2023 Kansas Nocturnal Tornado Outbreak

The 2023 Kansas Nocturnal Tornado Outbreak was a rare plains nocturnal tornado event that took place during the overnight hours of June 11, 2023. While nocturnal tornado events are not uncommon in Dixie Alley, one so late in the year over the central plains is extremely unusual. In total, 2 violent tornadoes were confirmed. However, several other strong tornadoes touched down, a few of which were rumored to have reached EF4+ level wind speeds. EF5: 0 EF4: 2 EF3: 6 EF2: 12 EF1: 21 EF0: 22 Total: 63

SPC Outlooks
SPC: On Day 5, SPC highlighted a 15% contour encompassing southwestern Nebraska, northeastern Colorado and extreme northwest Kansas. On Day 4, the risk would be expanded eastward and southward to include much of northern Kansas. However, probabilities were not upgraded beyond 15%. This would hold true for Day 3, only with the inclusion of a significant severe contour. For the initial Day 2 outlook, this was maintained. The 1730z Day 2 update introduced an enhanced risk with a 10% hatched tornado risk. SPC hinted at a “potentially significant severe weather event taking place, with very large hail and a strong, long-track tornado possible.” They also stated that “uncertainties regarding convective evolution over Kansas precludes the introduction of higher severe probabilities.”

With the first Day 1 Outlook, a moderate risk was introduced. At 1300z, the updated outlook included a narrow corridor of heightened severe threat, with a 30% hatched tornado contour and a 45% hatched hail contour. In the words of SPC: “While some uncertainties still exist regarding convective evolution within the warm sector, the kinematic/thermodynamic fields forecast over N KS and resulting volatile parameter space as well as run-to-run consistency of the HRRR displaying several intense discrete supercells within this region will prompt a high risk for this outlook cycle. While somewhat conditional, any sustained surface-based storm within the forecasted environment will have the potential to produce very large to giant hail and significant, long-track tornadoes. Any of these storms that do form are expected to pose a serious threat to life and property.” At 1630z, the hail probabilities would be increased to 60% hatched, the highest possible.

The Atmosphere
One of the biggest problems that precluded the introduction of higher severe probabilities earlier on was a lack of confidence in knowing how surface-based convection would evolve.

Models displayed a potentially volatile environment setting up over KS, with a very deep upper low over Montana digging southeast, then beginning to de-amplify overnight. At first it seemed to be poorly timed for a severe threat, but it ended up being perfectly timed. An 80kt 500mb jet streak would round the base of the trough at around 00z and enter Kansas/Nebraska around 03z. A broad zone of potent moisture advection would bring upper-70s dewpoints northward throughput the day on June 11, in the wake of a surface cold front stalling in central Kansas, then lifting northward in response to cyclogenesis occurring in E Colorado. A high THETA-E air mass was brought northward behind this front, and beneath a stout EML plume. This would result in a rather spectacular thermodynamic field in the WS, with MLCAPE values locally breaching 7500 J/kg. As both vertical speed and directional shear improved dramatically with the arrival of the mid-upper trough and jet streak, the environment was primed for massive hailstones. After 01z, a 60kt LLJ was forecasted. The wind profiles and the thermodynamics (5000 + J/kg MLCAPE) were conducive of strong and even violent long-track tornadoes. A strong capping inversion would hinder convective initiation in Kansas throughout the day. Isolated storms were to form in Colorado during the afternoon and track east into the volatile atmosphere to the east. Around 23-00z, there appeared to be a window for convection to occur around when the cap was at its weakest and the jet kicked in. Rapid supercell development was yo follow, and by 03z a tornado outbreak was expected to take shape (LCLs lowering due to lack of diurnal heating.)

The Tornadoes
The first tornadoes of the day would be produced by some upslope supercells in eastern Wyoming. At 1:35 pm MDT, a single isolated cell fired east of Castle Rock, Colorado, this storm would produce a couple of dusty landspout tornadoes before racing east as the jet arrived. After producing a long swath of large to very large hail, the once high based storm began to steadily move into deeper moisture and become more and more organized. At 6:15 PM CDT, a PDS tornado watch amwas issued for all of northern Kansas and southern Nebraska. The watch gave a 90% chance of one or more strong tornadoes, and also highlighted the threat of widespread very large to giant hail possible. 22z observational data has noted 2 things: a weak confluence line in western Kansas, and a developing THETA-E ridge just northwest of Salina. These features would help initiate storms. A bubbling cumulus field threatened initiation for about an hour, then around 7:06 pm, the first sign of precipitation appeared on reflectivity just west of Selden, KS. Chaser accounts note that the towering cumulus rapidly exploded into a storm, and supercellular characteristics began to appear shortly after initiation. Within 30 minutes it had gained a tornado warning, and at 7:58 pm a funnel cloud was reported north of Dresden. While this storm progressed, the supercell from Colorado entered the more favorable environment over Kansas and got tornado warned once more. It then sequentially produced 2 large EF2 tornadoes, one of which tracked for 23 miles before dissipating. Mobile radar indicated wind speeds in excess of 205 mph, suggesting that it could have produced EF5 level destruction. The storms would persist through the night, producing numerous tornadoes.

The outbreak would result in 12 fatalities (all in Dighton), as well as over 80 injuries. 1 non-tornadic death occurred as a man was impacted by a 5” hailstone near Cawker City, KS. Another interesting feature of this outbreak was a remarkably small number of storms. Only 5 supercells developed in total (in the high risk area), but all of these supercells produced long swaths of destructive hail and tornadoes. The largest hailstone documented was 5.75” and fell about 7 miles southeast of Burlington, Colorado with the longest-lived storm of the event. However, the numerous instances of giant 4+ inch hail as well as swaths of very large hail resulted in significant crop damage. Tornado damage was extensive as well. The event in total cost (including all severe weather related damage): $850 million.

Notable Events
The Stockton-Portis tornado: the first violent tornado of the event. This tornado proceeded a weaker EF1 tornado from a supercell north of Alton. The second tornado was produced by an intense supercell that developed south of Hill City. The tornado began over Rooks County State Park and raced east-northeast, producing high-end EF2 damage on the southeast side of Stockton. The tornado continued through rural land, but produced extreme damage to farmhouses (some of which reportedly had been swept off foundations and vehicles nearby tossed up to half a mile). The tornado proceeded to impact the down of Portis, and caused damage to every structure in town. Shortly after impacting the town the tornado rapidly weakened and then died and occluded. The storm, however, was not done. It would recycle several times and produce 4 more tornadoes, one of which was strong.There are some debates as to whether or not this tornado reached EF5 strength, but most agree it was a high-end EF4.

The more unusual event was the second violent tornado, which was spawned from the last major supercell that developed on the day, forming just outside of Dighton, KS. The supercell would form at approximately 0530z at the intersection of a retreating dryline and an outflow boundary left behind by the decaying supercell from Colorado earlier on. Despite moderate-strong CIN, the strong convergence developed a single supercell. This storm would not even last very long, but it would produce one short-lived and violent tornado that directly impacted Dighton. The tornado tracked only about 6 miles, but produced low-end EF4 damage in the town.