A passing Pacific trough and attendant cold front brought strong surface winds to the Northern Rocky Mountain Front and adjacent plains. Cold air advection combined with 40 kt + H700 winds allowed surface gusts to exceed 50 kts.
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 TFX wrote it up.
A passing Pacific trough and attendant cold front brought strong surface winds to the Northern Rocky Mountain Front and adjacent plains. Cold air advection combined with 40 kt + H700 winds allowed surface gusts to exceed 50 kts.
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 Great Falls, MT wrote its last area forecast discussion before the first event at May 28, 8:04 AM MST, 1 hour 40 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 904 AM MDT Fri May 28 2021 .UPDATE... Surface pressure is rising over Northwest Montana as the incoming Pacific Front begins to cross the Continental Divide. The frontal position is not well defined, but nonetheless will result in a period of strong winds for the rest of today. The forecast describes these changes well enough, but minor adjustments were posted to better match observed trends in temperatures, RH, and winds. && .SYNOPSIS... Today, expect strong winds, with some mountain showers possible across the Continental Divide, and a chance of isolated thunderstorm activity across parts of east-central Montana and parts of the southwest. For this Memorial Day Weekend, expect warming temperatures and mostly dry conditions with periods of breezy to gusty winds. && .AVIATION... 540 AM MDT Thu May 27 2021 (28/12Z TAF period) VFR conditions prevail throughout this TAF period at all airfields except KWYS, where I have included a PROB30 2821/2823 4SM -SHRA. Additionally, the mountains of the Continental Divide and southwest Montana will be obscured, at times. Expect widespread strong gusty winds, today, with high winds forecast across The Northern and Southern Rocky Mountain Front, East Glacier and Toole Counties until 28/22Z. As an upper level trof passes through the area, any moisture that falls is likely to evaporate in the strong gusty winds, falling as virga. Additionally, There is a slight chance to a chance for isolated thunderstorm activity to occur this afternoon/evening across the mountains of far southeast Beaverhead County, southern Madison County, portions of Gallatin County and northeastward to Fergus County. - Fogleman Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PREV DISCUSSION... /ISSUED 540 AM MDT Fri May 28 2021/ Today... A strong upper level ridge exits eastern Montana and enters The Dakotas, behind the ridge, a closed upper level area of lower heights is located over The Canadian Northwest Territories, with the associated upper level trof extending through northeastern Washington State and further south-southwestward across central/eastern Oregon. A tight cross-barrier flow develops across The Rocky Mountain Front, with The Polar Front Jet (PFJ) located overhead northwest/north-central Montana. Strong gusty winds develop, with high winds expected to occur across areas of The Northern and Southern Rocky Mountain Front, as well as, East Glacier and Toole Counties. Please, see the issued High Wind Warning for details. The instability and exhaust associated with this trof, along with some moisture advection into area, favors a slight chance to a chance for isolated thunderstorm activity to occur across the mountains of far southeast Beaverhead County, southern Madison County, portions of Gallatin County and northeastward to Fergus County. Additionally, some precipitation is forecast along areas of The Divide. Outside of The High Wind Warning area, widespread strong gusty winds are expected. Any moisture that passes through these winds is expected to evaporate, resulting in said moisture falling as virga above the valleys and plains. As a result, little to no moisture is expected to reach the low level surface with this event. Saturday through next Friday... As the trof moves across the region on Saturday, there is a slight chance for a few isolated thunderstorms to occur across northeast-central Montana during the Saturday afternoon/evening time period. by Saturday evening, the next upper level ridge builds into the area. An upper level trof develops off the coast of northern California and over-time deepens and lingers over western Mexico. This allows ridging to build into Montana, and to dominate the upper level pattern across The Treasure State into Thursday. A warming trend begins. Saturday's highs are forecast to reach generally into the 60s, and by Wednesday, highs range in the mid to upper-80s. For this forecast period, expect mostly light winds, with periods of breezy to gusty winds, and mostly dry conditions with plenty of sunshine. As of this time, there is a slight chance of isolated thunderstorm activity, Thursday afternoon and evening. We will continue to monitor and update the forecast as necessary. Next Friday looks to be another warm and dry day, with widespread breezy to gusty winds. Some considerations that we will be following, closely, include the fact that the coming warming trend will cause melting of the mountain snowpack. This will likely cause the rivers to rise; so, we will closely monitor river response. Additionally, rivers will begin to run faster; therefore, those recreating on rivers will need to take care to prepare for faster running waters. Finally, even with the recent moisture added to our area, as temperatures warm and Relative Humidity (RH) values drop, and with periods of gusty winds and possible thunderstorm activity, fire weather will remain a focus for us, as we progress through this forecast period. - Fogleman && .PRELIMINARY POINT TEMPS/POPS... GTF 61 36 65 38 / 0 0 10 0 CTB 56 37 64 37 / 10 10 0 0 HLN 63 38 68 41 / 0 0 0 0 BZN 66 32 65 35 / 20 0 0 0 WYS 63 25 62 26 / 30 10 0 0 DLN 65 31 64 36 / 0 0 0 0 HVR 64 40 67 41 / 0 10 10 0 LWT 61 35 62 36 / 30 0 10 0 && .TFX WATCHES/WARNINGS/ADVISORIES... High Wind Warning until 4 PM MDT this afternoon Eastern Glacier...Northern Rocky Mountain Front...Toole. && http://www.weather.gov/greatfalls
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1022 AM MDT FRI MAY 28 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0940 AM NON-TSTM WND GST 2 SE BROWNING 48.54N 112.98W
05/28/2021 M58 MPH GLACIER MT MESONET
MESONET STATION MTBWG BROWNING (MT DOT).
&&4 high wind. Local standard time, as filed.
MDOT station 2 SE Browning observed a 54 kt (62 mph) non-thunderstorm wind gust.
KCTB measured an average wind speed of 36 kt (41 mph) from 1225 pm to 135 pm MST.
MDOT Two Medicine Bridge station measured a 50 kt (58 mph) non-thunderstorm wind gust.
KCTB observes a 52 kt (60 mph) non-thunderstorm wind gust.
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, May 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: 963307, 963312, 963314, 963309.