What’s a Nor’Easter?

The weather geek echo chamber erupted this afternoon following a Weather Channel headline and subsequent Capital Weather Gang article about the headline “Nor’easter to Threaten Millions”

While the “threat” is a fairly minor one – a few inches of rain could lead to some isolated flooding up in Maine as well as gusty winds along the coast north of Boston. This lead me to wonder – what storms deserve the moniker “nor’easter” and what storms don’t.

The answer to this is complex, subjective, and varies from location to location. Here’s the broad definition from the American Meteorological Society Glossary.

noreaster

The key phrases here are “within 100 miles east or west of the coastline” and “winds of gale force”. In order to qualify as a nor’easter locally I save the distinction for storms that produce gale force winds or greater on Long Island Sound that are from the northeast.

The bottom line is that while this storm may be considered a nor’easter for our friends in Maine it’s not a nor’easter down here in Connecticut. It’s just some rain.

As for the headline from The Weather Channel – I get the frustration some have with the somewhat dramatic and ominous description. It’s a fine line but at the end of the day The Weather Channel’s website is a business. It’s a highly successful business and the way that business thrives is on advertising revenue through clicks and page views from a global audience. I’m guessing my suggested headline of “FAIRLY WEAK STORM TO BRING BENEFICIAL RAIN TO NEW ENGLAND” wouldn’t draw too many eyeballs to weather.com!

Incredible Microburst Levels Forest On Part of Mount Tom

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An incredible microburst this morning in Easthampton and Holyoke, Massachusetts leveled a sizable part of a forest on the west side of Mount Tom. A drone that flew over the damage caught this incredible site with thousands upon thousands of trees snapped in half by the powerful winds.

The environment was conducive to severe thunderstorms and while damage was isolated in Connecticut this microburst across the border was very very impressive.

Here’s how the storm looked on radar prior to the downburst. It was only marginally impressive with some exceptionally weak/broad rotation at 8:37 UTC.

broadmesoBy 8:46 UTC the cell appears to be “bowing out” a bit on reflectivity taking on the shape of a backwards “C” while outbound velocities at ~6kft AGL strengthen a bit more. Also, Barnes ANG Base records a wind gust to 48 knots.

KBAF 080846Z AUTO 18032G48KT 130V220 3SM +RA BR SQ SCT013 BKN023 OVC034 17/16 A2971 RMK AO2 PK WND 18048/0846 RAE0759B15 P0007 T01720156

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2 minutes later radar shows a more well defined inflow notch as the reflectivity echoes over the microburst race northeast.

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This was the result.

Bzb4yBSCYAA73gC Bzb8CpjCEAAlRBz BzcDT03CcAAadprAs you can see in the bottom image a huge portion of forest on the west side of Mount Tom was destroyed by a vicious wind storm.

Initially I thought the volume scan at 8:48 UTC was depicting a divergent wind signature which is typical of microbursts. Upon further thought I don’t think that was the case. The radar was sampling the atmosphere at over 6,000 ft AGL which is far too high to capture a divergent wind signature from a microburst hitting the ground. More likely, the radar showed a rapid evolution from a fairly ordinary cell to a quick hitting bow echo with a rear inflow jet aided by a low level jet in excess of 60 knots. The “inbound” velocities that you see in the radar image above were likely from a poorly sampled comma head or bookend vortex that quickly formed as the rear inflow jet developed.

Winds were up to 100 mph from this microburst that was approximately 1/4 mile wide and about 1 mile long from the Easthampton/Holyoke town line and points north along the west slope of Mount Tom.

Based on the aerial pictures from earlier today here’s an approximate representation of the damage path.

Microburst1

Overnight Trouble?

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A nocturnal severe weather event is pretty unusual in southern New England but not unheard of. Tonight we have a set of ingredients that appears favorable for some severe weather from New Jersey up through eastern Massachusetts.

A powerful shortwave trough will race toward southern New England while a powerful low level jet develops overhead in response to strengthening synoptic scale/QG forcing.

namNE_500_avort_012

 

The question is how much instability will there be? We know that the atmosphere will be highly sheared (0-1km shear values in excess of 40 knots) but without the necessary instability the severe weather risk is low.

Our models have shown several different possibilities with the NAM and SREF remaining on the unstable side of things while the GFS has remained more modest.

SREF 3hr MLCAPE. Courtesy: Greg Carbin/SPC

SREF 3hr MLCAPE at KIJD | Courtesy: Greg Carbin/SPC

If moisture is able to stream north and moisten the boundary layer sufficiently, and lapse rates just above the boundary layer remain steep enough, enough CAPE will be present for severe thunderstorms and tornadoes tonight. The shear is even sufficient for a significant tornado in southern New England IF (and it’s a big IF) enough CAPE can be found. Damaging winds will also be possible with such strong winds just off the deck.

