Hail — Adams, Nebraska

2012-05-02 · near Juniata, Adams, Nebraska

Wider weather episode

Multiple severe thunderstorms produced large hail up to softball size, localized flooding rains and one EF1 tornado between the evening of Wednesday the 2nd and early morning hours of Thursday the 3rd. Although no injuries were reported, this was the most significant of several severe weather episodes within South Central Nebraska between May 1st-4th and was also the most prolonged, with dozens of warnings issued over nearly a 12-hour period between 7 PM and 7 AM CDT. Despite the number of storm reports, this event was rather localized as only six counties within the 24-county area bore the brunt of severe weather. Severe storms focused in two primary zones: one a narrow southwest-to-northeast corridor extending from Buffalo through Nance Counties, and the other a concentrated, east-to-west corridor through mainly Adams, Clay and Fillmore Counties. The lone confirmed tornado, which struck after nightfall along the Thayer-Fillmore County line, was only on the ground for approximately one mile but caused considerable damage to a farmstead northeast of Davenport. Several areas experienced hail to at least golf ball size, but some of the most significant hail damage focused in and near northern portions of Hastings, where two separate rounds of large hail occurred between 10 PM-12 AM CDT. During the first round, stones up to softball size were reported within the city, and during the second round 2-inch diameter stones pounded the National Weather Service office. Rainfall wise, the heaviest measured amounts of 3-4 inches targeted much of Clay and Fillmore Counties, resulting in water running over Highway 6 west of Sutton, along with flooding of numerous county roads.

In both primary zones of severe weather described above, things got underway between 7 PM-9 PM CDT. In the northern corridor between Buffalo and Nance Counties, initially linear multicell storms eventually transitioned into brief, semi-discrete supercells, with hail to around golf ball size reported near Amherst, Fullerton and Genoa. By 10 PM CDT, most of this activity north of Interstate 80 had either weakened or moved out of the area to the northeast. Meanwhile, storms within the southern area first developed as a multicell cluster in Nuckolls and Clay Counties. Around sunset, a slow-moving cyclic supercell evolved from this activity, producing the EF1 tornado near Davenport shortly after 10 PM CDT. Although reports of funnel clouds continued as this supercell drifted northeast toward Strang, no additional tornado touchdowns were confirmed. Between 10 PM-2 AM CDT, a nearly solid east-west corridor of hail and heavy rain-producing severe storms trained near the Highway 6 corridor between Adams and Fillmore Counties, as the original tornadic storm exited Fillmore County to the east. Between 2 AM-4 AM CDT, there was a brief lull in storm severity, while additional activity flared up farther north and west near the Interstate 80 and Highway 6 corridors. Finally, between 4 AM-7 AM CDT, one last round of hail-producing severe storms tracked east across parts of Adams, Clay and Fillmore Counties before exiting into eastern Nebraska.

Regarding synoptic and mesoscale forcing, broad southwesterly flow aloft was not overly strong, with South Central Nebraska positioned well south of the primary shortwave trough traversing the Northern Rockies and Northern Plains. As a result, the initiation of severe storms was largely driven by the combination of strong convective instability and low level convergence. At the surface, the northern zone of severe weather was tied to a southwest-to-northeast oriented front/retreating outflow boundary. The initiation of the southern storm cluster and cyclic tornadic supercell appeared to be triggered by persistent moisture convergence along the northeast periphery of a weak surface low in north central Kansas. Once these storms developed, the onset of a modest low level jet after nightfall helped to enhance low level shear profiles, with 0-1 kilometer storm relative helicity around 200 m2/s2 by the time of the EF1 tornado. The mesoscale environment was quite supportive of supercells, with mid-evening parameters including 40 knots of 0-6 kilometer vertical wind shear and at least 3000 J/kg mixed-layer CAPE.

View location on OpenStreetMap → (40.5800, -98.5009)

Source: NOAA Storm Events Database, event_id 376169. Narrative written by the NWS forecast office that issued the report.