Getting pockets of severe hail is not unusual in Connecticut. Getting a several mile-wide swath of severe, and in some cases significant hail, from the New York border right down to coastal Middlesex County is unusual! The July 1 severe weather event was one of the more prolific hail producers I’ve seen in a few years. In fact the 2″ diameter hail reported in Killingworth and Clinton was the largest hail report in Middlesex County since 1995.
This is where the largest hail fell on July 1st. The red shading is where severe hail (1″ or greater in diameter) fell while the yellow shading is the area that received significant hail (2″ or greater in diameter). In general significant hail is enough to start causing property damage.
The evening 00z OKX sounding showed enough instability to produce severe thunderstorms (CAPE about 2000 j/kg). The 12z OKX sounding was fairly similar. The question was how much would the boundary layer dry out and during the day. As it turned out the boundary layer remained relatively moist yielding more impressive instability than forecast.
The 3 p.m. OKX Vad Wind Profile showed slightly more shear than modeled earlier in the day. More backed winds in the boundary layer not only helped keep the BL moist when combined with a somewhat more veered mid level flow than models had indicated resulted in a favorable shear/instability combination for supercells.
While thunderstorms were expected across the state thanks to a solid 500 mb shortwave rotating around a trough overhead a combination the somewhat more impressive instability and shear than modeled lead to a more impressive severe weather event than I originally anticipated. Almost all of the damage and sig severe reports came from one beast of a supercell that developed near the Catskills and moved into Connecticut. This is what the supercell looked like prior to dropping egg size hail in Watertown. CLASSIC!
You can see here the strong mesocyclone at about 6500ft AGL (also visible at the 1.4º tilt at about 13,000ft AGL) and a V-Notch or what I prefer to call a Flying Eagle. This develops as air is forced around the core of the storm – indicative of a very powerful updraft. In addition three-body scatter spikes or hail spikes are visible from the storms large hail core. Other tilts show the 65 dbz level reaching 27,000ft AGL level. Yup… that’s a big hailer!
The supercell also showed another classic signature on doppler radar with strong storm top divergence (over 100 knots).
This storm relative velocity image at about 35,000 feet AGL shows a strongly divergent flow along a radial near the top of the storm’s updraft. This is why you get a beautiful anvil from a mature cumulonimbus cloud. Generally over 100 knots of storm top divergence means big hail is fairly likely.
The supercell continued southeast right to the Sound, somewhat reminiscent but not as impressive as the June 1995 storm, eventually dropping golf ball and egg size hail in Clinton and Killingworth. Here are two vertical cross sections from the Sound north-northeast into Middlesex County. The y-axis is the vertical with each white line equal to 10,000 feet AGL.
While North Madison only reported hail to the size of quarters Killingworth and Clinton were slammed with significant/2″ diamater hail as the storm’s core collapsed. The suspended hail began to accelerate toward earth as the updraft weakened dropping the largest hail in Middlesex County since the 1995 super-hail supercell which dropped baseballs in Deep River and Essex.
Each severe weather event unique and this was no exception. Our models did not do a particularly good job with either boundary layer moisture, boundary layer veered winds (those 2 really go hand-in-hand) and mid level lapse rates. Using actual soundings, observations, and data like OKX’s Vad Wind Profile was vital in determining the severity of the threat once things developed. Though not particularly well forecast this event was fascinating to watch unfold on Doppler Radar.