Strong southerly flow associated with the remnants of Hurricane Hilary overspread much of Southwest Montana August 21st. Although plenty of gusts greater than 50 mph were observed, no High Wind Warning caliber gusts were observed.
Every event with a place to put it; 1 filed by county or forecast zone are drawn at its center, in a lighter ring. 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.
Strong southerly flow associated with the remnants of Hurricane Hilary overspread much of Southwest Montana August 21st. Although plenty of gusts greater than 50 mph were observed, no High Wind Warning caliber gusts were observed. The lone verification point was from high sustained winds at Norris Hill on the northern end of the Madison River Valley zone.
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 21, 12:42 PM MST, 3 hours 30 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 142 PM MDT Mon Aug 21 2023 .SYNOPSIS... Gusty winds across Southwest Montana will continue through the early overnight period. Rain will continue in spots, primarily across western portions of North-central Montana through tonight. Temperatures begin a rebound back closer to normal the next couple days with chances for showers and a few thunderstorms across the region in the afternoon and evening. && .DISCUSSION... Through tonight... The remnants of Hilary continue to shift northward toward the region this afternoon. The first concern is for gusty winds across Southwest Montana, especially at ridgetops and in north south oriented valleys. Forecast H700 flow is on the order of 40-55 kts, which overall is a trend down from previous model guidance, but should still be sufficient for a few instances of strong winds and gusts. Winds have been a bit slow to pick up but as of writing, two stations were gusting into the 50-55 mph range near the Idaho border in Beaverhead county. Hence, the High Wind Warnings will remain in effect through 3 AM tonight. The second concern will be for rain, especially across the East Glacier Park region. High resolution models give a greater than 70% chance for an inch of rain from Browning north to the international border and points westward in Glacier County. 1 and 3 hour flash flood guidance is largely greater than 2 inches, which is on the high side considering expected precipitation. Regardless, areas in steep terrain in Glacier National Park and on/below burn scars will be at risk for localized flash flooding, rock and mud slides, in addition to debris flow if rain is persistent over any one area. -AM Tuesday through the end of the week... As we head into the middle of this week, our upper level flow will remain out of the southwest as a massive upper level ridge remains parked over the Central CONUS, which will allow mild and somewhat moist air to continue to work through the area. With the moisture around, we will see a few showers and thunderstorms pop up each afternoon through Thursday, but overall expect things to quiet down quickly after the moisture from Hilary exits the area Tuesday morning. Beyond Thursday, a piece of the ridge over the Central CONUS will begin to work into the region, which will help to shut off the chances for showers and thunderstorms for the most part, in addition to causing us to return to warmer temperatures by early next week. Ludwig && .AVIATION... 1123 AM MDT Mon Aug 21 2023 (21/18Z TAF Period) The main concerns for this TAF period will be for lowered vis/cigs in areas of rain, mainly across Central and North-central Montana, and gusty southerly to southwesterly winds across Southwest Montana through tonight. Mountains will be obscured, especially across Central and North-central Montana. -AM Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .HYDROLOGY... Moisture from the remnants of Tropical Storm Hilary will continue work through the region today, resulting in mostly light rainfall across the region today. Most of the area will rainfall totals coming in around a tenth of an inch of less, though areas in and around Glacier National Park have a greater than 70% chance for seeing an inch or more. Although flash flood guidance is relatively high, the risk of flash flooding and rock/mud slides and debris flow in terrain has warranted a Flood Watch for the Northern Rocky Mountain Front and adjacent high plains through tonight. Ludwig/-AM && .PRELIMINARY POINT TEMPS/POPS... GTF 57 86 57 83 / 20 20 50 10 CTB 54 78 52 76 / 90 30 40 10 HLN 62 88 58 85 / 10 30 40 20 BZN 58 84 54 83 / 10 10 10 10 WYS 47 68 44 70 / 30 40 30 20 DLN 55 77 50 77 / 10 10 10 10 HVR 58 85 56 85 / 50 10 40 10 LWT 61 85 55 82 / 20 10 20 20 && .TFX WATCHES/WARNINGS/ADVISORIES... Flood Watch through late tonight for East Glacier Park Region- Northern High Plains. High Wind Warning until 3 AM MDT Tuesday for Beaverhead and Western Madison below 6000ft-Gallatin and Madison County Mountains and Centennial Mountains-Madison River Valley-Ruby Mountains and Southern Beaverhead Mountains. && http://www.weather.gov/greatfalls
Preliminary Local Storm Report
National Weather Service Great Falls MT
1232 PM MDT Mon Aug 21 2023
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1030 PM Debris Flow 11 NNW Silver Star 45.83N 112.36W
08/20/2023 Jefferson MT Emergency Mngr
Jefferson County DES reported MT Highway 2 W
was closed for awhile Sunday evening due to
a rock slide caused by rainfall.
