Post mortem severe talk

[ORH_wxman]

I thought I'd start this thread up for some talk on how today's setup produced so prolifically. Its probably the most severe outbreak for New England since May 1998...maybe I'm missing one that could be as severe in between those two but it escapes me right now.

Yesterday and the day before we were talking about how this event could actually be one of the rare setups where we get some pretty decent severe weather in SNE...there were concerns still however.

We listed the pros:

1. Very nice shear, especially directional (for SNE standards esp) which could lead to some discrete supercells

2. Remnant EML moving in (for excellent mid-level lapse rates)...relatively rare for New England

3. Good timing (potentially) for the prefrontal trough

Potential cons:

1. Early morning convection mucking up sfc heating?

2. Dew points not as high as forecast

As we got into midday today, we already saw cells firing up in the Hudson Valley and E NY and the early morning convective cloud debris cleared right out allowing for good sfc heating. The winds were quite backed out ahead of them, even more than models forecasted. We saw a lot of winds almost out of the due south at the surface. We had dew points pooled with even 71-72F type dew points reported from HFD to BAF/CEF areas and around 70F up into EEN and SW NH. We had said we'd probably get some good action if dews could even just be in the 68-70F range and we managed to surpass that...it resulted in ML CAPEs between 3000-4000 j/kg which was even better than model forecasts. Here in SNE, we often see the reverse where models will overdue the instability and favorable parameters, but in this case, it was actually a bit better than a lot of models showed in the 24-36 hours leading up to this.

I'm sure I'm missing some other stuff, so hopefully we can use this thread to discuss it some. Ekster made a comment earlier in the big thread "add another case into the EML paper".

Thoughts/comments welcome.

[HoarfrostHubb]

Folks were mentioning the EML a few days ago and that was a factor.

High dews helped trigger early convection, setting the stage for the big show?

[Typhoon Tip]

Good thread....

I'd suggest this is a bit worse, however - fatalities now 5 and may grow as some unaccounted fors are out there... Some arial footage looks like F3 damage... But, eh, don't want to start and arguement about it either - how the heck does one quantify anyway.

Why: I believe it was the establishment of a llv jet prior to the arrival of the storm clusters from down the Mohawk Trail. The first cell to encounter this lower level wind field (22kts from the SSW up underneath WNW at 700mb is a heftier helicity than we are use to around here) was a cell nearing EEN, which quickly evolved a gated return beneath meso and tripped tor warn. Other cells started following suit one after another. I noticed that the wind vectors were stronger east of PSF, where the most intense verications took place.

None of this came as a shock to me because the 0-3km helicity as an expectation was heavily addressed by those posting hodos, but also ... I observed this myself shortly after noon, when I posted about the 90/70 evolving with trees whipping around in the wind. This was a disconcerting condition for cells in today's type of deep layer, to then have to figure what they would do when the encountered this low level flow.

Btw, another funnel cloud and tor warn took place late up between FIT and Ayer where I am, and it was 72/72 at both locations - but again, prior to the storm coming through the winds began gusting from the SSW.

Today is a clearly an intersect of SBCAPE, MUCAPE (EML notwithstanding), and shear in the right proportions.

[HoarfrostHubb]

Good thread....

I'd suggest this is a bit worse, however - fatalities now 5 and may grow as some unaccounted fors are out there... Some arial footage looks like F3 damage... But, eh, don't want to start and arguement about it either - how the heck does one quantify anyway.

Why: I believe it was the establishment of a llv jet prior to the arrival of the storm clusters from down the Mohawk Trail. The first cell to encounter this lower level wind field (22kts from the SSW up underneath WNW at 700mb is a heftier helicity than we are use to around here) was a cell nearing EEN, which quickly evolved a gated return beneath meso and tripped tor warn. Other cells started following suit one after another. I noticed that the wind vectors were stronger east of PSF, where the most intense verications took place.

None of this came as a shock to me because the 0-3km helicity as an expectation was heavily addressed by those posting hodos, but also ... I observed this myself shortly after noon, when I posted about the 90/70 evolving with trees whipping around in the wind. This was a disconcerting condition for cells in today's type of deep layer, to then have to figure what they would do when the encountered this low level flow.

Btw, another funnel cloud and tor warn took place late up between FIT and Ayer where I am, and it was 72/72 at both locations - but again, prior to the storm coming through the winds began gusting from the SSW.

Today is a clearly an intersect of SBCAPE, MUCAPE (EML notwithstanding), and shear in the right proportions.

Not surprised... sky was crazy then

[TalcottWx]

Well when one looks at the events this afternoon you can piece together a puzzle.

Best shear was definitely further north closer to the low, so was the lift. However not necessarily the most opportune heating because the further NW you go, the earlier the trigger was going to be pulled.

The first thing we saw was those those storms firing up over NY State and far NW NNE. Those areas struggled somewhat because they didn't really have the chance to destabilize like others. After that series of warm front convection either fired up/waned off we were able to clear out central and southern new england and that combined with the good wind direction for dp pooling allowed us to reach maximum instability. The cap and EML also kept us from firing off until the substantial trigger in the prefrontal trough came through. It was all a perfect combination between noho-worcester. It was perfect timing in that region for substantial severe weather and there was no real issues with the forecast that could hamper it. We overcame dews, clouds, and the dry air was proved to be no match for our dynamics. I think the true reason the SPC waited for that hour after putting up the WW's was that they wanted to make sure the storms would actually fire and not be hampered by the dry air. Once they got going they knew the threat was real and posted the tor watch. I think in other areas of the country that tor watch would have been posted much earlier but the memories of the double tor watch weekend definitely made them a bit careful on the trigger.

