Excessive Heat in Montana, August 9 to 12, 2018

Name: Excessive Heat in Montana, August 9 to 12, 2018
Start: 2018-08-09T11:00
End: 2018-08-12T17:00
Location: Montana

August 9 to 12, 2018 · NWS GGW · 6 events in 6 counties and zones

A stalled ridge of strong high pressure over the region allowed high temperatures to climb well into the triple digits for many locations for multiple days. Relative humidity values increased enough to make conditions unusually humid.

Where it happened

Every event with a place to put it; 6 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.

Tornadoes
Tropical storms and surge
Floods
Wind
Hail
Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
Other

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The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 6

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 GGW wrote it up.

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 Glasgow, MT wrote its last area forecast discussion before the first event at Aug 9, 2:02 AM MST, 8 hours 58 minutes earlier.

Area forecast discussion, Aug 9, 2:02 AM MST, 8 hours 58 minutes before

Area Forecast Discussion
National Weather Service Glasgow MT
302 AM MDT Thu Aug 9 2018

.DISCUSSION...

Synoptic Setup: A large hot, high pressure heat dome is centered
over the Intermountain West with a ridge reaching up into
Alberta. A large trough runs from well off the coast of northern
California up through the Gulf of Alaska.

Today through Saturday: Ridge will pass over central and eastern
Montana Today through Tomorrow and then stall Saturday. This will
lead to several impacts through these periods.

The first impact will be temperatures reaching near 100 degrees
today and rising each day with increasingly negative health
consequences. For this reason a heat advisory was issued for the
western Most zones today and then spread across the remainder of
the CWA Friday. Have held off issuing a Heat Warning for Saturday
so as to not confuse the message further.

Another potential issue is electricity across the region, as
power lines are often stressed by temperatures above 100 degrees
and any black or brownouts could quickly lead to public health
issues with no AC.

The second impact is smoke that is arriving from British Columbia
and Alberta. This will cause a range of problems including
further health concerns for asthmatics and visibility issues for
aircraft.

The third impact is increasingly low MinRH during the day and
curing of grasses across the region. This has lead to a fire
weather watch for western zones Friday. However, winds will be
limited. So, any easy starts should be put out quickly. Have held
off on a watch for Saturday in order to message Friday first and
because confidence in strong winds for Saturday has dropped as
the front's passage has backed up by nearly 24 hours and this has
also taken the edge off wind speeds.

High temperatures for Saturday are expected to be the highest
through the forecast with some models calling upward of 109. But,
some uncertainty in this solution is built in based on how thick
smoke becomes and whether it blocks out insolation which broad
majority of models do not pick up on. This could lower potential
highs by up to 5 degrees. Therefore have gone with a mid-road
answer of 100 to 106 across the region.

Saturday night through Monday: The front that was expected to
bring relief by Sunday has been delayed and partially diffused.
Therefore, daytime highs for Sunday have risen by about 5 degrees
compared to previous forecasts. Looks like the trough that passes
through is now having trouble bumping the ridge out of the way
but should arrive by Monday.

Monday night onward: confidence in these periods is average with a
less strong ridge redeveloping and gaining influence through
Wednesday night before being flattened out by another questionable
trough in the flow. GAH

&&

.AVIATION...

DENSITY ALTITUDE: Hot temperatures may lead to longer take-offs
in the afternoons through Saturday.

FLIGHT CAT: VFR to MVFR

DISCUSSION: Upper ridging will maintain hot and dry weather
conditions into the Saturday.

SMOKE and HAZE: from fires up in British Columbia and Alberta has
managed to make its way down into northeast Montana and may hang
around generating brief temporary MVFR conditions through
Saturday.

WIND: Light and from the south to southeast this morning. Turning
to the northwest tonight. Then becoming south at 5 to 15 kts
Friday.

Maliawco/GAH

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Friday afternoon through Friday evening
for MTZ134>137.

Heat Advisory from noon today to 9 PM MDT this evening for
Central and Southeast Phillips...Central and Southern Valley...
Garfield...Northern Phillips...Petroleum...Southwest Phillips.

