Power Pacific system will continue to bring significant impacts for Pacific Northwest into northern California the remainder of the week. Dangerous coastal affects, heavy rain, flooding, strong winds, and higher elevation mountain snow continues. Meanwhile, a storm across the east is set to bring the first accumulating snow to many higher elevations of the Catskills into the central Appalachians. Read More >
Overview
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Severe thunderstorms moved across northeastern Wyoming and western through central South Dakota late Tuesday afternoon (July 16th), continuing past midnight into early Wednesday morning (July 17th). A tornado occurred between Rozet and Moorcroft, Wyoming (south of Interstate-90); flooding was reported in Butte County, South Dakota, washing out some roads; lightning struck near the NWS Doppler radar north of New Underwood, South Dakota, causing a temporary outage; and a brief tornado occurred north-northwest of Vetal in Bennett County, South Dakota. The cloud-to-ground lightning plot to the right shows that most of the area experienced thunderstorms during this event.
Here are a couple links to videos of the Wyoming tornado (video #1 and video #2). |
 24-hour cloud-to-ground lightning from 6 am July 16 to 6 am July 17, 2019 |
Tornadoes:
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Tornado - 3 miles East of Rozet to 6 miles East Rozet
Photo of tornado from Dwayne Sisson  |
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Tornado - 9 miles NNW of Vetal
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The Enhanced Fujita (EF) Scale classifies tornadoes into the following categories:
| EF0 Weak 65-85 mph |
EF1 Moderate 86-110 mph |
EF2 Significant 111-135 mph |
EF3 Severe 136-165 mph |
EF4 Extreme 166-200 mph |
EF5 Catastrophic 200+ mph |
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Flooding & Rainfall
Thunderstorms produced very heavy rainfall and flooding across parts of Butte County, especially in the area south of Hoover through Castle Rock, where some roads were washed out.
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| Radar estimated rainfall from 2:44 to 11:12 pm MDT on July 16th, 2019. Areas in blue are estimates of around 4 inches. |
Photos from Harding County Sheriff's Office
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| South of Hoover on Frog Creek, where road is out | South of Hoover on Frog Creek, where road is out |
Photos from Butte County Sheriff's Office
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| SD HWY 79 at Mile Marker 163.5 | SD HWY 79 at Mile Marker 163.5 | SD HWY 79 at Mile Marker 163.5 | Erk Road in the area of Goeringer Road |
Photos from Markus Erk
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| Erk Road | Erk Road | Erk Road |
Radar
Here is a radar reflectivity loop of the entire severe event for July 16-17, 2019, along with some radar images during the time of the tornadoes in both Wyoming and South Dakota.
| Radar reflectivity animation at 30-min intervals from approximately 3 to 11 pm MDT 16 July 2019 (shortly before the Rapid City radar was disabled by lightning). |
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| Radar image at 7:28 pm MDT 16 July 2019, showing reflectivity (left) and velocity (right). The small yellow cross denotes the approximate location of the tornado at the time it begin between Rozet and Moorcroft (south of Interstate-90). |
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| Radar image at 7:36 pm MDT 16 July 2019, showing reflectivity (left) and velocity (right). The small yellow cross denotes the approximate location of the tornado at the time it ended between Rozet and Moorcroft (south of Interstate-90). The yellow (red) polygon delineates the severe thunderstorm (tornado) warning. |
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| Radar image at 1:23 am MDT 17 July 2019, showing reflectivity (left) and velocity (right). The small yellow cross denotes the approximate location of the tornado 9 miles north-northwest of Vetal, SD. The red polygon delineates the tornado warning. |
Storm Reports
Here are the preliminary severe thunderstorm storm reports for July 16, 2019 (link to reports).
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| Preliminary storm reports for July 16-17, 2019 (green H's represent hail; blue W's represent wind gusts; and red T's represent tornado 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
------ ----------------------- -- -------------- -------
3.00 MOORCROFT WY CROOK 0752 PM
1.75 19 SSW ROZET WY CAMPBELL 0805 PM
1.75 1 S DWTN SPEARFISH SD LAWRENCE 0800 PM
1.50 3 NNE MOORCROFT WY CROOK 0800 PM
1.00 2 S DWTN RAPID CITY SD PENNINGTON 1045 PM
1.00 BEULAH WY CROOK 0805 PM
1.00 9 SSE SUNDANCE WY CROOK 0740 PM
1.00 13 W ROCKYPOINT WY CAMPBELL 0732 PM
1.00 2 NNW SUMMERSET SD MEADE 0336 PM
0.88 15 NNW RECLUSE WY CAMPBELL 0705 PM
0.50 WALL SD PENNINGTON 0120 AM
Tstm wind reports listed by speed (mph)
SPEED LOCATION ST COUNTY TIME
------ ----------------------- -- -------------- -------
81.00 9 ENE BELVIDERE SD JACKSON 0929 PM
70.00 10 W EDGEMONT SD FALL RIVER 0616 PM
65.00 9 SW BATESLAND SD OGLALA LAKOTA 0835 PM
60.00 7 E WANBLEE SD JACKSON 0905 PM
60.00 3 SE DEVILS TOWER WY CROOK 0805 PM
60.00 BEULAH WY CROOK 0805 PM
60.00 4 NW ARGYLE SD CUSTER 0700 PM
RAIN FELL IN 20 MINUTES
58.00 7 E WANBLEE SD JACKSON 0859 PM
52.00 4 SSE WITTEN SD TRIPP 0219 AM
50.00 10 W HARDING SD HARDING 0845 PM
50.00 10 W HARDING SD HARDING 0845 PM
Environment
The atmosphere was very unstable over northeastern Wyoming and western South Dakota on Tuesday, July 16th, 2019, per the information obtained from the weather balloon released in East Rapid City at 6 pm MDT (left image). The vertical wind shear (right image) was rather strong, which favored severe storms with both large hail and damaging winds.
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| July 16, 2019, 6 pm upper-air sounding for Rapid City (00z on the 17th) | July 16, 2019, 6 pm upper-air hodograph for Rapid City (00z on the 17th) |
A moist and unstable air mass was in place with east-to-southeast winds bringing humid air into the region, per the images below. Strong winds well above the ground created more than sufficient vertical wind shear that is needed to sustain severe thunderstorms.
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| SPC surface map valid 7 pm MDT 16 July 2019 | SPC mixed-layer CAPE (a measure of buoyancy) valid 7 pm MDT 16 July 2019 | SPC vertical wind shear from the surface to 6 km above ground (about 18,000 ft) valid 7 pm MDT 16 July 2019 |
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