Wildfire and High Wind in Montana, September 2, 2020

Area Forecast Discussion
National Weather Service Great Falls MT
837 AM MDT Wed Sep 2 2020

.UPDATE...
Forecast remains on track through the weekend with the next front
tracking through the area today, continued warming trend through
the remainder of the week, maybe a shower or two developing along
the passing front along the Hi-Line today, and gusty winds across
much of Northcentral Montana. Only changes made to the forecast
this morning were increasing winds slightly over Fergus and
Judith Basin Counties this afternoon, and including a slight
chance of showers over Hill, Blaine, Chouteau, and Fergus Counties
this afternoon. -TP

&&

.SYNOPSIS...

Warm and dry weather will continue over the next couple of days.
A cold front will push through the area today, bringing with it
gusty winds and an isolated shower along the Hi-Line. Temperatures
will cool off for the overnight tonight, but the warmth will
quickly move back in for the remainder of the week.

&&

.AVIATION...
0530 AM MDT Wed Sep 2 2020 (02/12Z TAF Period)

Mainly VFR conditions will continue over the next 24 hours, but it
will be quite windy again this afternoon and evening. Surface winds
will quickly pick up late this morning and afternoon as mixing
begins, and will result in wind gusts of at least 25-35 kts at most,
if not all, terminals today. LLWS is possible prior to this mix-out,
as winds will quickly increase with height early this morning. While
winds above 5000 feet will generally remain out of the NW the entire
TAF period, low level winds will shift from SW to NW tomorrow
afternoon or evening as a cold front advances from the north. Any
shower activity with this front will be limited to a few isolated
SHRA, mostly along the Hi-Line. Winds will begin to die down quickly
after sunset as the atmosphere stabilizes. -Ludwig

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

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

&&

.FIRE WEATHER...
Low humidity and gusty/strong winds will develop early this morning
over the districts. A wind shift will move southward through the
region this afternoon. Expect west winds to shift to the
northwest/north behind the front. Temperatures will cool and
humidity will increase a bit behind the front. However, warmer air
will quickly move back into the region on Thursday, with a warming
trend expected for Friday and Saturday. Winds could be strong enough
on Saturday, combined with low humidity, that fire highlights might
be necessary for Saturday afternoon. Cooler air, combined with some
mountain snowfall could move into the region on Sunday into Monday.
However, there is still some uncertainty about how cold it will get
by Monday, along with how much precipitation could fall with the
Sun/Mon system. Brusda

&&

.PREV DISCUSSION...
/ISSUED 530 AM MDT Wed Sep 2 2020/

A warm, dry, and breezy day is in store across much of the CWA
today as a cold front approaches the area. Under the pre-frontal
warm advection, winds overnight have maintained some of their
strength from yesterday, which has kept temperatures from falling
too much. Temperatures across the area as of 2AM have struggled
to fall below 60 degrees, and they likely won't fall too much
further unless the winds briefly die down. With temperatures
starting the day warmer than initially expected, high temps for
today have been bumped up slightly across the southern portions of
the CWA.

The aforementioned cold front will begin to push towards the Hi-
Line late this morning or early this afternoon, bringing with it a
wind shift from SW to NW. This wind shift, and accompanying onset
of cold air advection, will likely be the only signal of frontal
passage today, as shower activity along this front will be
isolated, at best. With this, along with the gusty winds
associated with this system, in mind, the Red Flag Warnings will
continue, as any fires that ignite today will have the potential
to spread rapidly (for more on Fire Weather, please see the Fire
Weather Discussion below). The bigger story today will be the
strength of the winds, as winds will reach 20-30 mph with gusts to
40 mph across the plains this afternoon.

Things should begin to quiet down pretty quickly after sunset as
the atmosphere begins to stabilize. With light winds, low
temperatures tomorrow night should drop down into what I'll call
refreshingly cool territory, with most places seeing lows in the
40s to low 50s.

As we move towards the end of the week, upper level ridging will
begin to build back into the area, which will result in
temperatures gradually warming up each day through Saturday. With
an upper level ridge in place, we'll remain dry and mostly clear,
though a few high clouds may begin to push in Saturday night.

Upper level flow should begin to turn more towards the northwest
on Sunday, which should result in a cooler day than Saturday. This
trend should continue into Monday, which will allow for even
cooler air to work into the area for Labor Day. As the upper level
flow continues to shift to the north, a jet streak will move
south from British Columbia into Washington state. This will
allow for an area of enhanced divergence aloft to move near the
area, which will bring us a chance for some needed moisture as it
moves through. Recent model trends have been to strengthen this
system, which would not only increase the likelihood of rainfall,
but would also bring more cold air into the system, which could
result in some snow for the mountain passes. For now, grids have
been made to reflect the possibility for some mountain snow
Monday/Monday night. Upcoming model trends will need to be watched
carefully, as some recent deterministic model guidance has
exhibited some big changes, and a few ensemble suites have also
trended towards a cooler and wetter solution as well. Time will
tell if these trends continue or reverse with the next few model
runs.

In the wake of this trough, upper level ridging will try to build
into the area, but how far east the ridge is able to advance will
likely be influenced by the aforementioned trough. At this time,
it appears that we will gradually warm up through next week, but
there are plenty of details that need to be worked out between now
and then.

Ludwig

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  82  46  83  50 /   0   0   0   0
CTB  76  42  80  46 /  10   0   0   0
HLN  84  49  85  50 /   0   0   0   0
BZN  85  46  85  47 /   0   0   0   0
WYS  77  34  80  35 /   0   0   0   0
DLN  81  46  82  46 /   0   0   0   0
HVR  81  45  80  48 /  10  10   0   0
LWT  81  43  78  48 /   0  10   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 6 PM MDT this evening Central and Eastern
Lewis and Clark National Forest Areas...Chouteau and Fergus
Counties...Eastern Glacier/Toole/Central/Eastern
Pondera/Liberty...Helena and Townsend Ranger Districts of the
Helena National Forest...Hill and Blaine Counties...Lewis and
Clark National Forest Rocky Mountain District-Rocky Mountain
Front...Lincoln Ranger District of the Helena National Forest.

Red Flag Warning until midnight MDT tonight Gallatin National
Forest.

&&

http://www.weather.gov/greatfalls