Weekend Snow? Possible But Not Likely

Slippery roads, icy conditions, nor’easter. Sound familiar? Before we give in to the weather hype that is seemingly ubiquitous on Twitter, Facebook, and some media outlets we should probably take a look at the data and use some meteorology.

ecmwf_apcp_f96_us

All of our computer guidance shows a pretty sizable storm developing off the east coast as a large and amplified trough digs south into the eastern U.S.

Earlier model runs on Sunday and Monday showed a different kind of setup with a strong upper level low swinging through with a classic signal for some snow showers and snow squalls under it as cold air rushed in. I posted the midday Sunday and Monday computer model runs below so you can see the change.

ecmwf_apcp_f150_us

ecmwf_apcp_f132_us

But now that signal as all but disappeared. The energy that digs south from Canada really “digs for oil” and winds up emerging off the coast in the Mid Atlantic – not New England as advertised on Sunday. This setup puts Connecticut between the 2 features of interest which leaves us with a fairly boring weather regime for the weekend with snow possible in the Appalachians and Maine (if the Euro is to be believed).

Snow flurries made sense in the forecasts you saw on Sunday and Monday but it didn’t yesterday and doesn’t today. What we’ll have to watch today is the track of the coastal low and how close to the coast does it get? Winter will come – but right now it looks like we’ll just have to wait a bit longer.

So, Was This Storm a Nor’Easter? Yes – I’ve Changed My Mind

After my post 2 days ago about what constitutes a nor’easter and that I didn’t expect this storm to fit the bill – I’ve changed my mind!

As late as midday yesterday our computer models were showing a large storm (area-wise) but a somewhat unimpressive storm in the wind department. The rainfall forecast (amounts and timing) worked out great but the wind exceeded my expectations! The National Weather Service was in the same boat yesterday with no gale warnings or wind advisories prior to the onset of strongest winds to having to post the advisories in the middle of the storm.

It was the nor’easter that wasn’t but turned out to be! Here’s the midday GFS run for wind speeds about a mile above the ground (850mb) valid at 8 p.m. yesterday. It’s only a 12-hour forecast.

gfsNE_850_spd_012

 

As it turned out, vigorous thunderstorm development and the presence of several “meso-lows” (basically, just a fancy term for smaller scale low pressure systems) were able to modulate the wind profile and result in a narrow band of much stronger winds than originally forecast.

Here’s a look at the analysis of winds at 850mb last night and you can see things turned out a bit more impressive than originally forecast.

namNE_850_spd_000

Closer to the surface the difference was even more noticeable. Here’s a forecast sounding for KOKX (where the weather balloons are launched on Long Island) off the GFS model valid at 8 p.m. yesterday.

bufkitprofile

Here’s the analysis off the 00z NAM which is much closer to reality though based off the 00z balloon launch is still a bit underdone (balloon measured winds of 55 knots at 901 mb and 50 knots as low as 935mb).

bufkitprofileA closer look reveals even the temperature profile on the analysis (and certainly the 12 hour forecast) was inadequate to describe the structure of the boundary layer.

OKX (2)

The inversion starts quite a bit higher (around 880mb) than modeled. The combination of a stronger wind profile and a deeper mixed layer lead to a much windier storm than originally expected. Thankfully, the winds weren’t strong enough to cause any significant issues here in Connecticut besides sporadic power outages. If nothing else the storm was a fantastic one to fall asleep to last night with strong wind gusts, periods of heavy rain, and occasional thunder and lightning.

The final verdict on this one: nor’easter and overperformer. Lessons learned? For a storm with such vigorous convection nearby (and in some cases overhead) some of the higher resolution non-hydrostatic models deserve some extra love. It’s easy to dismiss them since they seem to always produce funky and extreme solutions – but in an overly dynamic storm they may be the way to go!

 

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

Bzb4QH0CYAAk3xT

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

Supercelltobowecho

 

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

848

 

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?

1690017_850897881610510_5053306368029620182_n

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!