Flash Flood and Flooding in South Dakota, July 17 to 18, 2018

Name: Flash Flood and Flooding in South Dakota, July 17 to 18, 2018
Start: 2018-07-17T13:20
End: 2018-07-18T13:00
Location: South Dakota

July 17 to 18, 2018 · NWS UNR · 13 events in 2 counties and zones

A severe thunderstorm developed over the higher elevations of the central Black Hills and tracked east-southeast through the foothills before dissipating over the plains. The storm produced large hail from near Sheridan Lake to Fairburn.

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

Open the live radar over this ground

The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 13

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 UNR wrote it up.

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 Rapid City, SD wrote its last area forecast discussion before the first event at Jul 17, 12:52 PM MST, 28 minutes earlier.

Area forecast discussion, Jul 17, 12:52 PM MST, 28 minutes before

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Hazardous weather outlook, Jul 17, 5:22 AM MST, 7 hours 58 minutes before

Hazardous Weather Outlook
National Weather Service Rapid City SD
622 AM MDT Tue Jul 17 2018

SDZ012-024>031-041-042-072>074-WYZ054>058-071-181300-
Butte-Northern Black Hills-Northern Foot Hills-Rapid City-
Southern Foot Hills-Central Black Hills-Southern Black Hills-
Custer Co Plains-Pennington Co Plains-Fall River-Oglala Lakota-
Sturgis/Piedmont Foot Hills-Southern Meade Co Plains-
Hermosa Foot Hills-Northern Campbell-Southern Campbell-
Western Crook-Wyoming Black Hills-Weston-Northeastern Crook-
622 AM MDT Tue Jul 17 2018

This Hazardous Weather Outlook is for portions of northwestern
South Dakota...southwestern South Dakota...the Black Hills of
South Dakota...northeast Wyoming...and the Black Hills of
Wyoming.

.DAY ONE...Today and Tonight

Scattered thunderstorms are possible late this afternoon through
tonight. Some severe storms are possible, with large hail and
damaging winds the primary threats. Locally heavy rainfall will
also be possible this afternoon and overnight.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

Showers and thunderstorms will persist through Wednesday. Severe
thunderstorms are not anticipated at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed today.

&&

Stay tuned to NOAA weather radio for further updates...or check
our web site at weather.gov/rapidcity

SDZ001-002-013-014-032-043-044-046-047-049-181300-
Harding-Perkins-Northern Meade Co Plains-Ziebach-Haakon-Jackson-
Bennett-Mellette-Todd-Tripp-
622 AM MDT Tue Jul 17 2018 /722 AM CDT Tue Jul 17 2018/

This Hazardous Weather Outlook is for portions of western South
Dakota.

.DAY ONE...Today and Tonight

Scattered showers and thunderstorms are possible tonight. Severe
thunderstorms are not anticipated at this time.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

Showers and thunderstorms will persist on Wednesday. Strong to
severe thunderstorms will be possible across central portions of
South Dakota.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed today.

&&

Stay tuned to NOAA weather radio for further updates...or check
our web site at weather.gov/rapidcity

In the hours before

Special weather statement, Jul 17, 10:50 AM MST, 2 hours 30 minutes before

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Special weather statement, Jul 17, 11:13 AM MST, 2 hours 7 minutes before

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Special weather statement, Jul 17, 11:22 AM MST, 1 hour 58 minutes before

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Special weather statement, Jul 17, 11:35 AM MST, 1 hour 45 minutes before

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Local storm report, Jul 17, 12:26 PM MST, 54 minutes before

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The radar

The Rapid City radar (KUDX), 66 km away, was scanning. The volume nearest the first event began at 20:20 UTC.

Open the radar archive at this moment

Event by event

9 hail, 2 flood, 1 flash flood, 1 thunderstorm wind. Local standard time, as filed.

Hail, Pennington

When: July 17, 1:20 PM MST
Where: Pennington County, 1 mi WSW of Mystic
Measured: 1 in hail
Reported by: Trained Spotter
Coordinates: 44.075, -103.649

Hail, Pennington

When: July 17, 2:10 PM MST
Where: Pennington County, 3.5 mi ENE of Hill City
Measured: 1 in hail
Reported by: Trained Spotter
Coordinates: 43.949, -103.515

Hail, Pennington

When: July 17, 2:16 PM MST
Where: Pennington County, 2 mi ENE of Hill City
Measured: 0.88 in hail
Reported by: Law Enforcement
Coordinates: 43.941, -103.543

Nickel sized hail covered the ground.

