Two episodes of severe weather were observed over this period. The first, on August 18, was related to a ridge breakdown by a strong shortwave.
Every event with a place to put it. 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 TFX wrote it up.
Two episodes of severe weather were observed over this period. The first, on August 18, was related to a ridge breakdown by a strong shortwave. Dry low and mid levels resulted in deep inverted-V profiles, which were conducive to strong wind gusts.
The second episode of severe caliber gusts occurred on August 22nd. Moist southwesterly flow aloft, along with embedded shortwaves resulted in the developments of showers and thunderstorms across Central and Southwest Montana August 22nd. The area just experienced the remnants of Hurricane Hilary, which resulted in relatively moist lower levels, which in turn helped produce ample instability for severe thunderstorms.
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 Aug 18, 12:36 PM MST, 50 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 136 PM MDT Fri Aug 18 2023 .SYNOPSIS... Strong and gusty west winds will continue across the Northern Rockies through the evening hours tonight before a cold front drops south and switches winds to the north. Ahead of this cold front, showers and thunderstorms are possible across Southwest and Central Montana this afternoon and evening, with a few storms potentially becoming severe and producing damaging wind gusts. A period of gusty winds is possible behind this cold front, in addition to a quick drop in temperatures. && .DISCUSSION... Rest of today through tonight...H500 ridge, which has brought very warm temperatures and dry conditions to the Northern Rockies for the past several days, continued to be flattened this afternoon by a potent shortwave through that was sliding east over the Pacific Northwest and Southwestern Canada. This shortwave trough will continue to slide east and over the Northern Rockies and High Plains through the evening and early morning hours on Saturday, resulting in continued strong and gusty west winds across all of Southwest through North Central Montana through approximately 03-06z tonight. These westerly winds have been especially strong so far this afternoon along the Rocky Mountain Front and across western portions of the Hi-Line out to Toole County, with sustained wind speeds of 25- 35 mph and gusts between 50-60 mph being common. In addition to the strong westerly winds, showers and thunderstorms were developing across Western and Southwest Montana early this afternoon, with these showers and storms expected to continue to move east across Southwest through Central Montana prior to 06z this evening. While the best coverage of these showers and thunderstorms is expected to be along and southeast of a Dillon to Bozeman Pass line, shower and storm chances will extend as far north as a Rogers Pass, to Great Falls, to Hays line. A few of the thunderstorms across Central and Southwest Montana this afternoon and early evening could produce damaging wind gusts given the very dry boundary and mid-level air. By the mid-evening hours tonight a strong cold front, which is currently stalled along a line from Calgary to Brooks, Alberta, will begin to advance south and across North Central through Central Montana. This cold front is expected to advance south through areas north of the Montana Highway 200 corridor between 03-06z this evening and north of the I-90 corridor prior to 12z Saturday. This cold front will bring a quick wind shift to the north following its passage, in addition to a 1-3 hour period of gusty winds of between 20-40 mph. Also, temperatures are expected to fall quite quickly behind the passage of the front, with current temperatures across Central and Northern Alberta in wake of the front generally being in the 50s this afternoon. - Moldan Saturday through next Friday...The persistent upper-level ridging remains overhead with flow aloft switching to a more predominate southwesterly flow and reintroducing monsoonal moisture to much of the Treasure State. Additionally, with the west-northwestward propagation of Hurricane Hilary, currently situated south of the southern tip of Baja California, effects of the hurricane will make way toward the Treasure State as early as Sunday. Widespread stratiform precipitation is forecast throughout the weekend as a result, indicative of WPC's marginal risk for excessive rainfall forecast Saturday and Sunday, with a slight risk clipping portions of Southwest Montana for Sunday. Note that excessive rainfall is defined as the risk of rainfall exceeding flash flood guidance with a 25 mile vicinity. Any flooding that may occur as a result of excessive rainfall will generally occur in low- lying areas, in areas of poor drainage, or along small streams and creeks. Probabilistic guidance depicts right around a 60 to 70% chance of locations along the Montana-Idaho border receiving 0.25" Sunday, decreasing to 30 to 50% chance for 0.50" precipitation. Locations generally along and north of the MT Hwy 200 Corridor will see considerably less precipitation during this time. Furthermore, increased cloud coverage (and aforementioned precipitation) as a direct result of the storm will aid in keeping afternoon temperatures 10 to 15 degrees cooler than seasonal averages. Many locations will be in the upper 70s to lower 80s throughout the weekend. Unstable southwesterly winds aloft will persist through much of early next week, leading to daily chances for showers and thunderstorms. Latest blended model guidance continues showing temperatures throughout next week to be near or below seasonal averages for most locations, generally keeping 70s and 80s in the forecast. Cluster Analysis portrays some inconsistencies with regards to the location of the upper-level ridging, though, with some members suggesting the ridge will eventually move eastward and be replaced by a weak upper-level trough. Most cluster members showcase the ridge rebuilding overhead by midweek, which will promote warmer and drier conditions for the remainder of the outlook period. - Pierce && .AVIATION... 