Stay weather aware late tonight- it could be an interesting morning!

Another New York Tornado Debris Signature

An EF-1 tornado in North Chemung, NY touched down last week on September 2. According to a Public Information Statement from the National Weather Service in Binghamton, NY the tornado was on the ground for 6 miles and felled numerous trees and also produced some roof and siding damage to a few homes. Additionally, a pickup truck was picked up and moved 6 feet by the strong winds. This is how the storm looked on radar shortly after touchdown.

1a

 

The QLCS (quasi-linear convective system) contained a somewhat unimpressive couplet (rotation) through the tornado’s life. While occasionally exceeding 50 knots of gate-to-gate Delta-V it was generally not particularly intense.

What is impressive is that for 10 minutes – this tornado produced a clear tornado debris signature on radar. You can see in the above image near North Chemung depressed correlation coefficient and near-zero ZDR – all coincident with an area of rotation and sufficiently high Z (reflectivity).

2a

3a

4a

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The tornado debris signature on radar appeared from 2309 UTC and disappeared by 2323 UTC. It was on the lowest elevation slice and the debris reached a height of 6,000 ft AGL at one point. What is so concerning about this is that the signature was completely missed by the National Weather Service. No tornado warning was issued for Chemung County, NY.

The Severe Thunderstorm Warning in effect for Chemung County contained no mention of possible tornadoes, no enhanced wording about more extreme wind damage, and in fact was a fairly boilerplate warning for a large geographic area including parts of 6 counties.

This isn’t the first time the NWS has “missed” a tornado debris signature which is, in fact, confirmation of a tornado touchdown. The Revere tornado this July is one example and Lancaster County PA in 2012. Both of these examples are tornadoes that occurred with no warning. Other tornadoes in the northeastern U.S. that were covered by tornado warnings have occurred with no mention of tornado confirmation by the TDS in statements (May 2013 near Albany). Earlier this year – the NWS in Albany did mention a TDS which is the first mention, to my knowledge, in this area.

Given how many tornado signatures on radar in the northeast are fairly “borderline” – dual pol and tornado debris signatures can provide the information needed to pull the trigger. Even weak tornadoes a fair distance from the radar site have produced debris signatures around here!

While a TDS can’t provide lead time for the initial touchdown it can certainly give lead time to people living farther down a tornado’s path. If it’s a training issue or something like that within the NWS – we need to fix it! I also implore television meteorologists to become more comfortable interpreting dual pol products. It is certainly possible now to give viewers a “confirmation” of a tornado without someone actually having to see it. Extra urgency in coverage with specific mention of debris being lofted by a tornado can help get people to safety. Being able to explain “what” a TDS is is now just as important as explaining what rotation means on radar to viewers – particularly in New England where tornadoes are relatively infrequent.

We have another weapon in our meteorological arsenal – let’s use it and use it well! We should educate the public about what radar indicated/radar confirmed means. We should be very clear and unambiguous about what a TDS means and we should get the word out as soon as possible. If it can’t make it into a NWS statement in a timely – put it out on NWS Chat! If some meteorologists at the NWS aren’t using dual pol products during severe weather operations – they need to start and start now!

The lack of a warning west of Binghamton last week with evidence of a confirmed tornado available via radar is completely unacceptable. We can do better and I’m sure we will.

A Snowy Winter? Quite Possibly!

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With weeks and weeks of weather boredom we were talking in the weather center yesterday about the Blizzard of 2013. Our thundersnow reminiscing during August is a clear sign that we need some weather excitement in our lives!

Naturally, one has to wonder what the upcoming winter season will bring to Connecticut. If you love winter cold and snow you may be in luck! Of course, all 6-month forecast caveats (and there are many) apply here. 

The main driver of the global circulation is frequently the El Nino-Southern Oscillation. Locally, there is a correlation between ENSO state and the amount of snow we get in a winter. Generally, a strong La Nina or very strong El Nino is bad for snow-lovers. A weak/moderate El Nino is generally most favorable for a snowier than average winter. 

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Presently, above normal sea surface temperatures are present in the equatorial Pacific and the Climate Prediction Center gives El Nino a 2 out of 3 chance for developing by early winter. Additionally, they say a strong El Nino is unlikely. That’s good news!

At least for the time being, a warm pool of water in the Gulf of Alaska is also present. If this can have some staying power a -EPO is favored which can really help deliver the cold (EPO is a better predictor of temperature in southern New England than the famous NAO). This can certainly change quickly but at least for now it’s a welcome sign. 

Of course, a lot can change. Long range forecasting is exceptionally challenging and can be wildly inaccurate. That said, there is some skill (i.e. better than chance/climatology) in picking out global signals that have a correlation to local weather variables (seasonal snowfall, precipitation, temperature, etc.).  We’re only a few months away from waxing our skis and heading north – let’s cross our fingers for a big winter!