On Wednesday May 19, 2021, an upper level Pacific trough dove south through the Pacific Northwest into the Great Basin and then became nearly stationary for a couple of days. The southerly flow ahead of this system transported middle and upper level moisture into the state, while an upslope east to northeast flow developed at the lower levels in response to relatively strong surface high and low…
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.
On Wednesday May 19, 2021, an upper level Pacific trough dove south through the Pacific Northwest into the Great Basin and then became nearly stationary for a couple of days. The southerly flow ahead of this system transported middle and upper level moisture into the state, while an upslope east to northeast flow developed at the lower levels in response to relatively strong surface high and low pressure systems respectively set up over Alberta Canada and Utah. The upslope flow eventually led to cold air damming and the development of a low level barrier jet along the Divide. This resulted in strong northerly surface winds along eastern slopes adjacent to the Rocky Mountain Front for periods of near blizzard conditions and subsequently sent the unseasonably cold air into the southwestern portion of the state. Locations from Roger’s Pass northward into the East Glacier and Browning areas observed the worst conditions due to the combination of falling snow and gusty northerly winds. The impacts ranged from severe driving conditions on area roadways to isolated power outages. By Thursday morning, the rain began to change to snow at lower elevations over North-central Montana and this transition eventually reached the southwest valleys later that evening.
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 19, 10:50 PM MST, 1 hour 10 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 1150 PM MDT Wed May 19 2021 ... Aviation section updated... .SYNOPSIS... A slow moving spring storm will continue to impact the region through Friday. Rain and snow increase in coverage tonight, with accumulating snow likely along the Rocky Mountain Front and the adjacent plains. Daytime temperatures for Thursday and Friday will mostly be in the 30s and 40s, with nighttime lows near and below freezing. It will be slightly drier and warmer for the weekend, but the cool and unsettled pattern is expected to persist. && .UPDATE... The evening update has been published. The biggest change was to upgrade southern Lewis and Clark County to a Winter Storm Warning, primarily for locations along and northwest of the highway 200 road segment that runs from Bowman's corner to Roger's Pass. Snow has already began to accumulate on the road surfaces near Roger's Pass and moderate to at times heavy snowfall can be expected through the night. Snow levels were also lowered for areas northwest of a Great Falls to Havre line, which added some light accumulation tonight into Thursday morning for these areas. Tonight's low temperatures were for this area as well. -RCG && .AVIATION... 1150 PM MDT Wed May 19 2021 (20/06Z TAF period) Rain and snow continue to push into Southwest and North-Central Montana this evening, bringing poor visibility and low ceilings with it. VFR/MVFR conditions are expected to continue at KEKS, KBZN, and KWYS through the overnight, but KEKS and KBZN will see ceilings lower to IFR levels tomorrow morning. Further north, while KLWT and KHVR will continue to see VFR/MVFR conditions through the morning, other terminals will see more consistent IFR/LIFR conditions continue into tomorrow as rain and snow continue, along with low ceilings. Ludwig Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PREV DISCUSSION... /ISSUED 612 PM MDT Wed May 19 2021/ Remainder of this afternoon through Friday...A strong Pacific low pressure system is now moving southeastward through Washington and is now pumping in upper level moisture from the southwest, while an easterly upslope flow develops in the lower atmosphere. Rain and snow has already begun along the Divide, with the latest MDT camera images from Roger's Pass showing light snow accumulation on grassy surfaces. This activity will continue to increase and expand eastward as the evening progresses. The heaviest QPF still favors the western half of Central/North- central Montana and along the Divide, with more scattered and lighter totals expected further east. Locations along the Rocky Mountain Front and the adjacent eastern slopes/lower elevations will see a good set up for periods of moderate to heavy snow due to the moisture rich easterly upslope winds and H700 temperatures dropping to the -10 to 12C range by early Thursday. Ensemble guidance continues to zero in on this area for the heaviest snowfall, especially for areas from Roger's Pass northward to East Glacier and Browning. Warm surface temperatures may hold back road surface accumulation, but the potential for slippery roads and reduced visibility will increase during the heavier bands of snow later tonight into Thursday morning. In addition to that, trees and power lines will likely see faster accumulation, especially given the wet nature of the snow. Power outages will be a concern, as well as hypothermia for