A closed 500 mb low over the Pacific Northwest opened up and shifted toward the Northern Rockies during this period. This wave, in combination with daytime heating, resulted in showers and thunderstorms across the region August 6th.
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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 closed 500 mb low over the Pacific Northwest opened up and shifted toward the Northern Rockies during this period. This wave, in combination with daytime heating, resulted in showers and thunderstorms across the region August 6th. Shear was meager, but was maximized locally to produce one tornado in Jefferson County. Additionally, a landspout was observed in southern Beaverhead County near the Idaho border.
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 6, 1:02 PM MST, 10 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 202 PM MDT Sun Aug 6 2023 .SYNOPSIS... Cool and damp conditions will slowly dissipate across North Central Montana as a weather system slowly moves eastward out of the area. Southwestern Montana has seen a bit of a different day today, as departing clouds have allowed for some sunshine to make an appearance. Expect a drier, but still cloudy and somewhat cool day across the area on Monday, though a few showers and thunderstorms will remain possible. && .DISCUSSION... A slow moving upper level low continues to linger over the area today, resulting in a fairly widespread area of light to moderate rainfall across North Central Montana this afternoon. For the most part, this rainfall is fairly beneficial and slightly unusual for this time of year, when most of our rainfall comes from afternoon and evening thunderstorms, but the mostly gentle nature of the rainfall is allowing it to soak into the ground quite nicely. While we have been concerned about the possibility for heavier thunderstorms to result in some flooding concerns, the widespread rainfall and cloud cover has kept temperatures largely in the 60s across the area, which has really put a chill on the potential for convection and the associated heavier rainfall. While a few isolated areas of heavier rainfall have developed as of early this afternoon, they seem to be moving along fast enough to prevent any sort of flooding at this time. This system will finally exit to the east this evening, which will allow skies to gradually clear up a bit overnight tonight. However, our next weather system will attempt to push into the area Monday and Monday night. Ahead of this system, Monday still looks somewhat cloudy and cool for this time of year, with highs across Southwestern Montana topping out in the low to mid 70s, with highs near 80 across the Plains. Showers and thunderstorms will try to move through Southwestern Montana Monday night as the upper level system moves through, though the current timing of this system will likely make it difficult for showers and storms to reach their full potential. Upper level ridging will build in on Tuesday, which should help kick the showers and storms out of the area by the late afternoon. The next disturbance will move through on Wednesday and Wednesday evening, which will mainly manifest itself with some gusty winds across the plains as it attempts to sweep out some of the lingering moisture across the area, though a few showers and storms may get going across the southwestern mountains. After this system, the upper level flow will be mostly zonal for the second half of the week, with temperatures gradually warming up with drier conditions for the second half of the week. Ludwig && .AVIATION... 1150 AM MDT Sun Aug 6 2023 (06/18Z TAF Period) VFR conditions will prevail across SW MT, including KWYS, KEKS, KBZN, and KHLN as drier air works into the area. A few isolated SHRA and even a TSRA will develop this afternoon, but impacts to any terminals should be brief. Further north, widespread light to moderate rainfall will continue to affect KLWT, KGTF, and even KCTB through this afternoon, bringing MVFR to, at times, IFR conditions due to low clouds and reduced visibility. Skies should clear across all areas overnight, though there will be the potential for some fog to develop overnight tonight. Ludwig Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .HYDROLOGY... Isolated heavy thunderstorms embedded within a broader area of light rain will be possible through this afternoon as a slow moving upper level low remains above the area. While flooding is generally not a major concern, we will have to watch for some areas of minor street flooding should the heavier rain moves over an urbanized area, and burn scars will need to be monitored for increased runoff. Drier conditions are expected on Monday, though an isolated heavier thunderstorm remains possible. Ludwig && .PRELIMINARY POINT TEMPS/POPS... GTF 51 79 53 81 / 50 30 10 20 CTB 48 82 51 82 / 10 20 10 10 HLN 55 80 57 81 / 60 50 40 30 BZN 50 75 51 75 / 60 50 40 40 WYS 39 65 42 63 / 60 70 60 60 DLN 46 71 48 68 / 40 60 50 30 HVR 53 86 54 88 / 10 20 10 10 LWT 49 74 49 78 / 80 40 10 30 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && http://www.weather.gov/greatfalls
The Pocatello radar (KSFX), 176 km away, was scanning. The volume nearest the first event began at 20:12 UTC.
2 tornado. Local standard time, as filed.
Public submitted video of a landspout located northwest of Lime Reservoir, associated with a rain shower in the vicinity.
Emergency manager relayed photos, and several photos were received via social media, of a well documented tornado in the Whitetail Basin. No structural damage occurred and most areas were inaccessible to the NWS storm survey team.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2023Every state in 2023This day in weather historyThe tornado archive for Montana, 2023Warnings 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: 1115329, 1115297.