EF0 tornado in Howard County, Nebraska

This tornado briefly touched down approximately 6 miles northeast of Ashton, with a maximum wind speed estimated to be 75 MPH. No damage was reported with this tornado.

There was a lot of active weather across South Central Nebraska on this Wednesday, occurring in multiple episodes throughout the entire day, culminating in seven tornadoes. Three of these tornadoes were classified as EF-1 with the other four producing EF-0 damage. Just after sunrise, scattered showers and thunderstorms developed. While most of these storms were sub-severe, the first severe reports of the day occurred over Franklin county. Just before 10 am CDT, one inch hail fell over parts of Franklin county. These thunderstorms departed into eastern Nebraska by 1 pm CDT. In the wake of the initial storms, several storms, some of which were supercells, formed over Webster and Franklin counties, and congealed into clusters and lifted northeast into Adams and Clay counties. Around 2 pm CDT, hail up to the size of golf balls was reported in and nearby Hastings. As these storm clusters moved north, new isolated supercells formed in surrounding areas, including in their wake. These newly-formed cells were the ones that produced several highly-visible tornadoes over York and Clay counties. Six tornadoes occurred in a two hour period, between 3 and 5 pm CDT, over these counties. Other storms lifted into Nuckolls and Thayer counties from northern Kansas. One of these storms produced 61 mph winds at the Hebron municipal airport just before 5 pm CDT. Just after this time, another isolated supercell formed over Hall county and moved north into Howard county. This storm produced a brief tornado near Ashton and one inch hail near Cotesfield. While this was the last of the severe weather, the thunderstorms were far from over. A squall line, which had been active over southwestern Nebraska, advanced eastward while continuing to weaken. The repeated thunderstorm development resulted in significant rainfall amounts. Measurements of 2 to 3 inches were widespread. The highest total was 3.76 inches, in the town of Harvard and 7 miles southeast of Stromsburg.

These numerous thunderstorms, and the associated severe weather, were a result of lee cyclogenesis over Colorado. A negatively tilted upper-level trough extended from Colorado southeastward to Texas, with the leading edge of a 100 knot upper-level jet streak just to the west. The atmosphere was extremely unstable. Temperatures nearing 80 degrees, with dewpoints approaching 70 degrees, resulted in MLCAPE of 3000 to 3500 J/kg. Deep layer shear was around 40 knots. The supercells that became tornadic occurred in areas where surface winds were significantly veered from the southeast.