An approaching trough and associated modest mid/upper jet supported the development of isolated severe thunderstorms in southwest Montana.
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The episode as NWS TFX wrote it up.
An approaching trough and associated modest mid/upper jet supported the development of isolated severe thunderstorms in southwest Montana.
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 24, 9:49 PM MST, 3 hours 11 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 1049 PM MDT Thu Aug 24 2017 ...Update to Aviation... .SYNOPSIS... Showers and a few thunderstorms will continue to move through Southwest Montana overnight, mainly from Lincoln south. For Friday and into the first half of next week, expect mostly dry conditions along with a warming trend. By the middle portion of next week...afternoon highs will average close to 15 degrees above normal. && .UPDATE... The initial band of showers/storms associated with a SFC trough/cold front continues to push into eastern Montana at this time. Meanwhile, the main trough axis still lies to our west and is proceeded by a modest mid/upper jet. This jet appears to be what is providing enough lift to sustain thunderstorm activity from west of Helena south to the MT/ID border. This jet will push east and weaken tonight, but should still allow thunderstorms to impact parts of SW MT through about 1-3am or so. For this reason, I upped pops from Helena to Bozeman and points south. Latest obs/radar trends suggest gusty winds and perhaps some hail will remain possible, but the threat of strong storms should decrease as instability continues to wane overnight. Across central MT, I kept a low-end chance of showers in as the above-mentioned jet may glance that area with enough lift to generate a few showers (mainly southern sections of central MT). MARTIN && .AVIATION... Updated 0449Z. Another upper level disturbance has triggered isolated/scattered showers and thunderstorms mainly south of a KMSO-KGTF-KGGW line. Light rain, occasional lightning strikes and gusty winds can be expected from these storms through 09Z or so. Partly to mostly cloudy conditions and widespread VFR conditions anticipated on Friday. Another round of isolated/scattered thunderstorms develops over the southern half of the forecast area after 20Z Friday and continues through about 03Z Saturday. Areas of smoke also continue to reduce visibility to MVFR conditions at times through the forecast period. mpj && .FIRE WEATHER... An upper level disturbance will keep a risk of showers and isolated thunderstorms going overnight, mainly Southwest Montana. Gusty winds and occasional lightning continue to remain the main threat with any stronger storm or collapsing shower/storm. It will be a bit cooler on Friday with storms exiting the eastern and southern portions of the region. For Saturday into early next week...it will be mostly dry...warmer along with low humidity. Isolated thunderstorms are possible mid next week. Brusda/MARTIN && .PREV DISCUSSION... /ISSUED 540 PM MDT Thu Aug 24 2017/ Tonight through Saturday...Showers and thunderstorms continue to push northward through the region, as an upper level trof and weak Pacific cool front move through the region. The shower activity might be more widespread than previously thought...but rainfall amounts are still quite light. Most areas are receiving less than 0.05 inches...with a few areas around 0.10 to 0.15 inches. Most of the storms will diminish by 10 PM or so...but a few storms will linger into Friday...especially east/south of Great Falls. Afternoon highs will be slightly cooler on Friday...but dry and warmer conditions return to the region on Saturday...as an upper level ridge starts to rebuild over the region. Brusda Saturday night through Thursday...The strong high pressure ridge will remain over the southwest U.S. through this period. This ridge will extend into Montana for the remainder of the weekend into early next week, which will keep the forecast area dry and afternoon temperatures well above normal. However, a series of weak shortwave troughs are forecast to eject from a larger upper level low pressure trough off the Pacific coast and help break down the ridge during the middle of the week. The forecast models differ on just how strong these shortwaves will be, but they do agree on a more westerly flow aloft over the area. As a result, I have focused the chance for showers/thunderstorms over the mountains, with only a few showers/thunderstorms sporadically moving over the plains. Would like to see better agreement before being more specific with timing of convective activity. However, this more westerly flow aloft will cause temperatures to cool a bit closer to normal for late August by next Thursday. Coulston/Brusda && .PRELIMINARY POINT TEMPS/POPS... GTF 54 81 51 84 / 20 0 0 0 CTB 49 77 44 82 / 0 0 0 0 HLN 56 83 53 87 / 50 10 20 0 BZN 51 84 49 85 / 50 20 30 0 WEY 45 74 39 77 / 40 40 30 0 DLN 50 82 48 84 / 50 10 10 0 HVR 55 81 51 86 / 20 0 10 0 LWT 55 80 51 83 / 50 20 30 0 && .TFX WATCHES/WARNINGS/ADVISORIES... Red Flag Warning until midnight MDT tonight Deerlodge/Western Beaverhead National Forest. && weather.gov/greatfalls
Special Weather Statement National Weather Service Great Falls MT 1144 PM MDT Thu Aug 24 2017 MTZ015-053>055-250900- Madison-Broadwater-Meagher-Gallatin- Including the cities of Harrison, Pony, Waterloo, Cameron, Ennis, Jeffers, McAllister, Toston, Townsend, Winston, Martinsdale, Checkerboard, Ringling, White Sulphur Springs, Bozeman, and Gallatin Gateway 1144 PM MDT Thu Aug 24 2017 ...Thunderstorms to bring frequent lightning across southern Montana early tonight... A line of thunderstorms from Townsend to east of Ennis and west of Big Sky area are currently producing frequent lightning. These storms will continue to produce lightning as they move east tonight...along with gusty winds up to 40 MPH. Isolated brief heavy rain and small hail is possible...although thunderstorms will be mainly dry. Those outdoors should seek shelter. New fire starts are also possible to areas with extreme fire danger conditions.
The Billings radar (KBLX), 174 km away, was scanning. The volume nearest the first event began at 07:58 UTC.
1 thunderstorm wind. Local standard time, as filed.
Mesonet station BBAS, Bridger Bowl - Base reported a measured wind gust of 59 mph.
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: 716719.