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Low topped squall line overnight Wednesday into Thursday

weatherwiz

By weatherwiz,
in New England

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OceanStWx

OceanStWx

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State College did a nice job with that tornado warning. 

 

I thought the performance down in NC was a bit troublesome though - huge FAR including a busted tornado emergency. Looks like no lead time on the fatal Waverly storm either. 

 

RAH dropped like 21 TORs. A buddy at ILM issued 4 and is pissed that none have come up with damage so far.

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HoarfrostHubb

HoarfrostHubb

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Quasi-linear convective system.

Sometimes also called a line echo wave pattern (LEWP), it's when your squall line has breaks or protuberances that push out from the main line. Usually a sign of some pretty strong shear in addition to the slab lifting.

Sorta like ocean waves as seen from above crashing on a beach? Neat

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CT Rain

CT Rain

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RAH dropped like 21 TORs. A buddy at ILM issued 4 and is pissed that none have come up with damage so far.

 

A lot of the ones in Raleigh were a bit puzzling. There were some really clear ones - like the one in Granville Co that did the damage - but some of the others were pretty meh.

 

I wonder what helped the spinners over VA but held them back over NC? Warm front up there?

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OceanStWx

OceanStWx

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A lot of the ones in Raleigh were a bit puzzling. There were some really clear ones - like the one in Granville Co that did the damage - but some of the others were pretty meh.

 

I wonder what helped the spinners over VA but held them back over NC? Warm front up there?

 

Subtle secondary warm front it looks like. You can see it in a few of the meso fields, like theta-e and MLCAPE. Plus I think the early convection may have left behind some boundaries too.

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TalcottWx

TalcottWx

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For the novice weenies last night is usually how we get our severe events in Eastern MA. Elevated instability is our best and usually only hope. When we have significant severe and shear it usually results in a south, southeast wind direction in Southern New England which floods areas east of ORH with a marine and stabilized airmass that absolutely destroys surfaced based convection at our latitude.

 

Last night had strong southerly winds but the advection of warm air, humid airmass aloft, theta e, etc creates the elevated instability aloft that negates any problems with relying on surface based instability. One of the great examples is the day of the Springfield/Brimfield significant tornados that were originally discrete. Later on that night we had a wonderful lightning show and gusty winds as a result of the elevated instability that remained into the night time hours and we did well with the linear storm mode that developed. MUCape is the best cape as we saw last night. Great lightning.

 

There are even cases of significant severe weather events in the plains with zero surface based instability. They even produce numerous tornadoes on occasion. It is more rare though compared to the surface based events.

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TalcottWx

TalcottWx

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I recall a severe event last year (I'm awful with dates) that resulted in a line of storms, some discrete, some linear that had a svr watch posted almost all the way east to BOS. I remember Tip pointing out the fact that the CU fields were simply suffocated as they developed. During the beginning of severe events you sometimes have the EML (elevated mixing layer) that delays CU production and allows the surface to maximize surface heating. When you get to a certain point in the afternoon you can actually make out the extent of the marine layer's punch into the area by viewing the visible satellite. Usually you will have a CU field start to develop in the afternoon and a clear line between the marine air-mass and the destabilized airmass. It's almost textbook every single time. There will be the CU field and then south and south east of it clear skies and quick pop up CU that is quickly devoured by the convective inhibition or CINH. Many of those large severe events I can actually smell the ocean air and you will be able to track it by the dewpoint and temperature gradients over the area. It's fascinating. I'd love to go back and find some of the visible pictures of supercells out near the berks while we have clear skies and struggle to even develop one cloud.

 

I sometimes make the mistake of trying to talk myself out of the fact that we are screwed as I watch these monster cells approach then they collapse every single time when they hit the wall of marine air. It's painful. So close yet so far. Scott is always great at helping to point out these issues during our severe events for those in our area and portions of SNE aforementioned.

 

On rare occasions like the day of the Springfield cell you will have enough elevated instability to maintain the cells despite our lack of surface instability. It happens, but it is rare. It takes an anomalous setup like last night for it to happen. Hell, it is February for God's sake.

