along the Rocky Mountain Front and over
the adjacent plains. At this time, it appears that the existing
High Wind Warning has a good handle on the situation. However,
mountain top level winds appear to be trending a bit faster and
moving in a bit sooner than anticipated. As such, I have updated
the forecast to increase winds over the mountains of the
Continental Divide for the remainder of tonight through early
Wednesday evening. Lower elevation winds over the plains were
increased slightly but omega values suggest that there will
probably not be enough downward motion to bring the stronger
mountain top level winds to the plains. I have also increased
overnight PoPs/QPF/Weather along the Continental Divide as radar
imagery suggests that orographic lift will continue to squeeze
precipitation out of the abundant Pacific moisture caught up in
the flow aloft. mpj

&&

.AVIATION...
1102 PM MST Tue Dec 7 2021 (08/00Z TAF period)

Main impact to aviation over the next 24 hours will be winds as
strong westerly flow aloft moves across the region along with
several emebedded disturbances. Surface winds remain southwesterly
through Wednesday morning before turning more westerly by mid-day as
the first disturbance moves across the area. Strongest winds will be
confined to ridgetops and areas along the east slopes of the Rockies
through most of tonight before expanding east across adjacent
portions of north-central MT Wednesday morning. Most areas will see
gusty westerly winds by Wednesday afternoon with winds turning a bit
more from the northwest Wednesday evening as a second disturbance
moves through the area. VFR conditions prevail at most terminals
with precipitation and mountain obscuration primarily along the
Continental Divide before some showers move east with the
disturbance Wednesday evening. Moderate to severe mountain wave
turbulence is possible through the period with areas of low level
wind shear also possible through Wednesday morning. Hoenisch

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

&&

.PREV DISCUSSION...
/ISSUED 440 PM MST Tue Dec 7 2021/

After a brief cooldown, above normal temperatures have returned to
most of the area today (with the exception of areas along the Hi-
Line) as upper level ridging builds in. Aside from the warmth,
today will be generally quiet across the area, with just some of
the usual breezes across the North-Central Plains.

This upper level ridge will begin to break down tomorrow,
resulting in gusty winds across the plains though the strongest
winds will be focused along the Rocky Mountain Front as usual.
High Wind Warnings remain out for the Rocky Mountain Front,
including all of Glacier County, for the high winds. Outside of
the Warned area, expect wind gusts up to 50 mph, though a
localized 60 mph wind gust or two can't be entirely ruled out.
Otherwise, Wednesday should be a fairly dry day save for a few
isolated snow showers, mainly over the Southwestern Mountains.

Upper level troughing will set up across the area for Thursday and
Friday, but this will only be a brief cooldown with little in the
way of precipitation. Temperatures across the area will be in the
low 30s both days, which is near to slightly below average for
this time of year.

As we head into the weekend, an upper level trough will dig just
offshore of the Pacific Northwest Coast, and its associated jet
streak (with 500 mb winds near 100 kts) will move overhead. With
this jet streak overhead, another widespread wind event looks
probable, which will likely require High Wind Watches to be
hoisted in future updates, as there is the potential for
widespread wind gusts to 60 mph at the surface. Winds should
weaken at some point on Sunday as the system works further south,
with the southwesterly flow aloft bringing yet another round of
unseasonable warmth to the area with most of the area seeing highs
in the 40s Saturday through at least Monday. Ludwig

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  32  46  20  34 /   0   0  10   0
CTB  26  41  16  28 /  10  10  30   0
HLN  30  48  22  34 /   0  20  10   0
BZN  26  46  17  32 /   0  30  30   0
WYS  24  33  12  24 /  30  60  80  20
DLN  27  45  15  29 /   0  40  10   0
HVR  11  43  16  31 /  10   0  50   0
LWT  25  44  17  31 /   0  10  10   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from 2 AM to 8 PM MST Wednesday Eastern
Glacier.

High Wind Warning until 8 PM MST Wednesday Northern Rocky
Mountain Front...Southern Rocky Mountain Front.

&&

http://www.weather.gov/greatfalls

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
824 PM MST TUE DEC 7 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0600 PM     NON-TSTM WND GST 14 W BYNUM              47.98N 112.61W
12/07/2021  M58 MPH          TETON              MT   MESONET

            MESONET STATION DELMT DELLWO (MCSCN).

1121 AM     NON-TSTM WND GST 8 SE EAST GLACIER PARK  48.36N 113.11W
12/07/2021  M74 MPH          GLACIER            MT   MESONET

            MESONET STATION DCRM8 DEEP CREEK RAWS.

0708 PM     NON-TSTM WND GST 1 ENE EAST GLACIER PARK 48.45N 113.20W
12/07/2021  M63 MPH          GLACIER            MT   MESONET

            MESONET STATION MTBRN TWO MEDICINE BRIDGE
            (MT DOT).

&&