High Wind in Montana, September 24, 2020

Area Forecast Discussion
National Weather Service Great Falls MT
1135 AM MDT Thu Sep 24 2020

...Aviation Section Update...

.SYNOPSIS...

Smoke aloft will move over the area this morning, but the passage
of a cold front will move the smoke out of the area and bring
strong westerly winds with mountain precipitation. A westerly flow
aloft will continue breezy, but not strong, westerly winds through
the weekend with mainly mountain showers. High pressure will then
likely warm temperatures above normal with dry conditions for
early next week.

&&

.Morning Update...

Update has been published, with only minor changes made to the
on-going forecast. High winds and fire weather concerns will
continue to be the primary concern throughout the day today,
especially across North Central, Central, and portions of
Southwest Montana. Winds so far this morning have gusted between
60 and 70 mph along the Rocky Mountain Front and out as far as the
I-15 corridor in Toole county, with these winds expected to
transition further east throughout the remainder of the morning
and into the afternoon hours as the upper level trough and
Pacific cold front slide across the region. Moisture recovery
during the overnight hours last night was very poor to poor in the
downslope areas of the North Central and Central Montana, with
continued low relative humidity values expected over the plains
ahead of and even behind the passage of the Pacific front.
Finally, upslope precipitation has filled in nicely along the
Continental Divide this morning, with this precipitation expected
to remain fixed to the terrain throughout most of the day. -
Moldan

&&

.AVIATION...
1135 AM MDT Thu Sep 24 2020 (24/18Z TAF Period)

Expect VFR conditions throughout this TAF periods at all airfields
with the exception of KEKS and KWYS where conditions are forecast to
fall into the MVFR range due to smoke. Reduced visibility in smoke
is forecast to resolve after 25/06Z. Expect intermittent light rain
showers at KHVR through 24/20Z. Periods of obscuration are forecast
in mountian showers, in association with a frontal passage. Expect
strong gusty winds, today. Low level winds shear is included in the
KCTB TAF. Expect all associated turbulence.

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

NOTE: Amendments not scheduled for Ennis (KEKS) due to ongoing
runway closure.

&&

.FIRE WEATHER...

The Red Flag Warning for the TFX fire weather area (excluding
FWZ116) will now start at 9 am MDT, but it will still run until 9
pm MDT this evening. The reasoning for this was due to the fact
that humidity recovery over the plains has been fairly poor (35 to
45 percent western plains, but 50 to 65 percent eastern plains)
and the humidity should fall into the 20 to 30 percent range over
the dry grasslands as the strong westerly winds spread east
across the area this morning into early this afternoon. Cooler air
will also move in behind the front, but the strong winds will
mitigate any gradual increase in humidity to likely maintain
critical fire weather conditions. Humidity should recover more
significantly this evening as winds remain breezy but decrease
somewhat. Coulston

&&

.PREV DISCUSSION...
/ISSUED 545 AM MDT Thu Sep 24 2020/

Today through tonight...
Overall, the windy forecast remains on track. Southwest winds
aloft will continue to increase ahead of a low pressure trough
approaching the region from the Pacific coast. A cold front ahead
of this system will also move through the area this morning into
early this afternoon, but the tail-end of it will linger over
Southwest Montana into early this evening. The main impact from
this frontal passage will be the translating of the strong
southwest, then west, winds down to the surface, especially over
the plains of North Central Montana. Mid level winds are not
forecast to be quite as strong as previously expected compared to
previous model runs, but widespread 45 to 55 mph winds should
yield similar wind gusts with the frontal passage, and gusts of 60
mph at times are quite possible. The chance of these stronger wind
gusts is high enough that expanding the High Wind Warning over all
of the plains seemed reasonable. Have decided to start this at 9
am MDT this morning to better match the eastward progression of
the front. Winds downsloping off the Rocky Mountain Front will
enhance wind gusts mostly to 65 mph over the adjacent plains, but
more favored areas close to the Front itself could see gusts up
to 80 mph, so no change to High Wind Warning timing there (still
beginning at 6 am MDT). The broadening low pressure trough will
continue as a moderate westerly flow aloft overnight, so although
the strong winds will decrease, they will remain breezy.
Precipitation with the frontal passage will be persistent through
tonight over the Continental Divide, but the downsloping winds
will keep much of the area dry, except for a few light showers
reaching the southwest valley floors with the frontal passage.

Friday through Sunday...
Weak upper level ridging will decrease lingering mountain showers
into Friday morning, but a shortwave trough will move across the
area Friday afternoon through Saturday. This should bring a good
chance of mainly mountain showers once again, as westerly
downslope winds remain quite breezy and should limit showers over
the plains.

Monday through next Thursday...
A high pressure ridge off the California and Oregon coasts should
then move east onshore and strengthen over the Pacific coast
states into the Great Basin and Intermountain West through this
period. As a result, forecast models keep the area dry with less
wind with slightly warmer than normal temperatures. However, if
the ridge stays a bit farther to the west, it could mean a cooler
and more unsettled period. For now, though, will stick with the
dry and mild forecast.
Coulston

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  67  48  66  48 /   0   0  20  20
CTB  62  44  61  44 /  20   0  30  30
HLN  66  40  68  46 /  10  10  30  50
BZN  72  41  69  42 /  30  20  20  40
WYS  67  33  60  33 /  20  20  20  40
DLN  69  40  66  43 /  10  10  20  30
HVR  71  47  69  48 /  10   0  10  10
LWT  69  44  66  46 /   0  10  10  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 9 PM MDT this evening Eastern Glacier...
Eastern Pondera...Eastern Teton...Liberty...Northern Rocky
Mountain Front...Southern Rocky Mountain Front...Toole.

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

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

High Wind Warning until 6 PM MDT this evening Blaine...Cascade...
Chouteau...Fergus...Hill...Judith Basin.

Red Flag Warning until 9 PM MDT this evening Central and Eastern
Lewis and Clark National Forest Areas...Chouteau and Fergus
Counties...Helena and Townsend Ranger Districts of the Helena
National Forest...Hill and Blaine Counties.

&&

http://www.weather.gov/greatfalls

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
928 AM MDT THU SEP 24 2020

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

0844 AM     NON-TSTM WND GST 6 NNW SUNBURST          48.96N 111.94W
09/24/2020  M63 MPH          TOOLE              MT   MESONET

            MESONET STATION MTSWT SWEETGRASS (MT DOT).

&&

JAF

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1103 AM MDT THU SEP 24 2020

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

1045 AM     NON-TSTM WND GST 3 SW CUT BANK           48.60N 112.37W
09/24/2020  M55 MPH          GLACIER            MT   ASOS

            ASOS STATION KCTB CUT BANK AIRPORT.

&&

JAF

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1245 PM MDT THU SEP 24 2020

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

1230 PM     NON-TSTM WND GST 3 SW CUT BANK           48.60N 112.38W
09/24/2020  M60 MPH          GLACIER            MT   ASOS

&&