Weekend Nor’Easter?

March can be a funny month. Temperatures in the 80s and vicious nor’easters – it’s all possible in March. Our midday computer models today all showed a pretty impressive weekend storm with the Euro and GFS both showing snow – possibly significant snow nearby.

mthk_f168_bg_US

It’s important to note there’s quite a bit of spread in possible solutions. From no storm to warm rainstorm – all options are on the table for Sunday and Monday. The mean solution shown above (basically the average of 51 different European Ensemble members) shows an interesting solution – particularly for the elevated interior of New England.

While a snowstorm is unlikely at this point it’s worth watching this storm.

Pennsylvania Tornadoes

Wednesday’s severe weather outbreak was remarkable given the time of year. 22 tornadoes touched down between Florida and Pennsylvania with 4 of those tornadoes being significant.

The Pennsylvania tornadoes were QLCS tornadoes. The Lancaster County tornado was an EF-2 and on the ground for 5 miles while the one in Bradford County was an EF-1 and on the ground for only a mile. The Lancaster County one was quite impressive on radar and very well warned by the National Weather Service in State College, PA.

lns1

You can see a well defined QLCS with a developing bowing section over southern Lancaster County here at 0017 UTC. The couplet has a rotational velocity of around 24 knots (delta V of 48 knots). Within 11 minutes the couplet becomes substantially stronger. In fact, rotational velocity increases to nearly 60 knots! For a QLCS this is exceptionally powerful and is supportive of a significant tornado.

lns2

By the time tornadogenesis occurs at 0038 UTC the velocity signature is “lost in the haze” so to speak on KDIX (the closest radar site) due to range folding.

lns3

It’s somewhat surprising the tornado didn’t touch down earlier given the strength of the tornado vortex signature that was sampled. However, it’s important to realize that this signature was being sampled nearly 7,000 feet above radar level and the environment was not particularly favorable for tornadoes. Here’s the 1-hour 00z 4km NAM forecast for Lancaster, PA showing anomalously high instability for February (MUCAPE approaching 1,000 j/kg) but a relatively stable boundary layer and certainly not much surface based CAPE.

bufkitprofile

The tornado in northeastern Pennsylvania was much less impressive on radar.

bradford

With only about 20 knots of rotational velocity this tornado signature isn’t going to appear in a textbook anytime soon. What I found most interesting about this storm was how poorly the models were even initializing the nearby environment. Take the 00z 4km NAM for Scranton/Wilkes-Barre (KAVP).

bufkitprofile1

You can see almost no instability (surface based or otherwise) but exceptionally strong shear. Given this model sounding you’d expect the chance for severe weather to be quite low. However, take a look at the 0043 UTC METAR from KAVP.

KAVP 250043Z 16015G27KT 10SM VCTS -RA FEW024 BKN070 OVC110 17/13 A2931 RMK AO2 PK WND 15031/0027 LTG DSNT S-NW P0002 T01670133

The temperature was nearly 6C higher than modeled! What was a model sounding with virtually no instability is really now one with some instability – probably surface based too! This is a good reminder to not get lost in the models during events like this one – observations are important!

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).

Snow, Ice, Rain & Wind

A storm moving in Monday and Tuesday will bring a bit of everything to Connecticut. We’ll start off with some snow for the evening commute on Monday. This initial wave of precipitation is due to warm advection. Basically, the wind is transporting warmer air north dislodging the cold already in place resulting in lift in the atmosphere.

gfsNE_850_temp_036

So, the timing won’t be great and amounts won’t be too great either. This has the look of a relatively minor 1″-3″ kind of deal. What comes after is more of a bummer.

The cold air will be slow to depart and our computer models are notoriously fast in dislodging low level cold. The high resolution NAM does a nice job of showing the cold lingering in the Connecticut River valley through 7 a.m. Tuesday. In fact, while it’s 30F at Bradley Airport its 49F in Willimantic. This is a completely plausible solution!

hires_t2m_boston_43

So, after our snow we’ll be able to add a nice glaze of ice on top of things. Ice will likely linger through the Tuesday morning commute in the Connecticut River Valley near and north of Hartford, the Farmington Valley, as well as the east slopes of the Litchfield Hills. Elsewhere, the torch will have begun.

With a storm tracking to our west temperatures will spike into the 50s in many areas on Tuesday with heavier rain moving in. Gusty winds are possible as well Tuesday as a low level jet develops overhead – some of which will be able to mix down to the ground. 50 mph wind gusts are not out of the question in coastal Connecticut.

Brutal Sunday Morning Cold

KALB.skewt.20160214.00

This is one heck of an Arctic blast. Last night Albany broke their record for coldest 850mb temperature recorded by a weather balloon with an exceptional reading of -31C. Getting those kind of readings over Connecticut is quite unusual!

namNE_850_temp_000

So, how did the numbers shake out?

  • -12F in Hartford is the coldest temperature since February 1996 and is tied for the 24th coldest of all time.
  • -6F in Bridgeport is the coldest temperature since 1984 and tied for the second coldest temperature since records began (only 1948).
  • -1F in Central Park/NYC is the coldest since January 19, 1994 and tied for 41st coldest all-time.
  • -9F in Boston is the coldest temperature since January 15, 1957 and tied for the 20th coldest all-time.