Hail, Pennington

When: July 17, 2:22 PM MST
Where: Pennington County, 3 mi ENE of Hill City
Measured: 1.25 in hail
Reported by: Public
Coordinates: 43.947, -103.524

Hail, Pennington

When: July 17, 2:25 PM MST
Where: Pennington County, 1 mi E of Hill City
Measured: 1 in hail
Reported by: Trained Spotter
Coordinates: 43.930, -103.560

Hail covered the ground.

Hail, Pennington

When: July 17, 2:30 PM MST to 2:45 PM MST
Where: Pennington County, 3 mi ESE of Hill City
Measured: 0.88 in hail
Reported by: NWS Employee
Coordinates: 43.913, -103.524

Hail, Pennington

When: July 17, 2:47 PM MST to 2:57 PM MST
Where: Pennington County, 2 mi W of Hayward
Measured: 1.75 in hail
Reported by: Trained Spotter
Coordinates: 43.870, -103.370

Hail to golf ball size covered the ground.

Flash Flood, Pennington

When: July 17, 3:00 PM MST to 5:45 PM MST
Where: Pennington County, 3.41 mi NW of Mt Rushmore to 1.38 mi SW of Mt Rushmore
Cause: Heavy Rain
Reported by: Emergency Manager
Coordinates: 43.920, -103.490

Runoff from heavy rain, exacerbated by hail covered roads, caused flash flooding in and around Keystone. Runoff also caused flooding around Mount Rushmore, where the walking trail was briefly inundated from water rushing down the stairs between the Grandview Terrace and the Sculpture Studio. Water covered Grizzly Gulch Road, parts of Cemetery Road, and several parking lots of businesses along Iron Mountain Road. River levels on Grizzly Bear Creek and Battle Creek quickly rose several feet.

Hail, Custer

When: July 17, 3:29 PM MST
Where: Custer County, 9.98 mi E of Custer
Measured: 1 in hail
Reported by: Park/Forest Service
Coordinates: 43.770, -103.400

Quarter sized hail was reported at the Custer State Park Headquarters office.

Hail, Custer

When: July 17, 3:50 PM MST
Where: Custer County, 2 mi WNW of Fairburn
Measured: 1.5 in hail
Reported by: NWS Employee
Coordinates: 43.701, -103.247

Thunderstorm Wind, Custer

When: July 17, 4:05 PM MST
Where: Custer County, 2 mi WNW of Fairburn
Measured: 52 kt (60 mph) estimated gust
Reported by: NWS Employee
Coordinates: 43.701, -103.247

Wind gusts were estimated at 60 mph.

Flood, Pennington

When: July 17, 5:45 PM MST to July 18, 8:00 AM MST
Where: Pennington County, 3.41 mi NW of Mt Rushmore to 1.38 mi SW of Mt Rushmore
Cause: Heavy Rain
Reported by: Emergency Manager
Coordinates: 43.920, -103.490

Runoff from heavy rain, exacerbated by hail covered roads, continued to cause flooding in and around Keystone. Runoff also caused flooding around Mount Rushmore, where the walking trail was briefly inundated from water rushing down the stairs between the Grandview Terrace and the Sculpture Studio. Water covered Grizzly Gulch Road, parts of Cemetery Road, and several parking lots of businesses along Iron Mountain Road. River levels on Grizzly Bear Creek and Battle Creek quickly rose several feet.

Flood, Custer

When: July 18, 4:00 AM MST to 1:00 PM MST
Where: Custer County, 8.54 mi W of Hermosa to 2.73 mi NW of Fairburn
Cause: Heavy Rain
Reported by: River/Stream Gage
Coordinates: 43.856, -103.360

Minor flooding was observed along Battle Creek and Grace Coolidge Creek upstream of Highway 79. Several pastures and agricultural land were inundated. The river gauge on Battle Creek at Hermosa reached flood stage briefly.

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.
Thunderstorm Wind: Winds from a thunderstorm of 50 knots (58 mph) or more, or lower winds that caused damage or casualties. Measured gusts are marked MG, estimated EG.
Flood: Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.

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

The same day elsewhere

Every storm in South Dakota in 2018 Every state in 2018 This day in weather history Warnings in South Dakota, July 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 2026-10-01. Each event’s entry at NCEI: 765318, 765320, 765321, 765323, 765330, 765332, 765335, 769571, 765336, 765337, 765338, 769574, 769581.