Moisture trapped near the surface for many days and a benign weather pattern combined with suddenly clearing skies and colder temperatures, which allowed dense freezing fog to form over many locations in northeast Montana.
Every event with a place to put it; 5 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 GGW wrote it up.
Moisture trapped near the surface for many days and a benign weather pattern combined with suddenly clearing skies and colder temperatures, which allowed dense freezing fog to form over many locations in northeast Montana.
The national radar mosaic for the moment the first event began.
5 dense fog. Local standard time, as filed.
At the Malta airport AWOS site (KM75), visibility of a quarter mile or less was recorded for about 8 hours from the afternoon of the 8th into the early morning of the 9th, then again for 2 hours on the morning of the 10th.
At the Sidney airport ASOS site (KSDY), visibility of a quarter mile or less was recorded for about 1 1/2 hours in the evening on the 8th.
At the Culbertson airport mesonet site, visibility of a quarter mile or less was intermittent - for 2 1/4 hours on the night of the 8th, then again for 1 hour in the early morning on the 9th.
At multiple locations near the Missouri River valley of western Roosevelt County, visibility of a quarter mile or less was recorded from the night of the 8th through the early morning of the 9th.
At the Glasgow airport ASOS site (KGGW), visibility of a quarter mile or less was recorded intermittently through the early and mid-morning hours on the 9th.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2021Every state in 2021This day in weather historyWarnings in Montana, January 2021
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: 937293, 937286, 937287, 937290, 937292.