Hail — Hall, Nebraska

2014-06-20 · near Grand Is, Hall, Nebraska

Event narrative

Primarily northern and central portions of the city of Grand Island were pounded by hail ranging in size from quarters to baseballs for approximately 30 minutes.

Wider weather episode

Although ground-truth reports of severe-criteria hail and wind emanated from only seven counties mainly within northern and central portions of South Central Nebraska on this Friday, the coverage of non-severe thunderstorms and locally heavy rain became rather widespread across much of the area during the late evening and lasting into the early morning hours of the 21st. Despite the somewhat limited areal coverage of verified severe storms, this was a more-significant-than-expected and fairly long-lasting event, as 25 severe thunderstorm warnings were issued in the local area over the course of eight hours between 230-1030 pm CDT, including for a storm that pounded parts of Grand Island with hail up to baseball size.

Several hours prior to the primary severe weather event, a lone morning storm dropped nickel size hail as it passed through Valley and Greeley counties. During the early stages of the main afternoon/evening development, generally between 230-500 pm CDT, transient clusters of strong to marginally severe multicell storms affected areas north of Highway 92, producing ping pong ball size hail near Cotesfield. The next few hours featured the storms of the day as a pair of very slow-moving supercells pounded the northern Hall and southern Howard county area. For the city of Grand Island, the first of these storms likely resulted in the most significant severe event of the 2014 convective season, as a swath extending from a few miles northwest of the city to near the downtown area was drilled with hail stones ranging from quarter to baseball size between mainly 6-7 pm CDT. During this same time frame, a separate, smaller severe storm in Sherman County dropped very large hail up to 3 in diameter in the Rockville area. As the initial Grand Island supercell started dissipating, a second supercell flared up just to its west over northwestern Hall County mainly between 730-830 pm CDT, pounding the Cairo area with hail up to golf ball size for several minutes. While this second supercell started to weaken, a considerable flare-up of strong to severe multicell convection commenced between 730-900 pm CDT within several northern and western counties such as Sherman, Dawson, Gosper and Furnas, resulting in a few reports of estimated 60-65 MPH winds. Generally between 9-11 pm CDT, much of this widespread convection rapidly congealed into a southeast-surging quasi-linear complex that took aim on the Tri-Cities area. During this time, measured wind gusts in Hall County included 58 MPH at the Grand Island airport and 76 MPH at a home weather station near Wood River. These damaging gusts then barreled into Adams County where Hastings airport measured a 67 MPH gust, resulting in the second round of tree damage and fairly minor structural damage within the city in less than one week's time. Beyond 11 pm CDT, there were no further reports of severe storms within South Central Nebraska, although widespread redevelopment of convection continued through the night, especially near the Interstate 80 and Highway 6 corridors. By the end of the night, most of the 24-county area had tallied anywhere from 0.50 to 2 of rain. However, much higher pockets of at least 3-4 of rain targeted primarily northern Hall and southern Howard counties, northern Adams County and central/western Clay County. A few of the highest storm totals from a combination of automated gauges, NWS cooperative observers and NeRAIN observers included 4.07 five miles west-southwest of Clay Center, 3.31 at Hastings airport and 3.11 three miles east-southeast of Dannebrog. Not surprisingly, short-term flooding issues materialized. While rain was still falling during the evening, water was reported over several county roads in southwestern Howard County, along with Highway 11 near Dannebrog. After daybreak on the 21st, reports arrived of several county roads in northwestern Adams County covered in water.

In the big picture of the mid-upper levels, this was not really a synoptically-evident severe weather setup, thanks largely to the lack of a notable mid-upper level disturbance and also seasonably-weak deep layer wind shear. As a result, the severity/longevity of this event was largely underestimated in official forecasts, even within 12 hours of its onset. In the mid levels, fairly weak quasi-zonal flow containing very subtle disturbances was in place over Nebraska, well to the south of a compact-but-strong closed low churning over Saskatchewan and Manitoba. At the surface, only a few subtle boundaries were present within the region, but no well-defined fronts. However, as afternoon temperatures rose well into the upper 80s-low 90s F in the presence of dewpoints in the mid-upper 60s, significant instability developed in the form of mixed-layer CAPE soaring to between 3000-4000 J/kg. Despite 0-6 kilometer deep layer shear averaging no more than 20-30 knots, this highly unstable environment supported robust convection, including the few slow-moving supercells. After dark, the briefly-severe squall line and subsequent multi-hour period of regenerative non-severe storms was aided by the exit region of a 30-40 knot low level jet centered over western KS.

View location on OpenStreetMap → (40.9200, -98.3500)

Source: NOAA Storm Events Database, event_id 529894. Narrative written by the NWS forecast office that issued the report.