Rare February Severe Thunderstorms

stamford

Getting an isolated severe thunderstorm in the winter is unusual. Getting a legitimate severe weather outbreak in February is basically unheard of around here. According to the Storm Prediction Center last night’s severe thunderstorm watch in Connecticut was the first on record (since 1970). At the height of the storm 89,000 utility customers were without power and a wind gust to 68 mph was recorded at Brainard Field in Hartford.

KHFD 250603Z AUTO 18038G59KT 1 1/4SM +TSRA BR SQ BKN016 OVC026 17/16 A2935 RMK AO2 PK WND 16059/0602 LTG DSNT ALQDS PRESRR P0015 T01720156

Even before the storms damaging winds were reaching the surface. At 9:59 p.m. a warning-criteria 50 knot of 58 mph wind was recorded in Bridgeport.

KBDR 250452Z 17028G41KT 8SM BKN015 BKN020 OVC028 16/14 A2935 RMK AO2 PK WND 16050/0359 LTG DSNT SW-NW RAE0357B10E19 SLP939 P0000 T01560139 401560022

So what lead to the storms? The evening weather balloon launch on Long Island shows a relatively impressive amount of elevated instability for the time of year.

OKX

While there is an inversion near the surface (mainly due to the marine influence – remember the Sound and the Atlantic are in the 40s!!) this is an impressive sounding. A proximity sounding for Hartford from the 6z HRRR initialization shows an even more impressive sounding.

HFDHRRR

Elevated CAPE of 768 j/kg (from a parcel lifted at 847mb) with a shallow mixed layer near the surface is a big red flag that we were in trouble. This sounding would be supportive of 50 mph gusts without thunderstorms. Throw in convection and we’re talking about the ability to mix down more momentum from aloft. There’s your 59 knot gust in Hartford!

Indeed, as the thunderstorms were rolling through the Hartford area at 1 a.m. the velocity data was impressive. At approximately 4,000 feet above the ground the radar out of Long Island was sampling winds over over 100 knots!

hfd

Interestingly, the 59 knot gust in Hartford occurred about 10 minutes after the highest reflectivity (which was coincident with the highest outbound velocities) moved through. I’m not quite sure why that would be the case. In fact at 0602 UTC there was only light rain over KHFD per radar with the heaviest echoes well north and east.

Last night’s event was truly unique. A tornado outbreak in the Mid Atlantic with a widespread severe weather event in southern New England during the overnight hours in February! The models did a nice job ramping up the potential for severe weather as the cold, stable wedge eroded and the boundary layer became less and less inverted. At my house in West Hartford my heavily tree covered anemometer recorded a (record) peak gust of 43 mph after we mixed.

My Personal Weather Station
My Personal Weather Station in West Hartford

The 59 knot gust in Hartford was the strongest wind gust we could find at the ASOS station back to 1998 – though that does not include Hurricane Sandy because the power was knocked out.

Kudos to the Storm Prediction Center for the good lead time on the severe thunderstorm watches and our computer models showing the potential. Additionally, this is another great testament to how useful the HRRR can be in these situations. The presence of solid CAPE (850mb dew points in the mid 50s and 500-700mb lapse rates of 6.5C/km!) with an increasingly less inverted boundary layer was a big red flag the potential for destructive winds was rapidly increasing through the evening (you can see signs of this starting on the 00 UTC HRRR run).

6 thoughts on “Rare February Severe Thunderstorms”

  1. Great Stuff! With regard to the delay in warning criteria winds, post highest Dbz, they were experiencing the same lag in some of the NC storms. I was following the discussion on NWSChat, with the NWS requesting media partners to emphasize the lag to the public. I forget the reason for the lag, the chat room log only goes back so far 🙁

  2. “Interestingly, the 59 knot gust in Hartford occurred about 10 minutes after the highest reflectivity (which was coincident with the highest outbound velocities) moved through. I’m not quite sure why that would be the case. In fact at 0602 UTC there was only light rain over KHFD per radar with the heaviest echoes well north and east.”

    I think the storms were moving so quickly there was a lag with the precip, at least. Not sure if that’d be the same case with the wind.

  3. 47 mph gust in North Haven (12:07am)… Gusts up to 45 through 1:30am… Small limbs down every and a few large trees. The winds were consistently higher-sustained than Irene and Sandy here. We were right on the edge of a cell where the front line winds were strong.

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