Sunday of Memorial Day weekend featured a prolonged afternoon and evening outbreak of severe thunderstorms primarily within the eastern two-thirds of South Central Nebraska. In addition to dozens of reports of large hail and damaging winds over the course of seven hours between 4-11 PM CDT, there was one brief EF0 tornado reported by storm chasers in a rural area between Greeley and Wolbach around 530 PM CDT with no damage reported. Hail to at least golf ball size fell in several locations, including in or near Greeley, Geneva, Franklin, Riverton, Blue Hill and along Interstate 80 in far eastern York County. In east central Greeley County, at least one home sustained broken windows. Damaging winds estimated from 60 to at least 70 MPH overturned a number of irrigation pivots, destroyed grain bins and downed trees, with some of this wind damage reported in or near Wood River, Blue Hill and Fairfield. Rainfall-wise, several counties received 1-3 inches, with a few of the highest known measured amounts including 2.90 inches southeast of Palmer and 2.88 inches north of Osceola. Although flooding was not widespread, rainfall of around 2.60 inches in the Wood River area resulted in water over a county road.
The primary zone of severe storms was associated with a slow-moving cold front and focused roughly 20 miles either side of the Highway 281 corridor between the Kansas border and the Greeley area. However, a smaller, separate cluster of severe storms also developed east of the frontal zone, affecting counties such as Thayer, Fillmore and eastern York. In both of these areas, the initiation of severe storms occurred between 4-6 PM CDT. During these first few hours, one of the strongest, most discrete supercells of the day produced the brief tornado and large hail in Greeley County before exiting the local area into Boone County. Between 6-8 PM CDT, a mix of brief supercell and quasi-linear multicell storm structures trained along the aforementioned north-south corridor near Highway 281. Then between 8-11 PM CDT, this initially narrow zone of storms expanded eastward as northern storms weakened and southern storms became more dominant. It was during this time frame that a few intense storms passed along a corridor from Franklin to Clay Counties, including a short bowing segment that resulted in several wind damage reports. Finally by 11 PM CDT, storm intensity trended downward and no additional severe weather was reported despite activity lingering well past midnight mainly south of Interstate 80 and east of Highway 281.
This severe weather event was anticipated several days in advance, and featured a Moderate Risk Day 1 Convective Outlook from the Storm Prediction Center. The primary forcing mechanism aloft was a strong shortwave pushing northeast out of Colorado, along the southeast periphery of a deep mid-level low centered in Montana. At the surface, the aforementioned slow-moving cold front served as the primary low-level trigger, as it aligned from northwest Kansas to northeast Nebraska at mid-afternoon. As this strong upper forcing intercepted the cold front and severe storms erupted, mesoscale convective parameters featured between 1000-2000 J/kg mixed-layer CAPE and impressive 0-6 kilometer vertical wind shear of 50-70 knots. A potentially more significant tornado threat was likely kept in check by somewhat high cloud bases, resulting from surface temperature-dewpoint spreads of 20-30F early in the event.

Hail in GREELEY, NEBRASKA
From 27-MAY-12 16:29:00 to 27-MAY-12 16:29:00 (CST-6)
Location: GREELEY
Magnitude: 1.75 
Property damage: 15.00K
Crop damage: 250.00K
Reported by: COOP Observer

Hail in GREELEY, NEBRASKA
From 27-MAY-12 16:30:00 to 27-MAY-12 16:30:00 (CST-6)
Location: GREELEY
Magnitude: 1.75 
Property damage: 15.00K
Crop damage: 250.00K
Reported by: COOP Observer

Hail in FRANKLIN, NEBRASKA
From 27-MAY-12 17:38:00 to 27-MAY-12 17:42:00 (CST-6)
Location: RIVERTON
Magnitude: 2.00 
Property damage: 50.00K
Crop damage: 1.50M
Reported by: Storm Chaser

Thunderstorm Wind in WEBSTER, NEBRASKA
From 27-MAY-12 20:13:00 to 27-MAY-12 20:13:00 (CST-6)
Location: BLADEN
Magnitude: 52.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Tree branches of 3 inches in diameter were blown down.