newborn livestock and those recreating in the backcountry. The only change to the current winter weather highlights was to delay the Winter Weather Advisory for Eastern Glacier County from 9 pm tonight to 3 am Thursday morning. During the day on Thursday, moisture and colder air expands eastward, though snow accumulation will be slowed down by daytime heating. High temperatures will mostly be in the 30s for Central/north- central locations, with only slightly warmer readings in the southwest. Another round of light accumulating snow can be expected Thursday night into early Friday. It will likely be more widespread due to the colder temperatures, with the best chances for impacts mostly along and northwest of a Butte to Havre line (and the central mountains). Another cold and raw day can be expected again for Friday as rain and snow continues through the evening hours, though the winter weather highlights will likely be allowed to expire Friday morning due to the onset of diurnal heating. -RCG Saturday Through Next Wednesday...Closed upper level low centered over the Great Basin slowly moves out to the northeast this weekend, bringing additional rounds of precipitation to the area until the low finally lifts out northeast of the area early next week. There is broad model consensus on a relatively drier period on Saturday before another round of widespread precipitation develops Sunday as a disturbance rotates north through the area ahead of the upper low. Models have trended wetter with this feature but still show some differences with the strength and exact track of the surface low and mid level shortwave features. Better chances for significant precipitation amounts with this feature will exist across eastern portions of the forecast area as the wave tracks north through eastern MT. Some model solutions show a fairly deep surface low and slower progression of the system north into Canada Sunday night into Monday. Threat for snow with additional precipitation will mainly be limited to the highest mountain elevations as warmer air aloft wraps back north into the region, though daily temperatures at the surface only warm slowly and remain well below seasonal averages through Sunday. A trend back to more seasonable temperatures is expected next week though additional disturbances look to move through the area bringing some additional precipitation chances. Hoenisch && .PRELIMINARY POINT TEMPS/POPS... GTF 34 37 29 35 / 100 90 90 80 CTB 29 33 27 35 / 100 100 90 80 HLN 35 41 32 38 / 100 90 90 80 BZN 40 49 32 42 / 70 80 80 70 WYS 35 56 32 51 / 60 60 70 90 DLN 38 47 30 41 / 70 60 80 90 HVR 36 40 30 39 / 60 100 90 80 LWT 39 40 28 36 / 60 60 100 80 && .TFX WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 3 AM Thursday to 9 AM MDT Friday Eastern Glacier...Eastern Pondera...Eastern Teton...Liberty... Toole. Winter Storm Warning until 9 AM MDT Friday Northern Rocky Mountain Front...Southern Rocky Mountain Front. Winter Weather Advisory until 9 AM MDT Friday Cascade... Jefferson...Judith Basin. Winter Storm Warning until 9 AM MDT Friday Central and Southern Lewis and Clark. && http://www.weather.gov/greatfalls
11 winter storm, 8 heavy snow. Local standard time, as filed.
Military ASOS Foxtrot station K1FM observed visibility ranging from 1/4 SM to 1 SM in snow and wind for much of the am hours and early afternoon.
Snow and slush packed roads and reduced visibility create dangerous driving conditions on highway 200 near Roger's Pass.
Northwest Energy reports scattered power outages due to snow and wind near the Bowman's Corner area.
Northwest Energy reported power outages reported in the Chouteau area due to snow and winds.
Northwest Energy reported power outages throughout Cascade County, including the Great Falls area due to snow and wind. Snowfall amount totals up to 3 inches were observed in the area.
Northwest Energy reported as many as 323 units without power in Fairfield area due to snow and wind. Snowfall amounts up to 5 inches observed in the Fairfield area.
Severe driving conditions reported on HW 89 from HW 44 to Two Medicine Bridge due to snow and wind.
Snowfall amounts of 12 inches reported near Heart Butte. Reduced visibility and flickering electricity was also reported.
A snowfall total of 18 inches reported near Roger's Pass.
A snowfall total of 15 inches recorded at the Heart Butte SOTEL (24 W Bynum).
Snowfall total of 14 inches observed over 48 hr period at 2 W Helena.
Trained spotter at 7 ENE Manhattan reported snowfall total of 9 inches.
Severe driving conditions due to wind and snow were reported on MT Highway 3 MP 0 to 23 due to snow and wind.
A snowfall total of 12 inches reported at 9 SSW Havre.
Trained spotter reported snowfall total of 11.5 inches, most of which fell in a two hour period.
Trained spotter at 7 SE Rocky Boy reported a 14 inch snow total.
A 10.5 inch snow total was reported at 6 NE Craig.
A 10.5 inch snow total was reported at 6 NE Craig.
Trained spotter at 2 SE Montana City reported a 12.3 snowfall total.
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: 963233, 963218, 963219, 963222, 963225, 963227, 963239, 963241, 963220, 963221, 963247, 963250, 963242, 963256, 963254, 963266, 963269, 963270, 963262.