1108 AM MDT Fri Aug 18 2023 (18/18Z TAF Period) VFR conditions are primarily expected through 06z Saturday; however, showers and thunderstorms along and southeast of a KHLN to KLWT line may bring temporary periods of MVFR/low-VFR conditions. The bigger concern from any shower or thunderstorm will be the potential for strong and erratic winds, with the potential for isolated wind gusts to approach 50kts. Otherwise, westerly surface winds will continue to strengthen through the early afternoon hours across all of Southwest through North Central Montana, with the strongest winds expected between 20z this afternoon through 02z Saturday. Mountain wave turbulence is possible, especially prior to 06z, in lee of any terrain feature. By 03z Saturday a cold front will begin to advance south from Canada and across the Hi-Line, Central Montana between 06- 09z Saturday, and into Southwest Montana between 09-15z Saturday. This cold front will bring a wind shift to the north, along with lowering CIGS over the plains of Central and North Central Montana. - Moldan Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .FIRE WEATHER... Critical fire weather conditions will continue across all Fire Weather Zones due to a combination of hot, dry, windy, and/or thunderstorm activity through the mid-evening hours tonight. The strong upper level ridge that has brought the hot and dry conditions to the Northern Rockies over the past several days was being flattened by a potent shortwave moving east from the Pacific Northwest and Southwest Canada. As the shortwave slides east and over the Northern Rockies this evening and through the morning hours on Saturday an associated cold front will begin to advance south from Canada. This strong cold front will bring a quick wind shift to the north, in addition to a period of gusty winds of between 20-40 mph. While fire weather concerns will largely decrease in wake of the cold front through Saturday morning due to increasing relative humidity values and decreasing temperatures, a short period of critical conditions may linger this evening given the sudden wind shift across zones 112/113/114/115/117. - Moldan && .PRELIMINARY POINT TEMPS/POPS... GTF 46 72 54 73 / 10 10 30 40 CTB 41 69 48 70 / 10 0 20 30 HLN 53 80 57 75 / 20 20 40 60 BZN 54 82 53 70 / 30 20 50 60 WYS 45 74 47 65 / 20 40 50 80 DLN 49 82 53 67 / 10 30 40 70 HVR 48 75 53 72 / 20 0 40 30 LWT 47 72 50 68 / 30 10 60 50 && .TFX WATCHES/WARNINGS/ADVISORIES... Red Flag Warning until 9 PM MDT this evening for Eastern Glacier/Toole/Central/Eastern Pondera/Liberty. High Wind Warning until 9 PM MDT this evening for Eastern Glacier, Western Toole, and Central Pondera-Northern High Plains. Heat Advisory until 8 PM MDT this evening for Bears Paw Mountains and Southern Blaine-Fergus County below 4500ft- Northern Blaine County. Red Flag Warning until 9 PM MDT this evening for Central and Eastern Lewis and Clark National Forest Areas-Chouteau and Fergus Counties-Hill and Blaine Counties-Lewis and Clark National Forest Rocky Mountain District-Rocky Mountain Front. Red Flag Warning until 9 PM MDT this evening for Helena and Townsend Ranger Districts of the Helena National Forest-Lincoln Ranger District of the Helena National Forest. && http://www.weather.gov/greatfalls
Preliminary Local Storm Report
National Weather Service Great Falls MT
150 PM MDT Fri Aug 18 2023
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1121 AM Non-Tstm Wnd Gst 8 SE East Glacier Park 48.36N 113.11W
08/18/2023 M57 MPH Glacier MT Mesonet
Mesonet station DCRM8 Deep Creek RAWS.
&&
MoldanPreliminary Local Storm Report
National Weather Service Great Falls MT
151 PM MDT Fri Aug 18 2023
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1112 AM Non-Tstm Wnd Gst 3 SW Cut Bank 48.60N 112.37W
08/18/2023 M52 MPH Glacier MT ASOS
ASOS station KCTB Cut Bank Airport.
&&
MoldanThe Billings radar (KBLX), 171 km away, was scanning. The volume nearest the first event began at 20:25 UTC.
11 thunderstorm wind. Local standard time, as filed.
Mesonet station MTBZH Bozeman Pass measured a severe caliber wind gust.
Measured via an Ambient Weather sensor near Winston (19MWL).
ASOS station KHLN Helena Airport measured a severe caliber gust behind the main line of thunderstorms.
RAWS station GINM8 Ginger measured a peak wind gust of 58 mph. The station reports hourly so the time of the gust was estimated using radar.
Measured by military AWOS site k1cm Charlie.
Measured via military AWOS site K1nm November.
Measured by MT Department of Transportation site Bowmans Corner.
Measured via military AWOS station K1GM Golf.
Measured by site EW1931 Rudyard.
A 40 x 60 metal shed destroyed from collapsing thunderstorm wind gusts. Nearby observations recorded wind gusts in excess of 70 mph.
ASOS station KCTB Cut Bank Airport measured a severe caliber gust.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2023Every state in 2023This day in weather historyWarnings in Montana, August 2023
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: 1129849, 1129848, 1129850, 1129851, 1115281, 1115292, 1115252, 1115254, 1115264, 1133998, 1129852.