Hail in WEBSTER, NEBRASKA
From 27-MAY-12 20:15:00 to 27-MAY-12 20:15:00 (CST-6)
Location: BLADEN
Magnitude: 1.50 
Property damage: 25.00K
Crop damage: 500.00K
Reported by: Public

Hail in FRANKLIN, NEBRASKA
From 27-MAY-12 20:45:00 to 27-MAY-12 20:45:00 (CST-6)
Location: CAMPBELL
Magnitude: 1.50 
Property damage: 25.00K
Crop damage: 1.00M
Reported by: Law Enforcement

Hail in GREELEY, NEBRASKA
From 27-MAY-12 15:33:00 to 27-MAY-12 15:33:00 (CST-6)
Location: SPALDING
Magnitude: 1.75 
Property damage: 25.00K
Crop damage: 250.00K
Reported by: Trained Spotter

Tornado in GREELEY, NEBRASKA
From 27-MAY-12 16:23:00 to 27-MAY-12 16:24:00 (CST-6)
Location: GREELEY
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Storm Chaser

No damage was reported with this brief tornado touchdown.

Thunderstorm Wind in GREELEY, NEBRASKA
From 27-MAY-12 16:30:00 to 27-MAY-12 16:30:00 (CST-6)
Location: GREELEY
Magnitude: 52.00 EG
Property damage: 25.00K
Crop damage: 250.00K
Reported by: Public

Small tree branches were blown down at a home and hail of unknown size resulted in broken house windows and a broken windshield.

Hail in THAYER, NEBRASKA
From 27-MAY-12 16:39:00 to 27-MAY-12 16:39:00 (CST-6)
Location: BRUNING
Magnitude: 1.25 
Property damage: 15.00K
Crop damage: 150.00K
Reported by: Storm Chaser

Hail in FILLMORE, NEBRASKA
From 27-MAY-12 17:15:00 to 27-MAY-12 17:15:00 (CST-6)
Location: GENEVA
Magnitude: 1.75 
Property damage: 75.00K
Crop damage: 500.00K
Reported by: Emergency Manager

Hail in YORK, NEBRASKA
From 27-MAY-12 17:18:00 to 27-MAY-12 17:18:00 (CST-6)
Location: WACO
Magnitude: 1.75 
Property damage: 75.00K
Crop damage: 500.00K
Reported by: Trained Spotter

Hail in FRANKLIN, NEBRASKA
From 27-MAY-12 17:25:00 to 27-MAY-12 17:30:00 (CST-6)
Location: RIVERTON
Magnitude: 1.50 
Property damage: 25.00K
Crop damage: 400.00K
Reported by: COOP Observer

Hail in WEBSTER, NEBRASKA
From 27-MAY-12 17:37:00 to 27-MAY-12 17:37:00 (CST-6)
Location: INAVALE
Magnitude: 1.50 
Property damage: 25.00K
Crop damage: 400.00K
Reported by: Law Enforcement

Hail in FRANKLIN, NEBRASKA
From 27-MAY-12 17:55:00 to 27-MAY-12 17:55:00 (CST-6)
Location: FRANKLIN
Magnitude: 2.00 
Property damage: 75.00K
Crop damage: 1.00M
Reported by: Storm Chaser

Thunderstorm Wind in HALL, NEBRASKA
From 27-MAY-12 18:00:00 to 27-MAY-12 18:10:00 (CST-6)
Location: WOOD RIVER
Magnitude: 61.00 EG
Property damage: 350.00K
Crop damage: 250.00K
Reported by: Fire Department/Rescue

Numerous irrigation pivots were overturned along an approximately 6 mile long path from Wood River south to near Interstate 80.  In Wood River, large trees were damaged or destroyed and power poles were knocked down.  Heavy rain from these thunderstorms resulted in the intersection of 140th and Holling Roads, just south of town, being covered in water.

Hail in WEBSTER, NEBRASKA
From 27-MAY-12 19:49:00 to 27-MAY-12 19:49:00 (CST-6)
Location: BLADEN
Magnitude: 1.00 
Property damage: 45.00K
Crop damage: 500.00K
Reported by: Public

Damage to area crops, roofs and siding was reported.

Thunderstorm Wind in ADAMS, NEBRASKA
From 27-MAY-12 20:25:00 to 27-MAY-12 20:25:00 (CST-6)
Location: AYR
Magnitude: 61.00 EG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Wind gusts were estimated between 60 and 70 mph.

Hail in POLK, NEBRASKA
From 27-MAY-12 20:20:00 to 27-MAY-12 20:20:00 (CST-6)
Location: OSCEOLA
Magnitude: 1.50 
Property damage: 50.00K
Crop damage: 500.00K
Reported by: Trained Spotter

Hail in WEBSTER, NEBRASKA
From 27-MAY-12 20:30:00 to 27-MAY-12 20:30:00 (CST-6)
Location: BLUE HILL
Magnitude: 1.75 
Property damage: 25.00K
Crop damage: 500.00K
Reported by: COOP Observer

Thunderstorm Wind in FRANKLIN, NEBRASKA
From 27-MAY-12 20:45:00 to 27-MAY-12 20:45:00 (CST-6)
Location: UPLAND
Magnitude: 61.00 EG
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Wind gusts estimated at 70 mph resulted in a grain bin being destroyed.

