A weak upper level disturbance pushed across North Central Montana with relatively strong upper-level winds. Adequate dynamic ascent lead to the development of widespread showers and thunderstorms with damaging wind gusts.
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The episode as NWS TFX wrote it up.
A weak upper level disturbance pushed across North Central Montana with relatively strong upper-level winds. Adequate dynamic ascent lead to the development of widespread showers and thunderstorms with damaging wind gusts.
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 11, 4:00 AM MST, 1 hour 46 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 500 AM MDT Fri Aug 11 2017 Updated Aviation Discussion .SYNOPSIS... An approaching disturbance across southern Canada will introduce the potential for isolated showers and thunderstorms across the region this afternoon and evening. By the weekend, we begin to see a shift in the weather pattern with the next storm system approaching the region from the west. Showers and thunderstorms will be possible Saturday and Sunday evening, with the better chance of widespread showers and storms Sunday afternoon and evening. Unsettled weather may extend into the early part of next week with temperatures remaining near-average through the time period. .DISCUSSION... Today through Sunday... Latest water vapor satellite imagery across the region this morning illustrates a rather well-defined shortwave trough across parts of southern Saskatchewan and Alberta. This shortwave is progressing southward along a persistent northwesterly flow aloft across the state. At the surface, high-resolution model data suggests ongoing showers and thunderstorms for northern and eastern areas of the CWA this morning, with the potential for further development this afternoon and evening. Additionally, elevated thunderstorms look possible across the Rocky Mountain Front due to a developing surface upslope flow. Conditions turn tranquil overnight tonight as the shortwave trough exits the area. Saturday should be mainly dry areawide with the exception of more isolated elevated thunderstorms along the higher terrain of the Rocky Mountain Front. The next storm system approaches our area from the west Sunday afternoon and evening which will aid in the development of widespread showers and storms for central and western areas. Impacts from these storms include the potential for strong gusty winds in any stronger storm and brief heavy downpours. Dangerous lightning will also pose a risk for new fire starts due to ongoing drought conditions. KLG Sunday night through Friday... Look for ongoing convective activity into the night on Sunday with widespread showers, and a few strong thunderstorms across most central and northern areas of the CWA. Latest model guidance suggests the pattern to remain rather unsettled into the day on Monday with showers and storms to continue, mainly for central and southwestern areas of the state. We return to a zonal upper level flow pattern by mid-week and into late in the week with only a limited chance of seeing a spotty shower or two. Temperatures will maintain rather seasonal through this time period with no sign of any extreme heat in the foreseeable future KLG && .AVIATION... Updated 1100z. A potent disturbance will push a front south across the plains and into central and southwest Montana by this evening. This will bring -SHRA and -TSRA beginning this morning to the Hi-Line (including KCTB and KHVR) and then extending south through the rest of the terminals through the remainder of the afternoon and evening hours. Expect VFR conditions except for MVFR or IFR in the heaviest showers/storms. The primary impact from the storms will be gusty and erratic winds, with frequent lightning also a threat. Area wildfires will continue to filter in smoke and haze across the region through the period, generally affecting terminals along and south of a KHLN to KBZN line. Some slight reductions of visibility to around 6SM at times will be possible due to these hazy conditions. Moldan/CC && .FIRE WEATHER... Continued northwest flow along with a weather front will bring slightly higher RH values. Unstable conditions will keep chances for afternoon and evening showers and thunderstorms...with the main threats again being gusty winds and lightning. Saturday looks to see warming temperatures with lowering RH. A few thunderstorms are also possible...mainly along the Rocky Mountain Front and the southwest. There are indications a pattern shift is possible Sunday into early next week. This may bring increased westerly winds with some scattered showers and thunderstorms. Anglin/CC && .PRELIMINARY POINT TEMPS/POPS... GTF 81 52 85 54 / 20 20 10 10 CTB 79 51 84 51 / 20 20 10 10 HLN 85 56 88 56 / 20 20 10 10 BZN 84 52 85 51 / 20 20 10 10 WEY 73 42 77 40 / 30 30 20 20 DLN 82 50 84 51 / 20 20 10 10 HVR 81 53 85 54 / 30 20 10 0 LWT 80 52 81 51 / 30 20 10 0 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && weather.gov/greatfalls
The Missoula radar (KMSX), 100 km away, was scanning. The volume nearest the first event began at 12:46 UTC.
1 thunderstorm wind. Local standard time, as filed.
Mesonet Station TT010 reported a 63 mph wind gust from a thunderstorm.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2017Every state in 2017This day in weather historyWarnings in Montana, August 2017
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: 716477.