Excessive Heat in Montana, August 9 to 10, 2018

Name: Excessive Heat in Montana, August 9 to 10, 2018
Start: 2018-08-09T12:00
End: 2018-08-10T20:00
Location: Montana

August 9 to 10, 2018 · NWS MSO · 6 events in 6 counties and zones

A ridge of high pressure brought a record breaking heat wave across lower elevations in northwest Montana August 9th and 10th.

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.

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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 MSO wrote it up.

A ridge of high pressure brought a record breaking heat wave across lower elevations in northwest Montana August 9th and 10th.

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 Missoula, MT wrote its last area forecast discussion before the first event at Aug 9, 2:26 AM MST, 9 hours 34 minutes earlier.

Area forecast discussion, Aug 9, 2:26 AM MST, 9 hours 34 minutes before

Area Forecast Discussion
National Weather Service Missoula MT
326 AM MDT Thu Aug 9 2018

...Near Record Heat Today and Friday...

.DISCUSSION...Temperatures today and Friday will be the warmest we
have seen all year across the Northern Rockies. The ridge of high
pressure will continue to build and strengthen over the region
through Friday. The trough of low pressure that was expected to
move through the Northern Rockies Friday, has slowed, and now
looks to move though Saturday afternoon and evening. This will
translate into Friday being the warmest day of the week. Areas
around Orofino, Fenn, and Pierce, Idaho could be flirting with
their all-time record high for August. Due to the expected heat,
the Heat Advisory has been upgraded to an Excessive Heat Warning
in these areas, through Friday. Heat exhaustion will likely occur
during strenuous outdoor activities in this type of hot weather.
A Heat Advisory remains in place for portions of western Montana,
where some locations are expected to reach 100+ degrees.

As mentioned above, a primarily dry cold front will move through
the region during the day on Saturday. This will bring gusty
southwesterly winds up to 30 mph or higher at times Saturday
afternoon and evening. There could be isolated rain showers
and/or thunderstorms across northwestern Montana, but not
expecting a lot of rain out of what does develop. Temperatures
will drop back down to normal for this time of year.

Temperatures will be noticeably cooler for Sunday, though some
leftover breezy winds are likely through the Sunday and Sunday
night period. Much calmer conditions and near normal temperatures
will return for early next week. There is a potential for isolated
showers and thunderstorms to develop during the mid-week over
southwest Montana and Lemhi County, but details on timing are
still uncertain at this time.

&&

.AVIATION...VFR conditions under clear skies are expected in the
next 24 hours, though increased smoke/haze could reduce visibility.
This reduced visibility is most likely over northwest Montana,
and central Idaho. Density altitudes will increase during peak
heating hours.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Fire Weather Watch from Friday afternoon through Saturday
     evening Bitterroot...Deerlodge/West Beaverhead...East
     Beaverhead...East Lolo...Flathead/Glacier Park...Salish and
     Kootenai Reservation.

     Heat Advisory from 3 PM this afternoon to 9 PM MDT Friday
     Flathead/Mission Valleys...Kootenai/Cabinet Region...Lower
     Clark Fork Region...Missoula/Bitterroot Valleys...
     Potomac/Seeley Lake Region...West Glacier Region.

     Fire Weather Watch from Friday afternoon through Saturday
     evening Kootenai...West Lolo.

ID...Excessive Heat Warning until 8 PM PDT Friday Lower Hells
     Canyon/Salmon River Region...Northern Clearwater
     Mountains...Orofino/Grangeville Region.

     Fire Weather Watch from Friday morning through Saturday evening
     Clearwater/Nez Perce...Palouse/Hells Canyon.

&&

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, Lower Clark Fork Region

When: August 9, 12:00 PM MST to August 10, 8:00 PM MST
Where: Lower Clark Fork Region forecast zone
Reported by: COOP Observer
Coordinates: 47.286, -114.685 (the zone’s center; the record gives no point)

Thompson Falls tied an all-time record high of 107 on the 10th and reached 106 on the 9th. The highest two day mean high temperature ever for Thompson Falls occurred on the 9th and the 10th with observations going back to 1956. Superior reached a record high of 105 on the 9th and 107 on the 10th, ranking as the third hottest two day maximum mean temperature stretch with observations going back to 1914. Heron also set a record high of 102 on the 10th. Even though near-record to record high temperatures were observed on the 9th and 10th, overnight temperatures dropped in the mid to upper 50s at night.

Excessive Heat, Kootenai/Cabinet Region

When: August 9, 12:00 PM MST to August 10, 8:00 PM MST
Where: Kootenai/Cabinet Region forecast zone
Reported by: COOP Observer
Coordinates: 48.171, -114.863 (the zone’s center; the record gives no point)

The Libby Dam recorded an all-time high temperature of 108 on the 10th with observations going back to 1986. In addition, a mean two day maximum temperature of 104.5 on the 9th and 10th was the hottest on record. Eureka set all-time record highs of 106 on the 9th and 10th. The maximum two day mean of 106 is 1.5 degrees warmer than the next hottest two day stretch with observations going back to 1960. Troy also set a record high of 106 on the 10th. Even though record or near record highs were observed on the 9th and 10th, overnight lows still dropped into the mid 50s to low 60s.

Excessive Heat, West Glacier Region

When: August 9, 12:00 PM MST to August 10, 8:00 PM MST
Where: West Glacier Region forecast zone
Reported by: COOP Observer
Coordinates: 47.971, -114.069 (the zone’s center; the record gives no point)

West Glacier set an all-time record high of 100 on the August 10th. The two day mean high of 99.5 on the 9th and 10th was the hottest on record going back to 1948. Hungry Horse Dam also set a record high on the 10th of 102. Swan Lake reached 99 on the 9th and set an all-time record high of 106 on the 10th. This two day stretch tied the all-time hottest two day mean maximum temperature stretch with observations going back to 1963. Even with near record to record high temperatures lows were able to drop into the low 50s to upper 50s.

Excessive Heat, Flathead/Mission Valleys

When: August 9, 12:00 PM MST to August 10, 8:00 PM MST
Where: Flathead/Mission Valleys forecast zone
Reported by: COOP Observer
Coordinates: 47.872, -114.424 (the zone’s center; the record gives no point)

Kalispell reached a record high of 100 on August 10th. Creston also record a record high of 98 on August 10th. The Hot Springs RAWS reached 107 and the Jette RAWS reached 103 on the 10th; however, RAWS sites tend to display a warm bias. Low temperatures dropped into the low to mid 50s on the morning of the 10th.

Excessive Heat, Missoula / Bitterroot Valleys

When: August 9, 12:00 PM MST to August 10, 8:00 PM MST
Where: Missoula / Bitterroot Valleys forecast zone
Reported by: ASOS
Coordinates: 46.560, -114.023 (the zone’s center; the record gives no point)

Missoula reached a record high of 104 on the 10th. Hamilton and Stevensville recorded near record highs of 97 on the 10th. Even with record to near record highs on the 10th, overnight lows on the 9th and 10th dropped in the low to mid 50s.

Excessive Heat, Potomac / Seeley Lake Region

When: August 9, 12:00 PM MST to August 10, 8:00 PM MST
Where: Potomac / Seeley Lake Region forecast zone
Reported by: COOP Observer
Coordinates: 46.986, -113.597 (the zone’s center; the record gives no point)

Seeley Lake reached a record high of 98 on the 10th and tied a record high of 95 on the 9th. Potomac also set a record high of 100 on the 10th. Low temperatures on the 10th dropped into the low to mid 40s.

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: 773637, 773639, 773640, 773641, 773642, 773643.