Thunderstorm Wind in CLAY, NEBRASKA
From 27-MAY-12 20:46:00 to 27-MAY-12 20:46:00 (CST-6)
Location: FAIRFIELD
Magnitude: 61.00 EG
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Public

Wind gusts estimated at 70 mph resulted in 2 irrigation pivots being overturned.

Hail in GREELEY, NEBRASKA
From 27-MAY-12 15:13:00 to 27-MAY-12 15:13:00 (CST-6)
Location: GREELEY
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Hail in GREELEY, NEBRASKA
From 27-MAY-12 15:27:00 to 27-MAY-12 15:27:00 (CST-6)
Location: SPALDING
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Hail in SHERMAN, NEBRASKA
From 27-MAY-12 15:49:00 to 27-MAY-12 15:49:00 (CST-6)
Location: ASHTON
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in SHERMAN, NEBRASKA
From 27-MAY-12 16:05:00 to 27-MAY-12 16:05:00 (CST-6)
Location: LOUP CITY
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Employee

Hail in THAYER, NEBRASKA
From 27-MAY-12 16:15:00 to 27-MAY-12 16:27:00 (CST-6)
Location: HEBRON
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Hail in BUFFALO, NEBRASKA
From 27-MAY-12 16:19:00 to 27-MAY-12 16:19:00 (CST-6)
Location: RAVENNA
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Storm Chaser

Hail in THAYER, NEBRASKA
From 27-MAY-12 16:20:00 to 27-MAY-12 16:20:00 (CST-6)
Location: HEBRON
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in THAYER, NEBRASKA
From 27-MAY-12 16:15:00 to 27-MAY-12 16:25:00 (CST-6)
Location: HEBRON
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Hail in SHERMAN, NEBRASKA
From 27-MAY-12 16:25:00 to 27-MAY-12 16:25:00 (CST-6)
Location: ASHTON
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Employee

Hail in FILLMORE, NEBRASKA
From 27-MAY-12 16:46:00 to 27-MAY-12 16:46:00 (CST-6)
Location: OHIOWA
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in FILLMORE, NEBRASKA
From 27-MAY-12 16:57:00 to 27-MAY-12 16:57:00 (CST-6)
Location: MILLIGAN
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Hail in THAYER, NEBRASKA
From 27-MAY-12 17:00:00 to 27-MAY-12 17:00:00 (CST-6)
Location: CARLETON
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in HALL, NEBRASKA
From 27-MAY-12 17:06:00 to 27-MAY-12 17:06:00 (CST-6)
Location: WOOD RIVER
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Storm Chaser

Hail in FILLMORE, NEBRASKA
From 27-MAY-12 17:00:00 to 27-MAY-12 17:15:00 (CST-6)
Location: GENEVA
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in BUFFALO, NEBRASKA
From 27-MAY-12 17:33:00 to 27-MAY-12 17:33:00 (CST-6)
Location: GIBBON
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in HOWARD, NEBRASKA
From 27-MAY-12 17:42:00 to 27-MAY-12 17:42:00 (CST-6)
Location: FARWELL
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Employee

Hail in FRANKLIN, NEBRASKA
From 27-MAY-12 18:12:00 to 27-MAY-12 18:12:00 (CST-6)
Location: BLOOMINGTON
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Storm Chaser

Hail in HALL, NEBRASKA
From 27-MAY-12 18:25:00 to 27-MAY-12 18:25:00 (CST-6)
Location: GRAND IS
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Storm Chaser

Thunderstorm Wind in POLK, NEBRASKA
From 27-MAY-12 20:15:00 to 27-MAY-12 20:15:00 (CST-6)
Location: OSCEOLA
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Wind gusts were estimated at 60 mph.

Hail in ADAMS, NEBRASKA
From 27-MAY-12 20:35:00 to 27-MAY-12 20:35:00 (CST-6)
Location: HASTINGS
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Hail in THAYER, NEBRASKA
From 27-MAY-12 21:17:00 to 27-MAY-12 21:17:00 (CST-6)
Location: CARLETON
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Hail in ADAMS, NEBRASKA
From 27-MAY-12 21:43:00 to 27-MAY-12 21:43:00 (CST-6)
Location: HASTINGS
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Hail in ADAMS, NEBRASKA
From 27-MAY-12 20:25:00 to 27-MAY-12 20:25:00 (CST-6)
Location: AYR
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter