Overview
On the afternoon of July 17th, 2018, thunderstorms developed over the Black Hills. Some of these storms became severe, producing large hail and damaging winds. However, the main issue with these storms was a significant amount of small hail, covering the roads and making travel difficult. Snow plows were needed to clear inches of hail from the roads. Additionally, heavy rain caused flash flooding, which was exacerbated by hail-covered roads. The storms over the Black Hills eventually moved southeast onto the plains. More thunderstorms moved into northeastern Wyoming, becoming severe and producing large hail and strong winds. Heavy rain with these storms also produced flash flooding. These storms merged to form one storm system (what meteorologists call a mesoscale convective system, or MCS), and spread into South Dakota.
Hail:
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| Between Twin Springs and Pink Cabin Road (Dave Maudlin) |
Twin Springs Road (Dave Maudlin) |
Old Hill City Road (Dave Maudlin) |
Old Hill City Road (Dave Maudlin) |
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 |
 |
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| Old Hill City Road (Dave Maudlin) |
Old Hill City Road (Dave Maudlin) |
Near Fairbun (Sara Chamberlain) |
Near Fairburn (Sara Chamberlain) |
Flooding
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 |
 |
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| Storm Total Precipitation | Grizzly Bear Creek near Keystone | Thompson Creek, near the WY/MT border (John Pierce) |
Thompson Creek, near the WY/MT border (John Pierce) |
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 |
 |
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| Thompson Creek, near the WY/MT border (John Pierce) |
Thompson Creek, near the WY/MT border (John Pierce) |
Thompson Creek, near the WY/MT border (John Pierce) |
Thompson Creek, near the WY/MT border (John Pierce) |
Radar:
Storm Reports
The storm reports listed below are in descending order and may not
necessarily be the final storm reports.
Hail reports listed by size (inches)
SIZE LOCATION ST COUNTY TIME
------ ----------------------- -- -------------- -------
1.75 2 W HAYWARD SD PENNINGTON 0355 PM
GROUND COVERED IN HAIL.
1.50 2 WNW FAIRBURN SD CUSTER 0450 PM
1.25 SHARPS CORNER SD OGLALA LAKOTA 0600 PM
3-4 INCHES OF WATER ON BIA 27.
1.25 3 ENE HILL CITY SD PENNINGTON 0322 PM
1.00 BEULAH WY CROOK 0635 PM
1.00 17 NE RENO JUNCTION WY CAMPBELL 0602 PM
1.00 8 WSW BEULAH WY CROOK 0535 PM
1.00 11 NNE SAVAGETON WY CAMPBELL 0505 PM
1.00 SHARPS CORNER SD OGLALA LAKOTA 0500 PM
1.00 13 NNE SAVAGETON WY CAMPBELL 0446 PM
1.00 10 E DOWNTOWN CUSTER SD CUSTER 0429 PM
1.00 22 WSW DOWNTOWN GILLETT WY CAMPBELL 0420 PM
1.00 2 W HAYWARD SD PENNINGTON 0347 PM
1.00 1 E HILL CITY SD PENNINGTON 0325 PM
GROUND IS WHITE. 0.75 INCHES OF RAIN.
1.00 3 WSW SHERIDAN LAKE SD PENNINGTON 0310 PM
1.00 1 WSW MYSTIC SD PENNINGTON 0220 PM
0.88 3 ESE HILL CITY SD PENNINGTON 0330 PM
NICKEL SIZED HAIL FOR THE LAST 15 MINUTES
0.88 2 ENE HILL CITY SD PENNINGTON 0316 PM
LOTS OF NICKLE AND DIME SIZED HAIL THAT
COVERED THE ROAD. VEHICLES HAD TO PULLOVER.
Tstm wind reports listed by speed (mph)
SPEED LOCATION ST COUNTY TIME
------ ----------------------- -- -------------- -------
70.00 10 W EDGEMONT SD FALL RIVER 0853 PM
70.00 2 WNW FAIRBURN SD CUSTER 0505 PM
70.00 2 NNW FAIRBURN SD CUSTER 0505 PM
65.00 2 SE COLONY WY CROOK 0630 PM
SPOTTER WAS DRIVING FROM BELLE FOURCHE TO
COLONY 12 MILES NW OF BELLE FOURCHE HE
ENCOUNTERED 65 MPH WIND GUSTS AND HEAVY RAIN
65.00 10 WNW DOWNTOWN SPEARFI SD LAWRENCE 0615 PM
65.00 15 N RENO JUNCTION WY CAMPBELL 0529 PM
60.00 3 ENE ROCHELLE WY WESTON 0714 PM
60.00 15 NNW ALVA WY CROOK 0550 PM
60.00 11 NNE SAVAGETON WY CAMPBELL 0505 PM
60.00 15 NNE RECLUSE WY CAMPBELL 0450 PM
60.00 14 NNW SAVAGETON WY CAMPBELL 0425 PM
60.00 22 WSW DOWNTOWN BELLE F WY CROOK 0420 PM
CHAIN LINK FENCE BLOWN DOWN, PATIO FURNITURE
BLOWN ACROSS DECK, DOG HOUSE BLOWN ACROSS
YARD
57.00 3 NW WASTA SD PENNINGTON 0913 PM
57.00 5 SW BEULAH WY CROOK 0626 PM
56.00 3 ESE PINE RIDGE SD OGLALA LAKOTA 1034 PM
56.00 5 NE PORCUPINE SD OGLALA LAKOTA 0620 PM
TIME ESTIMATED FROM RADAR
55.00 8 NW ROCKYPOINT WY CAMPBELL 0540 PM
53.00 RAPID CITY AIRPORT SD PENNINGTON 0844 PM
Rain amounts (inches)
AMOUNT LOCATION ST COUNTY TIME
------ ----------------------- -- -------------- -------
2.70 7 NE SMITHWICK SD FALL RIVER 0700 AM
24-HR RAINFALL.
2.25 6 SW BEULAH WY CROOK 0700 AM
24-HR RAINFALL.
2.05 HILL CITY SD PENNINGTON 0700 AM
24-HR RAINFALL.
1.78 2 ENE EDGEMONT SD FALL RIVER 0700 AM
24-HR RAINFALL.
1.67 14 NW EDGEMONT SD FALL RIVER 0700 AM
24-HR RAINFALL.
1.32 2 SW DOWNTOWN NEWCASTLE WY WESTON 0700 AM
24-HR RAINFALL.
1.25 7 ENE OSAGE WY WESTON 0700 AM
24-HR RAINFALL.
1.25 1 S DOWNTOWN BELLE FOUR SD BUTTE 0700 AM
24-HR RAINFALL.
1.20 2 NW CENTRAL CITY SD LAWRENCE 0700 AM
24-HR RAINFALL.
1.20 HERMOSA SD CUSTER 0700 AM
24-HR RAINFALL.
1.16 6 SSW MYSTIC SD PENNINGTON 0700 AM
24-HR RAINFALL.
1.11 3 SE SAINT ONGE SD LAWRENCE 0700 AM
24-HR RAINFALL.
1.08 3 ESE CHEYENNE CROSSING SD LAWRENCE 0700 AM
24-HR RAINFALL.
1.05 1 WSW DOWNTOWN NEWCASTL WY WESTON 0700 AM
24-HR RAINFALL.
0.99 4 NNE SUMMERSET SD MEADE 0700 AM
24-HR RAINFALL.
0.96 11 NE MORRISEY WY WESTON 0700 AM
24-HR RAINFALL.
0.95 1 N HISEGA SD PENNINGTON 0700 AM
24-HR RAINFALL.
0.90 4 S DOWNTOWN RAPID CITY SD PENNINGTON 0700 AM
24-HR RAINFALL.
0.87 4 NNW DOWNTOWN STURGIS SD MEADE 0700 AM
24-HR RAINFALL.
0.86 6 NNW DOWNTOWN SPEARFIS SD LAWRENCE 0700 AM
24-HR RAINFALL.
0.85 DOWNTOWN HOT SPRINGS SD FALL RIVER 0700 AM
24-HR RAINFALL.
0.84 1 NW DOWNTOWN CUSTER SD CUSTER 0700 AM
24-HR RAINFALL.
0.81 7 SSE SUNDANCE WY CROOK 0700 AM
24-HR RAINFALL.
0.81 TILFORD SD MEADE 0700 AM
24-HR RAINFALL.
0.81 1 SSW DOWNTOWN HOT SPRI SD FALL RIVER 0700 AM
24-HR RAINFALL.
0.77 5 NE ROCKERVILLE SD PENNINGTON 0700 AM
24-HR RAINFALL.
0.75 2 NE BOX ELDER SD PENNINGTON 0700 AM
24-HR RAINFALL.
0.75 1 NE DOWNTOWN RAPID CIT SD PENNINGTON 0700 AM
24-HR RAINFALL.
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