Montana, 2018

Flash Flooding and Hail in Montana, August 23, 2018

August 23, 2018 · NWS GGW · 4 events in 1 county or zone

A slow-moving storm system through southern Montana combined with a moderately unstable atmosphere to produce multiple thunderstorms across eastern Montana during the morning hours of August 23rd. One of these stronger storms became severe and a period of heavy rain lead to flash flooding in Prairie County.

Where it happened

Every event with a place to put it. Tap one for its entry below.

  • Tornadoes
  • Tropical storms and surge
  • Floods
  • Wind
  • Hail
  • Winter weather
  • Heat and drought
  • Cold
  • Fire, smoke and dust
  • Marine and coastal
  • Other

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The toll

Deaths
0
Injuries
0
Property damage
None recorded
Crop damage
None recorded
Events
4

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.

What happened

The episode as NWS GGW wrote it up.

A slow-moving storm system through southern Montana combined with a moderately unstable atmosphere to produce multiple thunderstorms across eastern Montana during the morning hours of August 23rd. One of these stronger storms became severe and a period of heavy rain lead to flash flooding in Prairie County.

What forecasters said that day

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 Glasgow, MT wrote its last area forecast discussion before the first event at Aug 22, 1:02 PM MST, 16 hours 33 minutes earlier.

Area forecast discussion, Aug 22, 1:02 PM MST, 16 hours 33 minutes before
Area Forecast Discussion
National Weather Service Glasgow MT
202 PM MDT Wed Aug 22 2018

.DISCUSSION...

Afternoon Update (2pm MDT): Not much in the way of updating was
necessary today. Cleaning up and increasing some of the winds to
coincide with current trends was the biggest change. Otherwise the
narrative from the morning is still intact.

Bigelbach

PREVIOUS DISCUSSION: Satellite imagery shows very low stratus
across southern Montana, some of which is encroaching into our
CWA. Observations across the southwestern zones show small
dewpoint depressions, and with relatively light winds cannot rule
out the possibility of some patchy fog early this morning, most
likely in the general vicinity of Highway 200 between Winnett and
Jordan. This should be very isolated in nature and not last more
than a couple of hours beyond sunrise.

Today, an upper level low pressure system will move across the
northwestern CONUS and into eastern Montana Thursday. This will
bring a chance of showers and thunderstorms to parts of our area,
most likely south of the Missouri River. In general not much
accumulation is expected, but areas near and south of Glendive may
see a tenth to a quarter of an inch of rain Thursday.

Thursday night through Friday afternoon, the low pressure will
exit the region and a ridge will quickly pass through the area.
This will bring warmer temperatures and drier conditions, and once
again temperatures will approach 90 degrees with relative
humidities in the teens. This, in combination with breezy west to
northwest winds, may bring about enhanced fire weather concerns
Friday. Will continue to monitor this possibility.

Saturday and beyond, a series a ridges and troughs will move
across the region, bringing numerous chances for thunderstorms.
Models are fairly consistent bringing systems across the region
both on Saturday/Sunday and Tuesday, but diverge quite a bit on
exact timing or amounts of any precipitation that may come from
these, so chose to use the latest model blends.

Hickford

&&

.AVIATION...

Expected Flight Category: VFR

Synopsis: Pleasant flying weather continues for the rest of today.
A disturbance will bring isolated to scattered showers, and
perhaps a few thunderstorms, to the southern sites (SDY/GDV)
tomorrow.

Winds: South winds of 10-15 kts will calm to light and variable
for the sites overnight, then turn to the west tomorrow morning
with speeds of 7-12 kts by tomorrow afternoon. Some gusty and
erratic winds can be expected if a thunderstorm moves over any of
the sites.

Bigelbach

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

weather.gov/glasgow

The radar

The Glasgow radar (KGGW), 206 km away, was scanning. The volume nearest the first event began at 12:36 UTC.

Open the radar archive at this moment

Event by event

2 hail, 2 flash flood. Local standard time, as filed.

Hail, Prairie

When
August 23, 5:35 AM MST
Where
Prairie County, 13.12 mi NE of Mildred
Measured
1 in hail
Reported by
Public
Coordinates
46.830, -104.780

Public reported hail up to the size of quarters and heavy rain.

Hail, Prairie

When
August 23, 6:00 AM MST
Where
Prairie County, 10.55 mi NE of Mildred
Measured
1 in hail
Reported by
Public
Coordinates
46.770, -104.770

Public reported quarter size hail.

Flash Flood, Prairie

When
August 23, 8:10 AM MST
Where
Prairie County, 10.09 mi NE of Mildred to 11 mi NE of Mildred
Cause
Heavy Rain
Reported by
Public
Coordinates
46.775, -104.788

Heavy rain began falling at approximately 4:30 AM MST. Public reported water swiftly flowing across Cabin Creek Road and flooding the yard of a home in the area. Total rainfall amount estimated in excess of 4 inches by 9:00 AM MST.

Flash Flood, Prairie

When
August 23, 8:10 AM MST
Where
Prairie County, 10.96 mi ENE of Mildred to 10.77 mi NE of Mildred
Cause
Heavy Rain
Reported by
Public
Coordinates
46.764, -104.754

Public reported water running over a roadway, displacing some of the gravel. Location is on Cabin Creek Road, south of Ash Creek Road. Time estimated by radar.

What these are

Hail
Hail three-quarters of an inch or larger, or smaller hail that caused damage, filed with the largest stone measured.
Flash Flood
Flooding that begins within six hours of the rain that causes it, or of a dam or levee failure or ice jam release, often with deadly speed.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

More

Every storm in Montana in 2018Every state in 2018This day in weather historyWarnings in Montana, August 2018

Sources

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: 768246, 768247, 768253, 768254.