A cold upper level system moved south out of Canada into western Montana, bringing extremely cold temperatures and strong north to northeast winds. This resulted in dangerous wind chills, as low as 39 below zero.
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.
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.
The episode as NWS MSO wrote it up.
A cold upper level system moved south out of Canada into western Montana, bringing extremely cold temperatures and strong north to northeast winds. This resulted in dangerous wind chills, as low as 39 below zero.
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 Dec 5, 5:04 PM MST, 2 hours 56 minutes earlier.
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</html>The national radar mosaic for the moment the first event began.
6 extreme cold/wind chill. Local standard time, as filed.
A spotter 10 ENE of Arlee reported wind chills down to 21 below zero.
Wind chills down to 34 below zero were reported in Essex.
Observation site in Avon reported wind chills down to 39 below zero.
An observation site in Greenough reported wind chills down to 21 below zero.
Missoula ASOS reported wind chills down to 20 to 22 below zero.
RAWS/SNOTELs reported wind chills as low as 23 below zero.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2009Every state in 2009This day in weather historyWarnings in Montana, December 2009
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 2026-10-01. Each event’s entry at NCEI: 203882, 203884, 203889, 203890, 203887, 203888.