Wildfire in Montana, September 4 to 30, 2020

Name: Wildfire in Montana, September 4 to 30, 2020
Start: 2020-09-04T14:00
End: 2020-09-30T23:59
Location: Montana

September 4 to 30, 2020 · NWS TFX · 1 event in 1 county or zone

The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 1

Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.

What happened

The episode as NWS TFX wrote it up.

Weak shortwave troughs interacted with lingering monsoon moisture and sufficient diurnal heating set the conditions for thunderstorm development over potions of Central and Southwest Montana on Wednesday and Thursday (Aug 26th, 27th). This was followed by a short period of much cooler wetter weather for the final weekend in August as a potent longwave trough dived southeast from the Gulf of Alaska. This short lived cool down ended when high pressure ridging returned to the region in early September and weak shortwaves provided periods of windy but warm and dry conditions. This sequence of meteorological occurrences created a set up for a lightning hold over fire in the foothills northeast of Bozeman to become the significant Bridger Foothills Wildfire.

What forecasters said that day

The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Great Falls, MT wrote its last area forecast discussion before the first event at Sep 4, 1:55 PM MST, 5 minutes earlier.

Area forecast discussion, Sep 4, 1:55 PM MST, 5 minutes before

Area Forecast Discussion
National Weather Service Great Falls MT
255 PM MDT Fri Sep 4 2020

.SYNOPSIS...

Near record warm and dry conditions continue into the first half
of this weekend before a change to much cooler weather occurs
Sunday and Monday. Windy and dry conditions on Saturday will lead
to critical fire weather concerns before cooler temperatures
arrive Sunday. Widespread precipitation is likely Sunday and
Monday with snow possible at higher elevations.

&&

.DISCUSSION...

Skies are clear across the western U.S. while remaining under
the influence of a strong upper level ridge. Expect an
unseasonably mild night as this warm air mass remains over the
region. The ridge begins to flatten on Saturday with an
approaching shortwave trough arriving in the increasing westerly
flow. A lee-side trough develops, which will produce stronger
downslope winds. This combined with deep layer mixing will produce
wind gusts of 25 to 40 mph on Saturday. Red Flag warnings are now
in effect to highlight the expected critical fire weather
conditions. The surface low moves away to the east Saturday
evening, but a robust pressure gradient and strong northwest winds
aloft could maintain at least elevated fire weather conditions
late into Saturday night, and yet another unseasonably mild night.
A few locations may set daily record high temperatures.

Conditions begin to change for North-central Montana as a strong
surface cold front arrives Sunday morning. Timing of the frontal
passage will determine daily high temperatures Sunday. The front
will take some time to progress through central and then southwest
Montana, so these areas are likely to experience one more warm and
dry day up until the front moves through. Elevated or critical
fire weather conditions may develop on Sunday, so a Fire Weather
Watch remains in effect until confidence in timing the front can
be improved with further evaluation.

Sunday night through Tuesday Morning...Strong upper level trough and
an associated Canadian cold front move through the region Sunday
night through Tuesday. Latest forecast models continue to support
widespread precipitation over the forecast area with wetting rains
expected at lower elevations and accumulating snow in the mountains.
Coldest temperatures are expected Monday night with forecast
overnight lows dipping down to near or below freezing in many areas.
These temperatures will be highly dependent on cloud cover and it is
possible that any residual showers could produce light snowfall or
at least a mix of rain and snow even at lower elevations. Confidence
remains high on timing and impact for the approaching system and
cooling temperatures. However, confidence in precipitation type,
location, and amounts continues to be fairly low but should increase
as the weekend progresses.

Tuesday through next Friday...A strong upper level ridge ridge along
the West Coast will gradually move inland as the cold weather system
exits the region before stalling out over the Great Basin. North to
northwesterly flow aloft prevails over Montana during this time
frame with atmospheric thickness values gradually increasing and
bringing a return to warmer temperature with mostly dry conditions.
-Fogleman/mpj

&&

.AVIATION...

1140 AM MDT FRI SEP 4 2020 (04/18Z TAF PERIOD)

VFR conditions prevail across the region under a dry NW to W flow
aloft as an upper level ridge of high pressure moves over the
Northern Rockies and MT. Surface winds remain fairly light through
this evening before increasing from the west late tonight through
Saturday morning. Widespread gusty winds return late Saturday
morning through Saturday evening. -TP

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...

Temperatures remain well above seasonal averages through Saturday
with afternoon humidity falling below 15% in some areas as very
dry air aloft moves over the region. Winds increase on Saturday
with gusts from the west around 25-35 mph expected across much of
central and southwest MT, becoming northwesterly late Saturday
afternoon and evening. Humidity and winds may be slow to improve
Saturday night before winds shift to northerly by Sunday morning
across areas from Great Falls east to Lewistown and north. Areas
from Helena to While Sulphur Springs and south could still see
warm and breezy conditions on Sunday before the cooler airmass
spreads south through those areas. Much cooler conditions develop
late Sunday night into Monday with increasing confidence in the
development of widespread wetting precipitation. Hoenisch

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  54  93  53  75 /   0   0   0  10
CTB  51  89  50  66 /   0   0   0  30
HLN  54  94  52  82 /   0   0   0   0
BZN  52  97  49  84 /   0   0   0   0
WYS  35  87  39  81 /   0   0   0   0
DLN  51  92  47  82 /   0   0   0   0
HVR  51  95  51  70 /   0   0   0  20
LWT  54  93  53  73 /   0   0   0  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon Saturday to midnight MDT Saturday
night 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.

Fire Weather Watch from late Saturday night through Sunday
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 from 1 PM to 10 PM MDT Saturday
Deerlodge/Western Beaverhead National Forest...Eastern
Beaverhead National Forest.

Red Flag Warning from noon Saturday to midnight MDT Sunday night
Gallatin National Forest.

&&

http://www.weather.gov/greatfalls

Event by event

1 wildfire. Local standard time, as filed.

Wildfire, Gallatin

When: September 4, 2:00 PM MST to September 30, 11:59 PM MST
Where: Gallatin forecast zone
Reported by: Other Federal Agency

A lightning hold out fire was discovered in the foothills northeast of Bozeman when dry conditions began to feed its growth. the fire was initially only able to grow to about 400 acres but then exploded to 7000 acres the next day as red flag conditions moved into the region. At one point, the fire was classified as a type 1 incident and eventually grew to 8224 acres. The fire persisted through mid- October and destroyed 68 structures, including 30 residential homes. It caused damage to 11 structures, of which five were residences. The containment cost was $7.225 million.

What these are

Wildfire: A fire burning in wildland vegetation, with its acreage and damage where known.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in Montana in 2020 Every state in 2020 This day in weather history Warnings in Montana, September 2020

Sources

NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 922744.