Chance for a Few Strong Storms Wednesday

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Unlike last week when we were expecting a medium/high impact severe weather event across the state tomorrow’s severe weather potential is quite a bit lower. There’s a few reasons for this.

First, let’s take a look at the setup way above our heads halfway through the troposphere around 11 a.m.

gfsNE_500_avort_021

We have a fairly powerful upper level trough moving through (notice the dip in the black lines) across the northeast. At the same time, a disturbance known as a shortwave is overhead in southern New England racing to the northeast. Ahead of this shortwave is where air will typically rise and behind it is where air will typically sink. With the early arrival of this shortwave we can expect to see sinking air/subsidence during the midday and early afternoon following a period of morning rain and even some thunder.

So – where’s the severe weather threat? In the morning (during the AM commute) we could see a pretty could downpour and lightning show in a few towns. Behind this is where the severe weather threat exists – but it’s far from a certainty. You can see on our computer models a very large discrepancy in how the atmosphere will look late Wednesday afternoon. Below you will find forecast soundings for Hartford from the GFS and the NAM.

bufkitprofile namThe GFS (top) would indicate little if any severe weather potential. Much drier air filters in from the west resulting in a dramatic drop in instability. The NAM, however, keeps a fair amount of moisture around in the lowest 3km of the atmosphere which results in a much more unstable profile. To visualize that look at the difference between the yellow line and the red lines above.

CAPE is defined as the area between a parcel and the environmental temperature (think integral – calculus fans!) The more area between the yellow line (parcel) and red line (environmental temperature) the more instability. This makes sense because air parcels warmer than their environment will rise – and it will rise more quickly the greater that difference is.

So where does that leave us tomorrow? The NAM solution is intriguing because it generates a sufficient amount of CAPE and the NAM also has some substantial wind shear which can help organize thunderstorms and also favor supercells. More than 30 knots of deep layer shear along with impressive low level veering (winds south at the surface and westerly 3km up) is concerning.

My gut feeling is that the GFS solution – the uneventful one – will be most correct. As that morning shortwave moves through we’ll be left with subsidence that should limit afternoon storm coverage. Additionally, our short range ensembles (SREFs) which I find useful in the warm season, show very meager CAPE during the afternoon – generally <1000 j/kg.

So there you have it. At this point I’m expecting a low impact event which would means isolated coverage for strong storms – and of the storms that form borderline severe weather rather than high-end severe weather would be favored. If the more vigorous solutions (like the NAM) come to fruition then we will have to reevaluate tomorrow morning.

An Uncertain Weather Future

Earlier today I tweeted out something to the effect of the forecast confidence for Friday/Saturday is something just a few pegs above magic 8 ball confidence. That wouldn’t both me so much – except Saturday is July 4th!

So what’s the deal? Here’s a really basic look at the weather pattern on Friday and Saturday.

Custom Map 2

So there you have it – a close call. It’s nearly certain our computer models will flip back and forth several times between now and the end of the week. One way we try to look at the forecast uncertainty/certainty is to look at “ensembles”. The way this works is that the initial conditions of each computer model is tweaked a bit and the model is run to show you a range of possible solutions. When most of the solutions are the same – confidence is high. When there’s a tremendous amount of spread- confidence in the forecast is low. This weekend? Well, you guess it – low!

f126This shows a number of different solutions ranging from a sunny 4th to a rainy 4th on these different GFS ensemble members. The European ensembles are similar with about 1 in 4 members showing a wet solution on Saturday.

So there you have it. Saying I know what will happen on Saturday is not something I’ll do. For now, we’ll play things optimistically but I really wouldn’t be surprised if we have to deal with some weather issues. Bottom line – stay tuned to the weekend forecast!

Powerful Storm Sweeps Across Southern Connecticut

Damage in Wallingford

Damage in Wallingford

Wow – what an afternoon! For a few days we knew today had the potential to be very active and that’s indeed what happened. A combination of adequate instability and unusually strong wind shear (for Connecticut) resulted in a widespread damaging windstorm from Ridgefield to Jewett City.

The damage in Ridgefield was quite substantial. You can see an area of 60 knot winds showing up on radar only about 3,300 feet ARL.

ridgefield

The storm continued to produce damage over Redding, Monroe, Shelton, and Trumbull and then really picked up steam just north of New Haven. Over Hamden and Bethany at 4:21 p.m. you can see a noticeable eastward surge/bulge in the reflectivity likely due to a descending rear inflow jet.

