Damaging Winds and High Wind in Montana, August 4, 2022

Area Forecast Discussion
National Weather Service Great Falls MT
1120 AM MDT Thu Aug 4 2022

...Aviation Section Updated...

.SYNOPSIS...

Hot, dry, and windy conditions will continue across the Northern
Rockies through today. Winds will be especially strong along the
Rocky Mountain Front and east to the Interstate 15 corridor in
North Central Montana. Scattered to numerous showers and
thunderstorms are expected this afternoon and evening, mainly
along and southeast of a Lincoln, to Great Falls, to Havre line.

&&

.UPDATE...
Observed minimum temperatures this morning for areas east of the
Rocky Mountain Front were 5 to 10 degrees F warmer than
forecasted and current satellite imagery shows developing cumulus
along the ID/MT border. No changes to the temperature and wind
forecast were made this morning with high wind gusts still
expected for today. Minor adjustments were made to PoPs for this
afternoon for North Central MT as confidence increases for
scattered showers and thunderstorm development this afternoon and
evening. Increased PoPs in Blaine and Fergus counties as
confidence grows for showers and thunderstorms this evening to
develop and move northeastward into those areas. Webb

&&

.AVIATION...
1120 AM MDT Wed Aug 3 2022 (04/18Z TAF period)

VFR conditions continue to prevail under high-level clouds through
the morning. Thereafter, scattered to numerous showers and
thunderstorms are expected to develop across Southwest Montana
between 18-22z extending northeastward to portions of central
Montana, which may lead to brief periods of MVFR conditions. Primary
impacts to terminals will be gusty, erratic winds. At approximately
the same time, winds will be increasingly stronger at all terminals,
but especially across the plains. Expect mountain wave turbulence
along the Rocky Mountain Front through this evening. A weak cold
front will cause winds to become northerly from north to south
across the area beginning around 11z/Fri at KCTB to around 16z/Fri
at KLWT.

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

&&

.FIRE WEATHER...

A Red Flag Warning remains in effect until 9 PM Thursday across
all TFX fire weather zones. Windy, dry, and warm conditions are
expected each afternoon through Thursday evening, which in
combination with receptive fuels, would make any fire starts
difficult to put out. Cooler temperatures and lighter winds are
expected Friday and Saturday.

Upper ridging builds back over the area this weekend into Monday,
but models appear in good agreement with a ridge breakdown
sometime around the middle of next week as an upper trough moves
into the Pacific Northwest, with timing ranging from as early as
Tuesday to as late as Thursday of next week. This is a known fire
weather watchout for winds and thunderstorm activity in the
Northern Rockies region. Stay tuned.

&&

.PREV DISCUSSION...
/ISSUED 510 AM MDT Thu Aug 4 2022/

Today through tonight...primary forecast concerns are High Winds,
Fire Weather, and isolated severe thunderstorms.

Anomalously strong mid-level flow associated with a H500 longwave
trough, which is currently moving over the Pacific Northwest and
British Columbia coasts this morning, will overspread the Northern
Rockies from this morning and through the evening hours tonight.
NAEFS analysis indicates that H700 wind speeds will be 3 to 4
standard deviations above normal northwest of a Lincoln, to Great
Falls, to Havre line through this evening, with the remainder of
Southwest through North Central Montana being 1 to 2 standard
deviations above normal. Expectation is that winds will begin to
increase rapidly between 15-18z across the CWA with increasing solar
insolation and resulting mixing, with strong and gusty winds then
persisting across the region through 00-03z tonight. A High Wind
Warning remains in effect for the Rocky Mountain Front, Eastern
Glacier, Toole, Liberty, and Eastern Pondera from 12/18z today
through 03z tonight, with Hill County also being added to the
warning this morning as confidence in winds reaching warning levels
has increased here (especially for western portions of the county
[i.e. Inverness area]). This High Wind event more closely resembles
one that would be seen during the late fall and/or winter, and could
be especially impactful given the presence of foliage, which could
lead to tree damage given the increased surface areas of the trees.

The strong southwest to west winds combined with hot temperatures
(80s to near 100 degrees) and dry conditions (relative humidity
values as low as 7-12%) will also lead to critical fire weather
conditions across the entire CWA through this evening, with the
potential for new or existing fires to spread very rapidly. This
will be especially true over the plains where grasses are cured
and a wind driven fire run could be difficult to contain.

Finally, monsoonal moisture rotating around the H500 high over the
Great Basin/Desert Southwest will bring scattered to numerous
showers/thunderstorms over Southwest and eastern portions of Central
and North Central Montana (mainly along and southeast of a Lincoln,
to Great Falls, to Havre line) through this evening. A Marginal Risk
for severe thunderstorms exists over eastern portions of Southwest,
Central, and North Central Montana today, with the primary concern
being the potential for damaging wind gusts given inverted-v
profiles and the presence of strong mid-level flow. - Moldan

Friday through Saturday...cooler air, with high temperatures near to
below normal, will overspread the Northern Rockies through the first
half of the upcoming weekend. Precipitation chances will also be
possible both day across most of the CWA, especially south of the
Interstate 90 corridor in Southwest Montana. Some thunderstorms on
Friday could produce locally heavy rainfall, and for this reason WPC
has portions of Southwest Montana under a Marginal Risk for
Excessive Rainfall. - Moldan

Sunday through next Thursday...upper level ridging will begin to
build back into the Northern Rockies, which lead to high
temperatures rising back into the 90s to near 100 degrees. Monsoonal
moisture pivoting northeast and over southern portions of the
Northern Rockies will also provide for isolated to scattered showers
and thunderstorms, especially from Tuesday through Thursday. -
Moldan

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  95  55  82  52 /  10  10  10  20
CTB  84  49  73  46 /   0   0  10  10
HLN  96  56  86  52 /  30  20  20  30
BZN  95  54  86  53 /  40  40  50  50
WYS  84  48  76  47 /  40  50  70  60
DLN  89  53  84  51 /  40  20  40  40
HVR  97  55  79  51 /  10  10  10  20
LWT  94  56  80  51 /  40  40  30  40

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 9 PM MDT this evening Central and Eastern
Lewis and Clark National Forest Areas...Chouteau and Fergus
Counties...Gallatin National Forest...Helena and Townsend Ranger
Districts of the Helena National Forest...Lincoln Ranger
District of the Helena National Forest.

High Wind Warning until 9 PM MDT this evening Eastern Glacier...
Eastern Pondera...Hill...Liberty...Toole.

Red Flag Warning until 9 PM MDT this evening Eastern
Glacier/Toole/Central/Eastern Pondera/Liberty...Hill and Blaine
Counties...Lewis and Clark National Forest Rocky Mountain
District-Rocky Mountain Front.

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

High Wind Warning until 9 PM MDT this evening Northern Rocky
Mountain Front...Southern Rocky Mountain Front.

&&

http://www.weather.gov/greatfalls