Severe hail and winds occurred in a few spots, along with a brief tornado on this Memorial Day (Monday) evening. However, the biggest story was repeated waves of heavy rain from the 26th that resulted in extensive flooding, and more heavy rain was to come. During the evening, several thunderstorms developed over north central Kansas. All but one of these storms moved northeast into south central Nebraska and affected areas mainly along and east of Highway 281 between 830 and 1130 PM CST. These storms generally remained sub-severe, but a brief EF-0 tornado occurred in Superior at 945 PM CST. The storms had congealed and become quasi-linear, but the low-level and deep-layer shear and SRH were very high, resulting in a shear-dominant line with the most intense cores at the back edge of the line. Along the updraft-downdraft convergence zone, a very small, brief mesovortex formed and produced the tornado. This occurred within a developing bookend vortex, just north of the rear-inflow notch. The one storm that moved different from all the others was a left-moving supercell that originated from a cell split over Rooks county Kansas. That storm moved due north from Alma to Kearney to Loup City from 8 to 945 PM CST, producing quarter size hail in Wilcox and 1 to 2 inch hail in Kearney. Meanwhile, scattered thunderstorms were on-going over southwest Nebraska. These storms entered western Dawson county around 10 PM CST, and during the following two hours these storms organized into a squall line that extended from Ord to Loup City to Lexington to near McCook by 12 AM CST. These storms produced golf ball size hail in and east of Gothenburg, and measured winds of 58 MPH at Cozad. Quarter size hail also occurred in Miller and Ravenna. This line broken into two separate lines, one of which moved east between Interstate 80 and Highway 6, and the other north of the Interstate. The storms remained sub-severe, but a wind gust of 55 MPH was measured at the Hastings airport, and nickel size hail occurred in York. A third cluster of scattered storms developed over southwest Nebraska around midnight. These storms consolidated into a multicell cluster and moved from west to east across the region from 2 to 530 AM CST Tuesday the 28th. These storms were not severe, but they added to the rainfall totals. Total rainfall amounts from all three thunderstorm episodes were not excessive, but given that 2 to 4 inches fell across a large portion of south central Nebraska just 24 hours before, an additional 1 to 2 inches was not needed.
Water levels were already rising on area creeks and rivers from the heavy rain Sunday night. Flooding began to occur as an increasing number of creeks and rivers overflowed their banks through the day. Minor flooding began around sunrise Monday on the upper portions of the Little Blue River from southeastern Adams county into northern Nuckolls county. The Republican River at Riverton had also risen above flood stage. Thompson Creek, which also passes through Riverton, rapidly increased to moderate flood stage. Whatever impacts might have occurred were not known. In Polk county, extensive flooding resulted in numerous road closures. Bridges on gravel roads had water flowing over them. Highway 81 between Osceola and Shelby was closed because it was impassable. The emergency manager stated that the flooding was worse than what occurred in March of this year. Throughout the day, extensive flooding developed over more and more low-lying areas, creeks, and rivers in south central Nebraska. Numerous mostly gravel roads were impassable. All of the counties along and south of the Platte River were affected, although the Platte River itself did not flood. As flooding worsened along the Little Blue River, the Crystal Lake State Recreation Area near Ayr had to be evacuated and closed. Highway 5 north of Deshler was closed due to the Little Blue River. U.S. Highway 6 near Sutton was closed due to floodwater covering the road. The Republican River also went into flood from Guide Rock to Hardy. Across Hamilton, York, and Polk counties, the West Fork of the Big Blue River, the Big Blue River, Lincoln Creek, and Beaver Creek all flooded. In Merrick county, extensive flooding occurred due to Prairie and Silver Creeks. In Dawson and Buffalo counties, Buffalo and Spring Creeks flooded, as well as Mud Creek near Ravenna. Prairie Dog Creek also flooded southwest of Harlan County Lake. This was the second significant flood to occur since the record and near-record flooding in March 2019.
A quasi-stationary front extended from the Mid-Atlantic across the Midwest to low pressure over Iowa. The front then extended southwest across Nebraska and Kansas to another low over Colorado. In the upper-levels, a longwave trough was over the western U.S., with a fairly flat ridge over the east. An upper low moved from Nevada into Utah through the day with southwest flow over the Central Plains. Just before the storms moved into south central Nebraska, temperatures were in the 70s, with dewpoints in the 60s. Despite low mid-level lapse rates, MUCAPE was between 2000 and 3000 J/kg. Deep layer shear was very strong (60-70 kt), with 0-3 km SRH 250-500 m2/s2, with the highest values on the cool side of the front, where low-level winds were most-backed. The persistence of the atmosphere to initiate multiple thunderstorm episodes was impressive, but even more impressive was that they each moved downstream over the same area, between the surface and 850 mb fronts. The initial storms clearly did not exhaust the instability. Through the night, the low over Colorado moved into western Kansas. This maintained the low-level jet, which terminated at the 850 mb front. The low-level jet did not move. The 850 mb front remained stalled near the Kansas-Nebraska border, along with the terminus of maximum 850 mb moisture transport and the 850 mb theta-e ridge.

Thunderstorm Wind in DAWSON, NEBRASKA
From 27-MAY-19 22:30:00 to 27-MAY-19 22:30:00 (CST-6)
Location: COZAD
Magnitude: 50.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

A 58 MPH wind gust was measured by a mesonet site located 1 mile north-northeast of Cozad.

Hail in BUFFALO, NEBRASKA
From 27-MAY-19 23:12:00 to 27-MAY-19 23:12:00 (CST-6)
Location: MILLER
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Hail in BUFFALO, NEBRASKA
From 27-MAY-19 20:59:00 to 27-MAY-19 21:09:00 (CST-6)
Location: KEARNEY
Magnitude: 2.00 
Property damage: 1.00M
Crop damage: 0.00K
Reported by: NWS Employee

Hail ranging in size from 1 to 2 inches in diameter was reported across Kearney.

Tornado in NUCKOLLS, NEBRASKA
From 27-MAY-19 21:45:00 to 27-MAY-19 21:46:00 (CST-6)
Location: SUPERIOR
Tornado F-scale: EF0
Property damage: 75.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

A brief tornado touched down in the center of Superior and severely damaged a detached garage. Shingle and gutter damage was also noted at the adjacent house. Fence and tree damage was common in the neighborhood. This tornado had an estimated maximum wind speed of 81 MPH.

Hail in DAWSON, NEBRASKA
From 27-MAY-19 21:59:00 to 27-MAY-19 22:01:00 (CST-6)
Location: GOTHENBURG
Magnitude: 1.75 
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in DAWSON, NEBRASKA
From 27-MAY-19 22:20:00 to 27-MAY-19 22:20:00 (CST-6)
Location: WILLOW IS
Magnitude: 1.75 
Property damage: 25.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Hail in KEARNEY, NEBRASKA
From 27-MAY-19 20:29:00 to 27-MAY-19 20:29:00 (CST-6)
Location: WILCOX
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in BUFFALO, NEBRASKA
From 27-MAY-19 23:58:00 to 27-MAY-19 23:58:00 (CST-6)
Location: RAVENNA
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Hail in YORK, NEBRASKA
From 28-MAY-19 02:30:00 to 28-MAY-19 02:30:00 (CST-6)
Location: YORK
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media