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By 4:35 p.m. an area of strong outbound velocities (in excess of 50 knots) near the Wallingford/Durham line had developed as the radar was sampling the RIJ quite well.

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Most of the damage appears to be from this RIJ that descended to the ground at the lead edge of this “bow”. By the time the bow was over East Haddam and Salem the rear inflow jet was quite clear on radar (it probably would have been clear earlier but the jet was blowing perpendicular to the radar beam) with winds over 70 knots around 4,000 feet above the ground!

ehaddam

At the height of the storm near 60,000 customers were without power with Ridgefield, Newtown, Durham, Chester, Killingworth, Haddam, East Haddam, Portland, and East Hampton being some of the hardest hit towns. The damage even continued farther east into Lisbon where numerous trees were knocked down.

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The setup for today’s severe weather was a classic one for southern New England.  A plume of remnant elevated mixed layer air kept mid level lapse rates steep along with a strongly sheared wind profile (effective bulk shear values approached 50 knots!).

bufkitprofile

Big Severe Weather Day Possible Tuesday

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The ingredients appear to be there for a major severe weather event on Tuesday. I have to say this has me intrigued! As an upper level system swings through northern New England and southern Quebec we will see an impressive combination of strong shear and strong instability develop over Connecticut.

bufkitprofile

You can see a very moist layer around 900 mb (dew points of near +20C) with very impressive wind shear (southwesterly winds at the surface veering to westerly and rapidly increasing with height). Seeing mixed layer CAPE in excess of 2,000 j/kg co-located with more than 50 knots of shear is pretty unusual around here. Normally it’s one or the other – getting both is tough.

We’re also seeing a remnant Elevated Mixed Layer (EML) move through early in the day with steep mid level lapse rates. It’s unclear exactly how this will evolve by Tuesday but it’s worth watching.

All severe hazards are possible on Tuesday including large hail, damaging winds, and tornadoes. A lot can change in the next day or so but this is worth keeping an eye on.

Remarkable February Cold

Following a relentless cold pattern across the northeastern U.S. this past month will go down in history as the coldest on record for both major climate sites in Connecticut (Hartford area and Bridgeport).

Bridgeport – Monthly Records

  1. February 2015 – 19.9 degrees
  2. January 2005 – 21.9 degrees
  3. January 1981 – 22.1 degrees

Average February Temperature – 32.4 degrees

Hartford Area – Monthly Records

  1. February 2015 – 16.1 degrees
  2. February 1934 – 16.5 degrees
  3. January 1970 – 16.8 degrees

Average February Temperature – 29.7 degrees

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The large-scale flow across the northern hemispheric was remarkably consistent through the month and remarkably cold for southern New England! You  can see large ridging over the western US, Alaska, Bering Strait, and Kamchatka in eastern Russia. This -EPO pattern essentially allowed a continuous feed of Arctic air into New England with a giant drop in the jet stream and cross polar flow.

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It shouldn’t come as much of a surprise that the only substantial “cold” anomalies at the surface across the northern hemisphere were right here in the eastern U.S. and eastern Canada.

One thing that did come to mind when we were breaking the record is that using “months” as cut-offs for coldest periods is a bit arbitrary. What if you had an even more impressive ~30 day period of cold centered between January 15 and February 15? You wouldn’t break any records even though the cold was just as impressive. As it turns out if you go and look at the coldest 28 day stretches this one wasn’t the coldest on record – in Hartford’s case not by a long shot.

Top 3 Coldest 28 day stretches / Hartford Area (end date indicated, multiple days in a year excluded)

  • 2/13/1961 – 12.1 degrees
  • 1/16/1981 – 12.9 degrees
  • 2/11/1948 – 13.6 degrees

In fact this year, the coldest 28-day stretch ended 3/1/2015 with an average temperature of 15.8 degrees. That was actually ties the 2004 cold outbreak with a 28-day mean of 15.8 degrees ending 2/3/2004.

In Bridgeport, the coldest 28 day stretch occurred in 2004 with an average temperature of 18.7 degrees ending 2/3/2004 with the 2015 stretch coming in more than a degree higher at 19.8 degrees (ending 3/1/2015).

Bottom line is that statistics can always be found to make something seem more or less impressive than it really was. Make no mistake that breaking the coldest month record was pretty wild – but it’s not unprecedented. Other, colder, 28-day stretches have occurred but they didn’t fall neatly in the Gregorian calendar like the 2015 cold snap did.