A South Coast Special

A doctor at Brigham and Women's Hospital in Boston grabs a few chunks of 2.25

A doctor at Brigham and Women’s Hospital in Boston grabs a few chunks of 2.25″ diameter hail.

It’s hard to believe that after egg sized hail fell in Boston Tuesday afternoon it was not the most impressive severe weather event on Tuesday, August 4th. The morning damaging wind storm produced a swath of damage across Long Island and southern New England that is one of the most impressive I’ve seen in years.

Tuesday morning had all the hallmarks of a daybreak severe weather episode. Strong wind shear, steep lapse rates, and an impressive surge of low level moisture. Our computer models struggled with whether or not storms would develop but I decided to be fairly bullish on the severe weather potential anyway the night prior (as did some other local meteorologists). As it turns out – that was the right call. The morning sounding from Chatham (modified for the pre-storm environment at Warwick, RI) shows an uncapped, highly sheared, and highly unstable environment.


With approximately 3,000 joules of CAPE and more than 60 knots of effective bulk shear when storms were able to develop they became beasts. Storm mode was messy with the clusters resembling giant high reflectivity blob, but on doppler radar velocity data showed several pockets of intense damaging wind.

The first such pocket moved across the North Shore of Long Island producing widespread wind damage. When it left the Island a second area of strong winds clipped Groton and Stonington while the core of the wind moved ashore in South County, Rhode Island.

okx11 fatality occurred in Mystic from a falling tree from the northern storm while the southern storm produced an incredible 71 mph wind gust on Great Gull Island (near The Race), a 61 mph wind gust on the Stonington Borough breakwater and widespread wind damage in far southeastern Stonington (Pawcatuck and Greenhaven) as well as Westerly and Charlestown. In Charlestown, an 83 mph wind gust was measured and falling trees injured several campers at Burlingame State Park.

Trees down on Greenhaven Road in Stonington

Trees down on Greenhaven Road in Stonington

KGON 041018Z AUTO 28027G43KT 1 1/2SM R05/4000VP6000FT +TSRA BR BKN014 OVC033 23/21 A2984 RMK AO2 PK WND 24043/1015 LTG DSNT ALQDS RAB10 TSE01B07 P0012 T02280211

KWST 041034Z AUTO 22016G48KT 1/2SM TSRA FG FEW004 BKN012 OVC018 21/19 A2987 RMK AO2 PK WND 23048/1028 VIS 1/4V1 3/4 LTG DSNT ALQDS RAB21 TSB20 P0030 T02110189

Meanwhile, a second cluster of thunderstorms was bringing an exceptional wind storm to portions of the Providence metro area. In terms of damaging straight-line winds the radar signature over Warwick/Cranston was one of the most impressive you’ll see in New England.

box1The first sign of trouble was over western Rhode Island in the town of Coventry. In about 5 minutes the core of the storm exploded – with 65 dBz over at 30,000 feet by 6:12 a.m. Within the next 20 minutes what starts as a relatively benign looking velocity signature in the low levels of the atmosphere turns into a monster with a large core of destructive winds (at least 5 miles wide with >50 knots).


A closeup of the storm over Warwick and Cranston shows just how intense the storm was with a few pixels of radial velocity approaching 80 knots.


As luck would have it this passed very close to TF Green airport where a wind gust of 67 mph was measured as the storm moved through.

KPVD 041034Z AUTO 30027G52KT +TSRA 17/16 A2985 RMK AO2 PK WND 29058/1028 LTG DSNT ALQDS RAB14B29 TSE01B11 P0057 T01720161 RVRNO $

What’s interesting is that this wind occurred about 2 miles south of where radar was picking up the strongest velocity. In fact, the velocity sampled over KPVD was 56 knots (at 1300 ft) which is almost exactly the peak gust measured at the airport was. It stands to reason that areas on the Warwick/Cranston line saw wind gusts up to 90 mph as the storm roared in and the atmosphere was able to efficiently mix to the surface.

Courtesy: WX1BOX Warwick/Cranston RI - N1EGS-John Buco

Courtesy: WX1BOX Warwick/Cranston RI – N1EGS-John Buco

A few takeaways from this event that really stand out.

One, The the Storm Prediction Center frequently doesn’t outlook or issue watches for these “south coast specials”. They’re characterized bya relatively narrow zone of high theta-e air advects north from the ocean resulting in a small area of substantial CAPE near the coast. What’s frustrating is that even though there’s only a small geographic area at risk – the population for that area is HUGE – including Long Island, southern New England, and even the New York City area. A severe thunderstorm watch would have been helpful to increase situational awareness of forecasters (both TV and NWS) around the region.

Two, even though reflectivity imagery didn’t have a classic signature for a widespread destructive wind event – velocity data from both OKX and BOX was spot on in identifying the areas hardest hit. Even a giant blob of reflectivity (as opposed to a well-defined squall line) can produce significant severe winds.

Three, this event shows that true severe thunderstorm events can be just as damaging – if not more than a tornado event. In fact, the 125,000 power outages from this thunderstorm event in Rhode Island was worse than Hurricane Sandy. This event was one of the few around here to verify Severe Thunderstorm Warnings with multiple 50 knot measured gusts. This storm was the real deal. It’s important to differentiate between the run of the mill severe storms that take down a couple diseased tree limbs from the ones that have the potential to produce widespread and life-threatening weather. This is one of our biggest challenges here in southern New England during convection season.

A Nino Roaster?

