New London County Hailstorm

Hail (and a screw driver) from Mark in Preston

Hail (and a screw driver) from Mark in Preston

When you think of severe weather in Connecticut you probably don’t think about New London County. The southeastern corner of the state is a pit for snow and 99 times out of 100 is where thunderstorms go to die. With the exception of hurricanes – weather weenies in New London County are used to let down after let down after let down.

Today, however, brought a severe storm bonanza to New London County. 3 separate storms brought severe hail to New London County including a report (and picture to go along with it!) of significant hail (hen egg size) in Ledyard.

2" diameter hail in Ledyard

2″ diameter hail in Ledyard from Josh

The severe weather threat today was a bit nebulous but still well forecast. A cold front had bisected the state by midday with a narrow corridor of marginal/moderate instability juxtaposed with fairly strong deep layer shear. Here’s the 18z RAP sounding for Groton around the time of the largest hail reports.

RAP BUFKIT analysis at 17z

RAP BUFKIT analysis at 17z

Dew points over 70F were underneath steep mid level lapse rates – on the order of 7.2 C/KM between 500 and 700mb. Impressive! While MLCAPE values were only around 1000 j/kg a fair amount of that CAPE was located in the hail growth zone (-10 to -30C) and 0-6km shear values were near 40 knots.

It shouldn’t come as a surprise that many of these storms exhibited mid level rotation and the mesocyclones were able to sustain some pretty impressive hail stones. I’ll also throw this out there that the models today were consistently underdone with progged CAPE values today. For example, the 12z OKX sounding had 2500 j/kg of CAPE which was far higher than model forecasts or even 12z model analyses. It’s conceivable that the 1000 j/kg of MLCAPE analyzed at 18z on the RAP may have also been underdone compared to reality.

Handfulls of quarter size hail in Groton

Handfulls of quarter size hail in Groton

The storm that dropped the largest hail pulsed up shortly before 2 p.m. over Montville and the Thames River just a (hail)stone’s throw from Mohegan Sun. The 1754 UTC volume scan from OKX shows an impressive hail core with 65 dbz echoes up to the -20c isotherm (over 20,000 ft AGL) and 72 dbz around 10,000 ft AGL.

1754 volume scan KOKX 88d

1754 volume scan KOKX 88d

While meteorological echoes (part anvil being blown northeast by 70 knot southwesterlies near the Equilibirum level and part other junk) masked the hail spike on the OKX radar but the radar out of Taunton showed an impressive (spatially and vertically) three body scatter spike.

KBOX 88d correlation coeffecient - note blue shading southwest of storm showing hail spike

KBOX 88d correlation coeffecient – note blue shading southwest of storm showing hail spike

Shortly after the storm pulsed over Montville the core of the storm dropped and so did golf ball and hen egg size hail in the far northwest corner of Ledyard near the Thames River and along and west of Avery Hill Road just south of Route 2A. Dual Polarization products showed the hail core descending with a clear signal of hail in Ledyard by 1758 UTC (at 4500 ft AGL).

ledyardhailannotate

1758 UTC KOKX volume scan. Clockwise from top left – 0.5 degree base reflectivity, correlation coefficient, specific differential phase, differential reflectivity

Within an area of high reflectivity (Z between 50 and 60 dbz) you can see a noticeably depressed area of correlation coefficient – in some cases near 0.90. There are also areas of ZDR near zero or even subzero which shows that hail is dominating the signal (hail tumbles as it falls so appears spherical to dual pol radar which leads to a differential reflectivity value near 0).

One thing that’s somewhat interesting is that the southeastern part of the storm has very high KDP values – nearly 4 deg/km while the northwest part of the storm was much lower. While the hail signal was present throughout this region the spike in KDP over the center of Ledyard may indicate a lot of water coated sub-severe hail while the lower KDP over the Thames River and northwest Ledyard in the hail core was where the larger/non-water coated hail was falling. Indeed, this matches up with the reports we received of hail near (or even over) 2″ on the Thames River in far northwest Ledyard with dime to quarter size hail in the center of town.

Golf ball size hail in Ledyard melted to this size about 10 minutes after it fell. Thanks Tom for the picture!

Golf ball size hail in Ledyard melted to this size about 10 minutes after it fell. Thanks Tom for the picture!

I went back and searched through SPC’s storm database and then double checked some of the events in NCDC’s storm data. It appears that the 2″ hail from Ledyard is the largest hail event reported in New London County since 2″ hail was reported in Old Lyme during the 1995 super hailstorm. Incidentally, the largest hail report I can find in New London County was from Groton in May 1969 where baseball size hail was reported. 2.75″ hail (baseball size) only shows up 4 times in the Connecticut SPC storm event database since 1955 and 3 of the 4 were from 1995 and all have been along or east of the Connecticut River.

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5 thoughts on “New London County Hailstorm

  1. Why is it that severe weather tends to die out in Southeastern CT? I always thought that it had something to do with the CT River “cutting the legs out” from underneath the approaching storms. Maybe allowing for some stabilization of the atmosphere in this area. Anytime that Thunderstorms approached from the LI Sound, heading north, they always seemed more severe than those cutting down the state from the northwest. Of course, it is just a guess and was wondering if there is any credence to my little “theory”

    • The main reason is the cool water south of New London County. When winds have any southerly component the cooler Sound will stabilize the atmosphere in southeastern Connecticut. Water temperatures are frequently some of the chilliest between the north fork of Long Island and Fishers Island during the summer than anywhere along the south coast of southern New England. Some storms are able to make it – those include storms with a strong cold pool that are “self-maintaining” and storms that are able to feed off a tremendous amount of instability in the mid levels of the atmosphere.

  2. Living in Ledyard for over 50 years we have seen pea-sized hail only 2 or 3 times before so this was a unique event for sure. Normally we would expect severe weather to propagate down from the north and not arrive from the southwest as this did. Truly amazing hail event.

  3. Nice write up, RH. Regarding the RAP MLCAPE forecast my personal experience at least for ENT and WNE is for it to bee TOO HIGH by about 15-20%

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