Wildfire in Montana, August 17 to 31, 2020

Area Forecast Discussion
National Weather Service Great Falls MT
1120 AM MDT Mon Aug 17 2020

Aviation Section Updated.

.UPDATE...

A weak shortwave trough crossed the Northern Rockies this morning,
producing isolated, high-based light rain showers west of the
Continental Divide. Moisture and mid-level clouds associated with
this activity are now spreading across North-central Montana. The
morning KTFX sounding reveals a deeply mixed dry adiabatic layer.
Cloud cover is slowing the rate of heating, but given our location
under the ridge axis and drier air return behind this wave, there
is not enough confidence to lower today's forecast high
temperatures. Even if realized highs today end up a few degrees
below forecast, they will still be near calendar record highs and
continue to warrant a heat advisory. The passing shortwave has
resulted in a higher mid-level westerly winds. Downward mixing of
momentum from these winds is expected to produce periods of gusty
west winds this afternoon, generally 10-20 mph, with gusts to 30
mph possible. With this change to higher winds today and another
day of very low relative humidity, critical fire weather
conditions are expected to develop by early afternoon across much
of North-central Montana. Thus, the most significant change with
this morning update was to add a Red Flag Warning in effect for
today. Additional fire weather concerns related to possible
dry/wet thunderstorms over southwest Montana may yet warrant
new fire weather highlights for tomorrow.

&&

.SYNOPSIS...

High pressure aloft will continue to bring very hot conditions to
the forecast area today with most locations seeing high
temperatures of 95 to 105. Isolated to possibly scattered
thunderstorms are expected today and Tuesday but only minor rain
amounts of a trace to a few hundreths of an inch are anticipated.

&&

.AVIATION...

1120 AM MDT Mon Aug 17 2020 (17/18Z TAF Period)

VFR conditions prevail. Scattered to at times broken upper-level
clouds are expected through the period. Approaches and departures to
terminals could experience turbulence due to deep layer mixing
westerly breezes within a very warm airmass. Isolated to scattered
high-based thunderstorms will likely develop over southwest Montana
this afternoon and evening. Some haze and smoke from wildfires could
reduce visibility in southwest Montana, especially in the valleys
near the Bear Creak Fire southwest of KDLN.

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...

Strong upper level ridging will persist over the region through
mid-week, which will result in afternoon high temperatures in the 90s
to near 105 degrees today with only slightly cooler temperatures
on Tuesday. Relative humidity will be in the teens today and
Tuesday with breezy winds approaching 20 mph at times. On Tuesday
winds speeds will begin to increase as a disturbance moves across
the ridge, with Fire Weather Zone 112 possibly seeing gusts
approaching 30 mph or more. As such, the Fire Weather Watch for
zone 112 will remain in effect. Monsoon moisture aloft will bring
a risk for isolated to scattered afternoon and evening
thunderstorms each day with some storms expected to be dry.

&&

.CLIMATE...

Record high temperatures will be in danger of being broken today
and Tuesday as values rise into the 90s to near 105 degrees.
Today will have the best chance of seeing record highs with
current record values at most locations in the mid- to upper 90s.

Here is a list of the current record highs for Monday/Tuesday for
select climate sites:

Cut Bank (93/95), Havre (99/105), Great Falls (98/101), Lewistown
(98/97), Helena (98/100), Bozeman (96/98), and Dillon (95/94).

&&

.PREV DISCUSSION...
/ISSUED 550 AM MDT Mon Aug 17 2020/

A strong upper level ridge will remain over the region today and
Tuesday for very hot conditions that could set multiple records.
Monsoon moisture aloft will continue to move northward along the
western boundary of the upper ridge and will bring an increasing
chance for very light showers and dry thunderstorms. With
temperatures expected to top out at 95 to 105 today, have issued a
Heat Advisory for North Central Montana through Tuesday evening.
The Helena area has also been included in a Heat Advisory for
today but conditions should be slightly cooler on Tuesday so this
advisory will end this evening.

Wednesday through next Monday...Shortwave energy will continue to
rotate around the high pressure system as it is flattened by
troughing over the eastern Pacific. This will increase
thunderstorm activity for Wednesday and Thursday, mostly for
Southwest Montana. Still expecting a slight increase in west to
northwest breezes but confidence in widespread elevated winds has
decreased a bit over the last 24 hours. Regardless, conditions for
fire weather will continue to be monitored. Slightly cooler
temperatures can be expected as a result of passing shortwaves and
a the flattening of the high pressure system, with highs falling
back to the upper 80s to middle 90s for Wednesday and a few
degrees lower for Thursday. The ridge looks to build back for the
weekend, though it may be displaced to the east by Pacific
Northwest troughing. This would create a southwesterly flow aloft
for our region and keep lower elevation temperatures mostly in the
upper 80s to lower 90s, with a continued chance for afternoon and
evening thunderstorms.
- RCG

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  99  64  96  63 /  10  10  10  20
CTB  96  60  94  61 /  10  10  10  10
HLN  99  64  94  62 /  20  20  20  40
BZN  98  58  94  58 /  20  20  10  20
WYS  90  46  88  47 /  10  20  30  30
DLN  94  56  90  56 /  10  20  30  20
HVR 100  62  99  64 /  10  10   0  20
LWT  97  62  94  61 /  10  10  10  20

&&

.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...Eastern Glacier/Toole/Central/Eastern
Pondera/Liberty...Hill and Blaine Counties...Lewis and Clark
National Forest Rocky Mountain District-Rocky Mountain Front.

Fire Weather Watch from Tuesday afternoon through Tuesday
evening Eastern Glacier/Toole/Central/Eastern Pondera/Liberty.

Heat Advisory until 9 PM MDT Tuesday Blaine...Cascade...
Chouteau...Eastern Glacier...Eastern Pondera...Eastern Teton...
Fergus...Hill...Judith Basin...Liberty...Toole.

Heat Advisory until 9 PM MDT this evening Central and Southern
Lewis and Clark.

&&

http://www.weather.gov/greatfalls