&&Preliminary Local Storm Report
National Weather Service Great Falls MT
252 PM MDT Mon Aug 21 2023
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0700 AM Rain 2 ENE Norris 45.58N 111.65W
08/21/2023 M1.26 inch Madison MT Cocorahs
Cocorahs station MT-MD-12 2 ENE Norris. The
period of the Rain event was 24 hours.
0343 PM Rain 22 SW Cameron 44.95N 111.96W
08/20/2023 M1.25 inch Madison MT Mesonet
Mesonet station BTKM8 Burnt Creek RAWS. The
period of the Rain event was 24 hours.
0800 AM Rain 5 SSE Grant 44.94N 113.03W
08/21/2023 M1.18 inch Beaverhead MT CO-OP Observer
CO-OP Observer station GRNM8 Dillon 26 SSW.
The period of the Rain event was 24 hours.
0705 AM Rain 1 NW Big Sky 45.27N 111.34W
08/21/2023 M1.14 inch Gallatin MT Cocorahs
Cocorahs station MT-GN-21 Big Sky 1.7 NW.
The period of the Rain event was 24 hours.
0605 PM Rain 21 SW Lima 44.47N 112.95W
08/20/2023 M1.14 inch Beaverhead MT Mesonet
Mesonet station HRKM8 Harkness RAWS. The
period of the Rain event was 24 hours.
0259 PM Rain 4 NE Lima 44.69N 112.54W
08/20/2023 M1.12 inch Beaverhead MT Mesonet
Mesonet station LMRM8 Antelope RAWS. The
period of the Rain event was 24 hours.
0316 PM Rain 3 SSW Ennis 45.30N 111.75W
08/20/2023 M1.09 inch Madison MT Mesonet
Mesonet station ENNM8 Ennis RAWS. The period
of the Rain event was 24 hours.
0621 AM Rain West Yellowstone 44.67N 111.10W
08/21/2023 M0.97 inch Gallatin MT Cocorahs
Cocorahs station MT-GN-24 West Yellowstone
0.4 NNE. The period of the Rain event was 24
hours.
0700 AM Rain Glen 45.48N 112.69W
08/21/2023 M0.97 inch Beaverhead MT Cocorahs
Cocorahs station MT-BV-22 Glen CoCoRaHS. The
period of the Rain event was 24 hours.
0800 AM Rain 10 NE Dillon 45.32N 112.49W
08/21/2023 M0.95 inch Beaverhead MT Cocorahs
Cocorahs station MT-BV-8 10 NE Dillon
CoCoRaHS. The period of the Rain event was
24 hours.
0645 PM Rain 12 NNE Raynolds Pass 44.87N 111.34W
08/20/2023 M0.94 inch Gallatin MT Mesonet
Mesonet station HBDM8 18.0 NW West
Yellowstone. The period of the Rain event
was 24 hours.
0316 PM Rain 1 ESE Wise River 45.79N 112.94W
08/20/2023 M0.94 inch Beaverhead MT Mesonet
Mesonet station WRSM8 Wise River. The period
of the Rain event was 24 hours.
0255 PM Rain 16 ENE Belgrade 45.88N 110.89W
08/20/2023 M0.93 inch Gallatin MT Mesonet
Mesonet station TR369 Gnf West
Zone-Portable. The period of the Rain event
was 24 hours.
&&Preliminary Local Storm Report
National Weather Service Great Falls MT
253 PM MDT Mon Aug 21 2023
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1200 PM Non-Tstm Wnd Gst 6 WSW Big Sky 45.23N 111.45W
08/21/2023 M57 MPH Madison MT Mesonet
Mesonet station YCTIM Yellowstone Club -
Avalanche.
0159 PM Non-Tstm Wnd Gst 4 NE Lima 44.69N 112.54W
08/21/2023 M57 MPH Beaverhead MT Mesonet
Mesonet station LMRM8 Antelope RAWS.
1205 PM Non-Tstm Wnd Gst 21 SW Lima 44.47N 112.95W
08/21/2023 M56 MPH Beaverhead MT Mesonet
Mesonet station HRKM8 Harkness RAWS.
0227 PM Non-Tstm Wnd Gst 4 NNE Mcallister 45.50N 111.70W
08/21/2023 M54 MPH Madison MT Mesonet
Mesonet station MTNOR Norris Hill (MT DOT).
&&The national radar mosaic for the moment the first event began.
1 high wind. Local standard time, as filed.
Mesonet station Norris Hill MTNOR measured sustained winds, averaged over an hour, of 42 mph. The sensor also measured a peak gust of 55 mph.
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: 1129846.