On August 19th, weak instability combined with a subtle disturbance and attendant cold front to provide sufficient dynamics for isolated thunderstorm development across Central and Southwest Montana. One thunderstorm near Forest Grove in Fergus County produced quarter sized hail.
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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.
On August 19th, weak instability combined with a subtle disturbance and attendant cold front to provide sufficient dynamics for isolated thunderstorm development across Central and Southwest Montana. One thunderstorm near Forest Grove in Fergus County produced quarter sized hail.
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 19, 6:01 PM MST, 1 hour 14 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 701 PM MDT Mon Aug 19 2019 .UPDATE... Have made a quick update to the current forecast to reflect the isolated thunderstorms that have developed over the higher terrain of Central Montana this evening, from Helena east to Lewistown. Am not expecting much from these storms, just some wind gusts to 30 mph, isolated lightning strikes, and some brief light rainfall. Am thinking that the gusty winds are worthy of mention in the forecast, so have done so. These storms will likely continue to diminish from the west through 10 pm or so. Coulston && .SYNOPSIS... A strengthening high pressure ridge over the interior western United States will bring additional warming and drying through Wednesday as temperatures warm to above average levels. A frontal system will move through the region Wednesday night and Thursday bringing at least a small chance for showers and thunderstorms Wednesday night followed by breezy and cooler conditions Thursday. && .AVIATION... Updated 658 PM MDT Mon Aug 19 2019 (20/00Z TAFs) VFR conditions are expected to continue through at least the next 24 hours as a high pressure ridge continues to build into the area. Scattered mid level cloudiness will move across the area through 04Z or so. A showers and thunderstorms have developed over portions of Central and Southwest Montana (mainly KHLN to KLWT) and they will likely linger through around 04Z or so as well. It is unlikely that showers/storms will directly impact the terminals in Southwest Montana (KBZN KEKS KWYS). Skies will be mostly clear after 04Z as the airmass stabilizes. However, the airmass will destabilize again after 18Z, bringing another chance of showers/thunderstorms to Southwest Montana. Breezy easterly winds will also develop during the afternoon. Coulston && .FIRE WEATHER... Warm and dry conditions today will moderate slightly on Tuesday as an airmass from the north moves into the region. Hot and dry condtions return on Wednesday as the upper level ridge moves across the region with potential for breezy south winds Wednesday afternoon. A frontal system then moves east across the area Wednesday night bringing a shift to west winds with breezy to windy conditions developing during the Wednesday overnight period and continuing through Thursday. A few showers and thunderstorms are possible with the frontal passage Wednesday evening and again Thursday in the more moist but somewhat unstable airmass that follows. Hoenisch && .PREV DISCUSSION... /ISSUED 525 PM MDT Mon Aug 19 2019/ Tonight through Tuesday night...Surface high pressure and a slightly cooler airmass from north of the border will slip south across the area this evening in response to a deepening thermal trough of low pressure over the Great Basin. This will bring a shift in winds to the north and northeast overnight and easterly by Tuesday morning. The slightly cooler airmass will also temporarily keep temperatures from rising additionally on Tuesday. Cannot rule out the development of an isolated thunderstorm across SW MT late this afternoon and again Tuesday afternoon, but moisture is very limited with some low level instability capped by subsidence aloft under the building upper ridge. Hoenisch Wednesday through Next Monday...The ridge amplitude appears to peak on Wednesday, which should be the warmest day of the week for most locations. Highs are expected to be mostly in the 90s. Breezy winds with a southerly component combined with RH values in the low 20s may create some fire weather concerns in regard to the curing of fuels on Wednesday afternoon. A trough of low pressure is then progged to approach the northern Rockies Wednesday night into early Thursday and eventually sweep east through the rest of the state. The attendant cold front will bring a chance for a few showers and thunderstorms late Wednesday into Thursday along with about a 10 degree drop in Thursday's high temperatures as compared to the day prior. Westerly flow then develops in the mid and upper levels for the remainder of the forecast period with temperatures near normal and mostly dry conditions. && .PRELIMINARY POINT TEMPS/POPS... GTF 51 86 56 91 / 0 0 0 0 CTB 47 83 52 90 / 0 0 0 0 HLN 53 90 55 92 / 20 0 10 10 BZN 50 92 52 92 / 10 0 0 0 WEY 41 87 43 87 / 10 0 0 0 DLN 49 89 51 88 / 0 0 0 0 HVR 52 86 55 92 / 0 0 0 0 LWT 51 82 54 87 / 20 0 0 0 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && http://www.weather.gov/greatfalls
Special Weather Statement
National Weather Service Great Falls MT
803 PM MDT Mon Aug 19 2019
MTZ050-200230-
Judith Basin-
803 PM MDT Mon Aug 19 2019
...A STRONG THUNDERSTORM WILL AFFECT SOUTHEASTERN JUDITH BASIN AND
SOUTHWESTERN FERGUS COUNTIES...
At 803 PM MDT, a strong thunderstorm was located 16 miles southwest
of Hobson, or 16 miles south of Stanford, moving east at 35 mph.
Brief heavy rain, winds in excess of 30 mph, and half inch hail are
possible with this storm.
Locations impacted include...
Hobson, Ackley Lake State Park, Sapphire Village and Utica.
If outdoors, consider seeking shelter inside a building.
This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.
LAT...LON 4689 10978 4686 10980 4683 10980 4682 10984
4679 10979 4681 11030 4699 11031 4704 10975
4690 10976
TIME...MOT...LOC 0203Z 267DEG 30KT 4691 11019
SCSpecial Weather Statement National Weather Service Great Falls MT 805 PM MDT Mon Aug 19 2019 MTZ051-200230- Fergus- 805 PM MDT Mon Aug 19 2019 ...A STRONG THUNDERSTORM WILL AFFECT SOUTHEASTERN FERGUS COUNTY... At 804 PM MDT, a strong thunderstorm was located near Lewistown, moving east at 40 mph. Brief heavy rain, winds in excess of 30 mph and pea size hail are possible with this storm. Locations impacted include... Lewistown, Grass Range, Heath and Forestgrove. If outdoors, consider seeking shelter inside a building. This storm may intensify, so be certain to monitor local radio stations and available television stations for additional information and possible warnings from the National Weather Service. LAT...LON 4691 10941 4709 10943 4716 10877 4689 10874 TIME...MOT...LOC 0204Z 266DEG 34KT 4701 10931 SC
The Billings radar (KBLX), 136 km away, was scanning. The volume nearest the first event began at 02:15 UTC.
1 hail. Local standard time, as filed.
A trained spotter stated that the hail size started out as marble sized but then increased to the size of quarters (1 inch diameter). Hail was covering the ground at the time of the report.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2019Every state in 2019This day in weather historyWarnings in Montana, August 2019
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: 852521.