Heat Advisory from 9 AM to 10 PM MDT Friday for Central and
Southeast Phillips...Central and Southern Valley...Daniels...
Dawson...Eastern Roosevelt...Garfield...McCone...Northern
Phillips...Northern Valley...Petroleum...Prairie...Richland...
Sheridan...Southwest Phillips...Western Roosevelt...Wibaux.

&&

weather.gov/glasgow

The radar

The national radar mosaic for the moment the first event began.

Open the radar archive at this moment

Event by event

6 excessive heat. Local standard time, as filed.

Excessive Heat, Western Roosevelt

When: August 9, 11:00 AM MST to August 11, 5:00 PM MST
Where: Western Roosevelt forecast zone
Reported by: ASOS
Coordinates: 48.295, -105.016 (the zone’s center; the record gives no point)

During the afternoon hours of the 9th through the 11th at the Wolf Point airport, high temperatures ranged from 102 to 107 degrees while dew points ranged from the upper 30s to mid 40s. Even though this resulted in relative humidity values dropping to around ten percent, the unusually hot temperatures and stagnant winds added stress to those with heat sensitivities.

Excessive Heat, Garfield

When: August 10, 11:00 AM MST to August 11, 5:00 PM MST
Where: Garfield forecast zone
Reported by: ASOS
Coordinates: 47.278, -106.993 (the zone’s center; the record gives no point)

During the afternoon hours of the 10th and 11th at the Jordan airport, high temperatures ranged from 103 to 105 degrees while dew points ranged from the upper 30s to lower 40s. Even though this resulted in relative humidity values dropping down into the teens, the unusually hot temperatures and stagnant winds added stress to those with heat sensitivities.

Excessive Heat, Central and Southern Valley

When: August 10, 11:00 AM MST to August 11, 5:00 PM MST
Where: Central and Southern Valley forecast zone
Reported by: ASOS
Coordinates: 48.365, -106.667 (the zone’s center; the record gives no point)

During the afternoon hours of the 10th and 11th at the Glasgow airport, high temperatures reached up to 107 degrees while dew points ranged from the mid 30s to mid 40s. Even though this resulted in relative humidity values dropping below ten percent, the unusually hot temperatures and stagnant winds added stress to those with heat sensitivities.

Excessive Heat, Daniels

When: August 10, 11:00 AM MST to August 11, 5:00 PM MST
Where: Daniels forecast zone
Reported by: Mesonet
Coordinates: 48.784, -105.549 (the zone’s center; the record gives no point)

During the afternoon hours of the 10th and 11th at the Scobey airport, high temperatures reached 103 degrees while dew points ranged from the lower 40s to lower 50s. Even though this resulted in relative humidity values dropping down into the teens, the unusually hot temperatures and stagnant winds added stress to those with heat sensitivities.

Excessive Heat, Richland

When: August 11, 11:00 AM MST to August 12, 5:00 PM MST
Where: Richland forecast zone
Reported by: AWOS
Coordinates: 47.788, -104.561 (the zone’s center; the record gives no point)

During the afternoon hours of the 11th and 12th at the Sidney airport, high temperatures reached up to 105 degrees while dew points ranged from the mid 40s to mid 50s. Even though this resulted in relative humidity values dropping down into the teens, the unusually hot temperatures and stagnant winds added stress to those with heat sensitivities.

Excessive Heat, Dawson

When: August 11, 11:00 AM MST to August 12, 5:00 PM MST
Where: Dawson forecast zone
Reported by: AWOS
Coordinates: 47.266, -104.899 (the zone’s center; the record gives no point)

During the afternoon hours of the 11th and 12th at the Glendive airport, high temperatures ranged from 102 to 106 degrees while dew points ranged from the mid 40s to mid 50s. Even though this resulted in relative humidity values dropping down into the teens, the unusually hot temperatures and stagnant winds added stress to those with heat sensitivities.

What these are

Excessive Heat: Heat at or above the local excessive heat warning criteria, or heat that caused deaths.

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

The same day elsewhere

Every storm in Montana in 2018 Every state in 2018 This day in weather history Warnings in Montana, August 2018

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: 777499, 777497, 777498, 777500, 777495, 777496.