During the nighttime hours of June 22nd/23rd, a cluster of severe thunderstorms expanded (QLCS) as it moved from Indiana into Ohio ahead of a seasonably strong shortwave trough shifting through the Great Lakes.
This cluster of storms had previously been responsible for significant/high-end wind gusts across portions of northern Indiana earlier in the night, evolving within and through the heart of a well-predicted SPC Moderate Risk threat area. As the line moved into the National Weather Service (NWS) Wilmington, Ohio (WFO ILN) forecast area, rapid line-embedded mesovortex evolution began in northern Warren County and continued across much of Clinton County, moving very close to both the WFO ILN WSR-88D, and a Ohio Department of Transportation Road Weather Information System (RWIS) site. A 20+ mile EF1 tornado was surveyed beginning near Waynesville, OH, to just south of Wilmington, OH, and included a near-miss of both the WFO and the RWIS site, but allowed for some interesting findings.
Detailed data from the RWIS station was sent to WFO ILN by the ODOT RWIS coordinator, Timothy Boyer, and comes courtesy of ODOT. This data revealed an anomalous mid-summer nocturnal rise in boundary layer theta-e in the hours preceding the QLCS arrival in Warren/Clinton counties.
As background, in our HSLC CSTAR group, Jessica King presented to us the results of her study of numerical simulations of severe weather environments at night in the Ohio Valley/Southeast. The results of her study of severe vs. non-severe events showed that rapid changes in SBCAPE immediately ahead of the line (within the 1-3 hours previous to severe report) was an excellent discriminator vs shear and cooling aloft. Below is a screen capture of her results – notice in the severe-vs.non-severe plots how SBCAPE increases dramatically in the hour(s) previous to severe events. In seemingly most (>90%) of her simulations, SBCAPE increased by 200-600 J/kg within 2 hours of the severe event.
Here is another image from Jessica’s research showing the surface theta-e field ahead of an idealized convective boundary from her study of these severe cases. Notice the narrow plume of significant implied advection in theta-e relative to the convective boundary.
With data from the RWIS, and the timeliness of a 05Z special sounding taken at WFO ILN, augmentation of the 05Z surface conditions to what was in place at 07Z (when the tornado touched down and moved through the area) revealed key thermodynamic changes to the environment occurred in the 2.5 hours between 0430Z sounding launch, and tornadogenesis immediately west of Wilmington. While it’s easy to get caught up with the fact that the RWIS measured an 80 mph gust (image below) as the tornado passed very close by, the surface temperature/dewpoint trends in the hours prior to the tornado are key and critical. There is a steady and impressive rise in surface theta-e as measured by the site. This is in the depth of night (3 AM EDT) — in summer — when rises in surface temperature/dewpoint are very difficult in comparison to strong advection regimes typically seen in the cool season QLCS scenario. The fact this advection occurred in late June is very significant. From a temperature/dewpoint of 71F/69F at sounding release (balloon actually released at 0430Z) to 76/73 at 07Z when a tornado was on the ground very near the RWIS and sounding location, this well-timed and well-located data provided verification to the simulations observed in Jessica’s work. This may seem incidental at first look – only a 5F (temperature) and 4F (dewpoint) rise in 3.5 hours – but for nocturnal QLCSs in mid-summer this equates to a rapid change in near-storm environment and threat.
Using the same SBCAPE/SBCINH computing methods as the 05Z sounding linked via SPC above, augmenting that sounding used the observed surface temperature and dewpoint (subjectively maintaining a similar mixing ratio and temperature lapse rate immediately above the surface), the environment felt by tornadic QLCS near Wilmington featured an SBCAPE rise from 456 (with SBCINH of -269 suggesting elevated storms) to > 2000 J/kg with SBCINH reduction to -25 (suggesting surface based storms). That’s a huge change in threat/environment over the period of 3 hours — at night.
Granted this event was far from a traditional HSLC event which was the crux of Jessica’s study, but as we’ve seen time and time again with nocturnal QLCS events in the Ohio Valley (and elsewhere) amidst strong low level shear, if your boundary layer theta-e advection is aggressive/strong – warning meteorologists should anticipate resultant increase in impacts via damaging wind and/or mesovortex tornadoes provided ambient low level shear/cold pool balance is optimal.
Below is the evolution of the tornadic circulation via KILN WSR-88D (top images) and FAA Terminal Doppler Weather Radar (TDWR) at Dayton, OH (bottom images) which was surveyed to be a 20+ mile EF1. There was even very subtle TDS (reduction in correlation coefficient co-located with the SRM velocity couplet) on KILN from Waynesville to just west of WFO ILN before noise/clutter near the radar masks the signal. For the WSR-88D imagery, upper left quadrant is 0.5 degree reflectivity (with MESO-SAILS 3 invoked), upper right is 0.5 degree SRM. For the TDWR imagery, the bottom left is 0.3 degree reflectivity, and the bottom right is 0.3 degree SRM.
From a wind shear perspective, this event possessed the ingredients seen in other high-impact QLCS nocturnal wind events in the Ohio Valley (and elsewhere), with strong 0-1km effective SRH (owing to a strong west-southwesterly low level jet).
Also of interest, is the SPC Mesoanalysis clearly indicating a large area positive nocturnal surface theta-e advection with relative maximum in advection centered very near WFO ILN in southwest Ohio.