Recent melting snow in the northeast corner of Montana and points eastward provided extra moisture near the surface. Cold overnight temperatures and a clear overnight sky allowed for fog to develop mainly over the lower lying areas near and east of MT Highway 13.
Every event with a place to put it; 3 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.
Recent melting snow in the northeast corner of Montana and points eastward provided extra moisture near the surface. Cold overnight temperatures and a clear overnight sky allowed for fog to develop mainly over the lower lying areas near and east of MT Highway 13.
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 Mar 5, 2:11 AM MST, 1 hour 49 minutes earlier.
Area Forecast Discussion National Weather Service Glasgow MT 211 AM MST Fri Mar 5 2021 .DISCUSSION... Some fog is developing early this morning in the NE corner of the state. Meanwhile, the fog has increased in coverage in nearby areas of North Dakota and Saskatchewan. Several short term models have this fog spreading into most of Sheridan and Eastern Roosevelt Counties and becoming dense before sunrise this morning. Parts of Daniels and Richland Counties will also see fog. Will maintain the Dense Fog Advisory for Sheridan and Eastern Roosevelt until 10 am this morning. Upper ridge will bring warm and dry weather to the area today and Saturday with well above normal temperatures. The ridge moves to the east Saturday afternoon as a shortwave trough brings a dry cold front through the area Saturday Night. Sunday will be breezy and cooler with west winds. High pressure moves through the area Sunday Night and Monday with dry weather continuing. Flow aloft turns to the SW Monday Night and Tuesday as ridge moves to the east and upper trough digs on the Pacific Coast. This will bring a cold front through the area Monday Night with a chance of light rain and light snow that will continue on Tuesday. Models have diminished the amount of precipitation with this system in recent runs. Cooler temperatures are expected the remainder of next week with mainly dry weather. && .AVIATION... LAST UPDATED: 0900Z FLIGHT CAT: VFR - MVFR early then VFR remainder of today and tonight. FOG: Dense fog is looking more and more likely north of the terminals with KSDY and KOLF being on the edges of the deck. These two sites will need to be monitored if the coverage for fog expands beyond where its currently predicted to stop. DISCUSSION: Elsewhere, high pressure remains prevalent over the region, with pleasant flying weather expected for the next couple of days. WIND: Light and variable in most areas this morning and east around 10 knots at KGGW. South winds 5 to 10 knots will develop this afternoon and become south to SE tonight. && .GLASGOW WATCHES/WARNINGS/ADVISORIES... Dense Fog Advisory until 10 AM MST this morning for Eastern Roosevelt...Sheridan. && weather.gov/glasgow
The national radar mosaic for the moment the first event began.
3 dense fog. Local standard time, as filed.
At the US-2 @Stateline DOT site (MTSTA), the web cam showed visibility dropped to a quarter mile or less for about 3 1/2 hours on the morning of the 5th. Times are estimated.
At the Navajo MT-5 DOT site (MTRED), the web cam showed visibility dropped to a quarter mile or less for about 3 hours on the morning of the 5th. Times are estimated.
At the Plentywood airport mesonet site (KPWD), visibility dropped to a quarter mile or less from early to mid morning on the 5th. Dense fog was also observed at the Comertown Turn-Off MT-5 DOT site (MTCOM) until 10:00 AM.
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, March 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 2026-09-24. Each event’s entry at NCEI: 948340, 948341, 948339.