The Pacific Ocean is on fire. Well, not literally on fire, but it’s pretty damn toasty out there. Chris Farley would be proud of this El Nino. The large mass of unusually warm water in the equatorial Pacific continues to grow and become even warmer – possibly rivaling some of the strongest El Ninos in recent memory.


Computer model forecasts continue to show a strengthening of this El Nino – and most experts I’ve spoken to believe this El Nino will be strong come winter.


The question is – what will a strong El Nino mean for New England? The three most powerful winter El Ninos since 1950 have produced below average snow in Connecticut. In fact, the mean and median snowfall for the top 10 El Nino events is below normal for both Hartford and Bridgeport.

The record 1997-1998 El Nino was accompanied by a mighty dud of a winter. Only 8.9″ of snow fell in Bridgeport (average is 29.0″) and in the Hartford area only 28.7″ of snow fell* (average is 48.4″). The 1982-1983 El Nino which peaked over the winter was only somewhat below normal in terms of snowfall, 46.4″ in Hartford and 23.0″ in Bridgeport. Rounding out the top 3 the winter of 1991-1992 was another dud with 23.6″ of snow in Hartford and 16.5″ in Bridgeport. Awful.

The top 10 El Nino and top 10 La Nina events are all relatively blah when it comes to snowfall.

Top 10 La Nina Events (since 1950)

  • Hartford mean snowfall 46.4″ / median snowfall 41.9″
  • Bridgeport mean snowfall 26.3″ / median snowfall 22.6″

Top 10 El Nino Events (since 1950)

  • Hartford mean snowfall 41.9″ / median snowfall 40.8″
  • Bridgeport mean snowfall 26.0″ / median snowfall 21.5″

Also of interest is that the top 10 El Nino events in Hartford have an average winter temperature above normal. The top 10 events average a winter temperature of 29.5 degrees (median of 29.7 degrees) compared to the 30-year average of 29.1 degrees. Additionally the top 3 El Nino events (’82, ’91, ’97) were all well above average with a mean of 31.5 degrees – more than 2 degrees above normal.


El Nino is only one part of the puzzle. While odds favor a warmer than normal and less-snowy than normal winter in Connecticut meteorologists will likely have their hands full. A strong El Nino will essentially put the subtropical jet stream on steroids. Plenty of moisture and energy will be around for “fun” storms – likely many messy storms with snow, mix, rain, etc. Even a “below normal” winter can produce a big one – remember the Megalopolitan snowstorm of 1983?


*Notes: To compensate for missing snowfall data in the official records I’ve used our weather observer in Collinsville for snow totals and adjusted them by a factor of 0.86 (I got this from comparing the mean snowfall at BDL and Collinsville for available years). This isn’t perfect but it is the best we’ve got. Also, to compute the top 10 El Nino/La Nina I averaged the MEI over December, January and February to come up with a winter ENSO strength. All stats are for ENSO events 1950-present.

Giant Hail in Maine

Courtesy: Bart Haley / Berwick, ME

Courtesy: Bart Haley / Berwick, ME

Getting baseball size chunks of ice to drop out of the sky in New England takes a special kind of storm. That kind of storm blew up over portions of southern New Hampshire and Maine on Sunday.


Not surprisingly, it took a fairly unique environment to produce this giant hail. The most important feature was a remnant plume of elevated mixed layer air that resulted in steep mid level lapse rates across New England. What we mean by this is an unusually steep drop in temperature between about 10,000 and 25,000 feet above our heads. We can quantify this by measuring the temperature difference over certain levels.


Between 700mb and 500mb the lapse rate on the evening Gray, ME weather balloon launch was 7.2 C/km. The Chatham sounding (away from thunderstorms and probably more representative of the pre-storm environment) had a very impressive 7.6 C/km lapse rate. Research by Banacos and Ekster has shown that many significant severe weather events in the northeast occur when an elevated mixed layer is present.

The EML is quite common in the plains – not so common here. With that in place the stage was set for a pretty impressive severe weather event. CAPE on the order of 3,000 j/kg and large CAPE in the hail growth zone (the part of the atmosphere between -10c and -30c) and enough effective wind shear (30 to 35 knots in southern Maine) was enough to give us some hail beasts.


This cross section of the storm from the Gray, ME radar shows the exceptional hail core. 70+ dbz values were up to 27,000 ft AGL and a giant three body scatter spike was present down radial.

Prior to dropping baseballs – radar gave a clear indication that this storm was about to drop some big ice.


On the GYX dual pol products you can see the high reflectivity in the upper left panel (huge TBSS too), while on the upper right you can see the low CC in that hail core. CC values ranged from 0.75 to 0.9 in the lowest part of the hail core along with ZDR (bottom left) well below zero. This is a very solid signature for significant hail – and in this case baseball size hail. Below – you can see the storm at peak intensity at about 20,000 feet above the ground with a giant hail spike accompanied by an 80 dbz pixel!!

80 dbz and giant TBSS at 21,000ft AGL

80 dbz and giant TBSS at 21,000ft AGL

Prior to reaching peak strength the storm exhibited very impressive wet hail growth between -20 and -30c. You can see the depressed CC (indicating mixed phase hydrometeors) way above the freezing level – a clear signature for big hail growth. Also present (not shown) was a large ZDR column indicating a tremendous amount of liquid water being lofted by the storm’s updraft.


GYX 5.1 degree tilt – sampling storm approx 27kft AGL

So that’s the story of the giant Maine hail. Never underestimate a sounding with fat CAPE!

Courtesy: Bart Haley / Berwick, ME

Courtesy: Bart Haley / Berwick, ME

Chance for a Few Strong Storms Wednesday


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.


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!