Severe thunderstorms produced very large hail and damaging winds across portions of Osborne, Jewell, and Mitchell counties late on this Saturday afternoon. Between 2 and 3 PM CST, the first couple storms began forming south and southwest of Hill City. Around 330 PM CST, one storm moved into southwestern Rooks county. It was joined by several other storms which continued to develop along I-70 between Wakeeney and Russell. As the Rooks county storm moved east, these storms moved north and they all merged over Osborne county. Just prior to the merger, a left-moving supercell, fresh after the split, produced hail up to the size of tennis balls near the southern border of Osborne county. After the merger, the newly-formed multicell cluster took the form of a small bow echo as it moved across Mitchell county between 5 and 6 PM CST. The mesoscale convective system produced strong downburst winds that were estimated at 60 mph over central Osborne county and measured at 66 mph over Mitchell county, just west of Beloit. While this was occurring, other cells formed over Jewell county and became severe. Before merging, the southern storm produced a measured wind gust of 78 mph in the town of Jewell, while the northern one produced spotty wind damage from the town of Mankato to Lovewell Reservoir. Tree limbs were snapped off in Mankato, at least one power pole was snapped off northeast of town, and an old county communications building suffered damage as the powerful downburst winds blew the roof off. Rain then damaged the radio equipment housed inside.
These storms formed along and ahead of a Canadian cold front. The flow aloft was west-southwest from Arizona to Maine and it was low in amplitude. A shortwave trough was along the New Mexico-Texas border and lifting northeast. Before the thunderstorms moved in, temperatures were near 90 with dewpoints in the middle to upper 60s. Mid-level lapse rates were near 7.0 C/km. This resulted in MLCAPE around 2000 J/kg. Deep layer shear was around 40 kt.
This event was one of several episodes of heavy convective rains that contributed to a very wet start to September. This event alone produced 3 to 4 inch rain amounts over parts of Osborne and Mitchell counties as scattered non-severe storms continued to develop through the night, after the severe storms had exited north central Kansas. Four-day rainfall totals ending on the morning of the 5th ranged from 3 to 6 inches over Osborne, Mitchell, and Jewell counties. The highest rainfall amounts included 6.55 at Cawker City, 5.98 at Jewell, 5.22 at Beloit, and 5.20 at Osborne.

Hail in MITCHELL, KANSAS
From 01-SEP-18 17:18:00 to 01-SEP-18 17:18:00 (CST-6)
Location: CAWKER CITY
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in OSBORNE, KANSAS
From 01-SEP-18 17:08:00 to 01-SEP-18 17:08:00 (CST-6)
Location: OSBORNE
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Wind gusts were estimated to be near 60 MPH.

Thunderstorm Wind in MITCHELL, KANSAS
From 01-SEP-18 17:35:00 to 01-SEP-18 17:35:00 (CST-6)
Location: BELOIT
Magnitude: 57.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Heavy Rain in MITCHELL, KANSAS
From 01-SEP-18 06:00:00 to 02-SEP-18 06:00:00 (CST-6)
Location: CAWKER CITY
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

A 24 hour rainfall total of 4.10 inches was reported, with the brunt of the rain falling between 5 PM CDT on the 1st and 4 AM CDT on the 2nd.

Heavy Rain in OSBORNE, KANSAS
From 01-SEP-18 06:00:00 to 02-SEP-18 06:00:00 (CST-6)
Location: OSBORNE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

A 24 hour rainfall total of 3.41 inches was reported, with the brunt of the rain falling between 5 PM CDT on the 1st and 4 AM CDT on the 2nd. A total of 3.30 inches was also reported near Covert.

Hail in OSBORNE, KANSAS
From 01-SEP-18 17:08:00 to 01-SEP-18 17:11:00 (CST-6)
Location: COVERT
Magnitude: 2.50 
Property damage: 250.00K
Crop damage: 500.00K
Reported by: Trained Spotter

Hail ranging in size from quarters to tennis balls was reported.

Thunderstorm Wind in JEWELL, KANSAS
From 01-SEP-18 17:13:00 to 01-SEP-18 17:20:00 (CST-6)
Location: MANKATO
Magnitude: 61.00 EG
Property damage: 50.00K
Crop damage: 1.00M
Reported by: Emergency Manager

Wind gusts estimated to be near 70 MPH resulted in tree limbs being downed in Mankato and a power pole being snapped near Montrose. In the Lovewell State Park area, a roof of an old radio communications building was torn off and nearby crops were damaged.

Thunderstorm Wind in JEWELL, KANSAS
From 01-SEP-18 17:19:00 to 01-SEP-18 17:19:00 (CST-6)
Location: JEWELL
Magnitude: 68.00 MG
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Mesonet