Wildfire and High Wind in Montana, March 28 to 29, 2021

Area Forecast Discussion
National Weather Service Great Falls MT
1155 PM MDT Sat Mar 27 2021

Aviation Section Updated

.UPDATE...

No significant adjustments to current overnight/Sunday morning
forecast.

The main overall change was to increase cloudiness to reflect the
increasing high then mid level cloudiness over north central and
central Montana. Winds are also remaining quite gusty up toward
Cut Bank this evening, so have increased them a bit for the
remainder of the evening to reflect this, but there is a good
chance that they will decouple for a few hours late this evening
before increasing again after midnight as winds aloft strengthen
with the strengthening surface pressure gradient.
Coulston

&&

.SYNOPSIS...
Mild and dry but increasingly windy conditions are expected through
Sunday. A strong cold front will move through the region Sunday
night, bringing the strongest winds along with rain and snow
showers. Intense snow and strong winds could affect some areas as
the front moves through Sunday night with much colder temperatures
and additional snow showers possible on Monday. A return to dry and
milder conditions is expected to follow for the rest of next week.

&&

.AVIATION...
1155 PM MDT Sat Mar 27 2021 (28/00Z TAF period)

Main concern will be the strong winds developing Sunday
morning/afternoon over much of North Central/Southwest MT...followed
by a strong cold front passage early Monday morning with snow.
Surface winds could gust over 40 knots at many terminals on Sunday.
Blowing dust could impact some airports over North Central MT, and a
visibility restriction might be needed on later TAF's. Then a very
strong cold front moves through the region on Monday morning between
06z and 12z. Expect a wind shift to the west/northwest, with snow
accompanying the front. Visibility could be less than 1 mile for a
short time. Mountains passes will start to become obscured on Sunday
evening. Brusda

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

&&

.FIRE WEATHER...
Strong winds, low humidity and unseasonably warm temperatures will
lead to critical fire weather conditions across most lower
elevation/grassland areas on Sunday. The most critical conditions
look to be across areas from northern Lewis and Clark and Teton
counties east across Cascade and Choteau counties where afternoon
humidity will likely fall below 20% and recent precipitation has
been minimal. Hoenisch

&&

.PREV DISCUSSION...
/ISSUED 618 PM MDT Sat Mar 27 2021/

Multiple weather hazards are on track to impact the region Sunday
and Monday as a fairly potent shortwave disturbance emerging in
the Gulf of AK today dives southeast downstream of an amplifying
ridge in the the eastern Pacific, crossing the northern Rockies
and MT Sunday night.

Weak ridging in place ahead of this feature will bring dry and
increasingly mild conditions through Sunday with afternoon
temperatures reaching the mid to upper 60s on Sunday for most
areas under the increasing southwest flow aloft. Strong winds will
develop tonight along the Rocky Mtn front and adjacent areas and
spread across much of north-central and central MT by mid-day
Sunday in response to the strengthening surface pressure gradient
across the Rockies and increasing winds aloft. By Sunday afternoon
and evening, deeper mixing from daytime heating will likely
result in fairly widespread strong and gusty winds across the
entire area, including most of SW MT. Strongest winds aloft move
across the region Sunday evening just ahead of the mid-level
shortwave and surface cold front approaching from the NW with the
wind speed maximum aloft shifting south through Central and SW MT
Sunday night. Peak wind gusts in excess of 70 mph are likely for
areas along and adjacent to the Rocky Mtn Front including areas as
far east as Cut Bank. Peak gusts of 60-70 mph are likely for the
rest of north-central and SW MT Sunday afternoon and evening. In
addition to the difficult travel for some motorists in strong
crosswinds and fire weather hazards (discussed below), areas of
blowing dust are a possibility as well, especially near any
recently cultivated fields or areas with loose soil. With
increasing confidence in the widespread coverage of strong winds,
have upgraded the remaining high wind watches to warnings.

The frontal passage Sunday night will bring a quick change to
winter weather hazards for some areas in addition to the
continued very windy conditions. The front looks to reach areas
along the continental divide Sunday evening with precipitation
initially limited to areas near the divide, expanding east as the
front progresses south and eastward across central and SW MT
Sunday night. Instability along the front and strong forcing with
the associated shortwave brings the potential for convective
precipitation with the frontal passage, which could result in some
brief but intense periods of snow, especially over the mountain
passes near the divide. In addition, convective elements along the
front may bring down strong winds aloft with strong pressure
rises behind the front also contributing to the widespread very
windy conditions into Monday morning.

Cold, moist and unstable northwest flow aloft follows the frontal
passage across the region on Monday as the upper level trough
traverses the State. Daytime temperatures on Monday will be
around 30 degrees colder than Sunday and in the 30s to around 40
for most areas. Snow showers will be most persistent over the
mountains Monday with mainly scattered snow showers elsewhere. A
secondary push of colder air south into north-central MT Monday
morning could bring a period of more widespread light snow to
portions of N-central MT, with northerly upslope flow potentially
bringing an inch or two of snow accumulation to areas from Great
Falls to Lewistown. Upper level troughing lingers over the region
into Tuesday with temperatures recovering some but remaining below
seasonal averages. Upper level ridging looks to rebuild for the
remainder of next week for a return to dry and milder conditions
beginning Wednesday. Hoenisch

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  39  67  25  36 /  10   0  50  60
CTB  34  57  20  32 /  10  10  70  60
HLN  37  68  31  38 /  10   0  70  40
BZN  30  66  29  38 /  10   0  70  40
WYS  17  51  16  33 /   0   0  60  70
DLN  29  62  24  35 /   0   0  60  20
HVR  35  66  23  35 /   0   0  30  40
LWT  32  63  24  32 /   0   0  60  50

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from noon Sunday to noon MDT Monday Blaine...
Cascade...Central and Southern Lewis and Clark...Chouteau...
Eastern Teton...Fergus...Hill...Judith Basin...Liberty...Meagher.

Red Flag Warning from 9 AM to 8 PM MDT Sunday Eastern
Glacier/Toole/Central/Eastern Pondera/Liberty...Lewis and Clark
National Forest Rocky Mountain District-Rocky Mountain Front.

High Wind Warning from 3 PM Sunday to noon MDT Monday
Beaverhead...Broadwater...Gallatin...Jefferson...Madison.

Red Flag Warning from 1 PM to 7 PM MDT Sunday Eastern Beaverhead
National Forest.

Red Flag Warning from 9 AM to 8 PM MDT Sunday Central and
Eastern Lewis and Clark National Forest Areas...Chouteau and
Fergus Counties...Hill and Blaine Counties.

High Wind Warning from 6 AM Sunday to 6 AM MDT Monday Eastern
Glacier...Eastern Pondera...Toole.

High Wind Warning from midnight tonight to 6 AM MDT Monday
Northern Rocky Mountain Front...Southern Rocky Mountain Front.

&&

http://www.weather.gov/greatfalls