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CT Valley Snowman

CT Valley Snowman

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Just put together a blog post on last night's storms in CT. http://www.ryanhanrahan.com/2016/02/25/rare-february-severe-thunderstorms/

Nice write up. I thought the best gusts here were with the discreet stuff, seemed like instability was maximized just ahead of the line with the cranking LLJ and cells ripping north from LI sound. Winds here probably hit around 50 with the discreet and like 40 with the main line. Awesome job describing the soundings, really cool stuff.

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ryanjn

ryanjn

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Yeah as sbos was saying about elevated instability, it's the dynamic driven events with elevated instability that have the ability to peak after dark because they are not dependent on diabatic heating. With a near inversion/isothermal layer like we had last night below 850mb, usually it's difficult to get winds down to the surface because as the cool air sinks it eventually hits air as cool as it and the homogeneity prevents the air from sinking farther. A steepl apse rates goes both ways in terms of rising air or sinking air. I'm looking at a sounding for the Taunton area around 9z just before storms hit and there's a brief but steep adiabatic lapse rate between 750-700mb and a constant 13-14C 850 and below. At 12z the lapse rate is a bit steeper, relative to what it was hours earlier, and was probably enough to help that llvl jet (about 65kts even as low as 925mb in places) reach the surface. I'm assuming this was the case in most areas in the warm sector. 

 

A lot of forced events don't have a lot of lightning like we saw with especially storms between RI and Boston. Figuring out which storms will be prolific lightning producers and which ones will not has always eluded me, but I think the steeper the lapse rate between -10C and -30C the better. Lapse rates were relatively steep in that area for New England, around 7C/KM I think, and the dynamics and amount of kinetic energy in the storms allowed for plenty of graupel interaction to allow charge separation. Flashes were "hot" and flickering with a handful of return strokes in our storms though, which was surprising because most of the cold season storms I've witnessed the flashes are "cold" and no there are no return strokes. 

Although we didn't have a blatant inversion, most storms that are elevated produce higher amounts of IC than CG. It's almost like the top of the inversion is the ground relative to the storm in a way. Once that isothermal layer diminished as storms moved through, especially SE MA and RI, we saw storms with higher amounts of CG strikes.

If an inversion is in place, however,  the thunder will sound distant and overhead from IC flashes because the sound bounces off the inversion and stays mostly above the inversion. If there's a CG strike the sound can be deflected off the inversion and that sort of creates an effect where the thunder is louder/quieter in areas you wouldn't think it'd be. 

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ryanjn

ryanjn

Posted
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I just got back from a drive, saw a few branches down on 125 in Andover/North Andover, and a tree down on Andover st in North Andover, half mile from Merrimack College. I'm sure there were more but it was dark out so couldn't see a ton.

Feb 26, 2010 wind event we had widespread 60-70mph winds and a lot of trees down, especially conifers. Wind damage certainly wasn't as widespread as that event (here anyway) and that event I think the high winds lasted a bit longer if I remember correctly. Comparing it to that event I'd say winds were about 10mph less last night.Luckily foliage wasn't an issue so there was prob significantly less damage than otherwise would be.

KLWM is a few miles NW of me and was just west of the strongest cores around 3-3:30am. They reported a 45mph gust, so I'd estimate the winds just east under the strongest cells to be 50-55mph and sustained 25mph with a few 30-35mph sustained for a time. 

Not as much CG activity here but we certainly had a few close ones mixed in. Prob 4-8 flashes a minute at the height of the activity here, with a few power flashes mixed in. 

Overall a rare an awesome spectacle, despite not even having the strongest storms of the event in my area. 

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ryanjn

ryanjn

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"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."

 

I noticed this effect too. I assumed it was because the storms were moving so quickly there was a slight lag in the precip. Also the winds were higher a little above the surface so higher echoes observed were an artifact of llvl jet pushing the rain farther ahead of the rain closer to the ground. Any thoughts on this?

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Ginx snewx

Ginx snewx

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"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."

I noticed this effect too. I assumed it was because the storms were moving so quickly there was a slight lag in the precip. Also the winds were higher a little above the surface so higher echoes observed were an artifact of llvl jet pushing the rain farther ahead of the rain closer to the ground. Any thoughts on this?

I have noticed many times this lag between winds on radar and ground wind. I always thought exactly what you described above. It was most noticeable in the Feb 13 Blizzard but again in March 13 retro. A similar situation occurred with Irene.
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