After the storms maximized their potential in central mass, there was the question as to why storms didn't fire as substantially south into CT. I think that area was further from the dynamics,shear, and trigger that was further south. Maybe that helped the cap hold long enough where the storms fired up too late. I actually think the storms in CT were likely only triggered because of outflow boundaries from the storms over orh/cef.

As the evening progressed the storms weakened as they entered eastern mass, predicatable. Probably some CINH and maybe loss of instability due to all the cirrus the filtered over the area for hours and hours. As night fell the storms became elevated monsters and they actually managed to take up some rotation due to the shear still available to tap into.

All in all this day was a real treat for many and helped maximize the severe potential all over SNE except for the south coast, cape, islands.

I think the NWS does face some questions due to their lack of a tor warning on the springfield cell. I was also extremely disappointed with the outlooks and afd prior to this once in years event.

[CoastalWx]

I saved some data and will post more tomorrow, but this really had the classic setup per Mike Ekster and Peter Banacos EML paper. The turning with height was superb..I mean classic. The question was if we can get any debris cloud out of here for strong heating and we did. Lack of upstream convection also helped maintain lapse rates...a problem that we sometimes have.

Perhaps storm interaction and low level helicity enhancement occurred in the CT valley. Once that tor was established..it had all the elements to maintain itself as it headed into ORH county. These parameters were comparable to some of the outbreaks earlier in the season.

[Ed Lizard]

Abstract of EML paper, anyone know if a free version is available?

http://journals.ametsoc.org/doi/abs/10.1175/2010WAF2222363.1

[Amped]

All those ingredients were in NYC too.

[TalcottWx]

All those ingredients were in NYC too.

You guys were too far from the low... hell we thought we might be at one point

[weatherwiz]

Sometime within the next few days I think I'll do a write up or something...maybe Friday. Just need a few days to freaking relax and clear my head.

[Hoosier]

The forecast soundings were like something you'd see around Springfield, Illinois...not Springfield, Mass. Once it became clear that debris clouds weren't much of a problem and shear was in place (and apparently underforecast like several events this year), I had a feeling that something significant would happen. Only question was whether things would try to get too clustered/linear and cut down the sig tor threat a bit.

Pretty impressive event for New England and a good example that the atmosphere doesn't care about location when the parameters line up favorably with enough forcing.

On another note...I thought the Midwest severe threads moved quickly but you guys took it to the next level.

[TalcottWx]

Sometime within the next few days I think I'll do a write up or something...maybe Friday. Just need a few days to freaking relax and clear my head.

Start by just going asleep and getting a healthy rest right now

[Amped]

The forecast soundings were like something you'd see around Springfield, Illinois...not Springfield, Mass. Once it became clear that debris clouds weren't much of a problem and shear was in place (and apparently underforecast like several events this year), I had a feeling that something significant would happen. Only question was whether things would try to get too clustered/linear and cut down the sig tor threat a bit.

Pretty impressive event for New England and a good example that the atmosphere doesn't care about location when the parameters line up favorably with enough forcing.

On another note...I thought the Midwest severe threads moved quickly but you guys took it to the next level.

Lack of activity further south probably helped. Nothing to disturb the EML to your southwest. Most of the energy was released over central mass,

[CoastalWx]

FWIW the SREFs did nail those supercell and sig tor parameters.

[Ian]

I've only done rudimentary analysis (here's a small part of it) for sig tornado days around here (Mid-atl into PA) but on a 500/850 lvl alone it was pretty classic as far as tornado days go in a lot of places in similar positioning to low/high heights and whatnot. It looked a lot like our best days just shifted north etc. The uber waves that come every few days since April/winter (except when I need them) are energizing just about everything.

I was thinking you guys (or some of you) would get mod risked, but was favoring western/southern areas, probably per climo to some degree. Would have expected w new eng/down to maybe pa/jersey/nyc 'burbs to be ground zero.I was perhaps only looking with one eye as my area was sort out of the game for the best.

[radarman]

1. Early morning convection mucking up sfc heating?

2. Dew points not as high as forecast

Great summary. The pros got better on the models with time.

Early morning convection and DPs I think we all consider major nowcast items around here... When I woke up to clear skies, and DPs in the 70s by early afternoon it was game on.

Really a good job by all the mets in here, and some expertise on loan from the severe crew to highlight this potential. I think we all felt the agencies were a little too conservative with their probabilities and wordings, but once bitten twice shy, and I don't hold it against them.

[ORH_wxman]

All those ingredients were in NYC too.

Not totally. I listed timing of the pre-frontal trough as one of the elements and I think there it came in a tad too early. One other thing was the deeper shear to help maintain updrafts was a little less down there. Those two combined may have been enough to skunk the threat a little bit. Trying to get cells firing too early before max heating and slightly less favorable shear kept them weaker and far fewer.

I'm sure there may have been some other nuances too, but its hard to always pinpoint every single detail. I'm not sure if CINH was a little higher there early on and maybe into CT where they didn't get as much either.

[Sickman]

Past tornado events seemed to have been focused in relatively hillier terrain, i.e. Great Barrington 1995. The CT River Valley always seemed to get spared the worst of the storms, especially as they moved out of the Berkshires. There seemed to be a stabilizing influence, or more accurately, a less unstabilizing influence, that would cause storms to nudge slightly downward in intensity as they entered the valley region. How did that apparently get reversed today? I realize that the setup was a once-in-50-odd-year event, but how did the dynamics end up getting focused in an area that, while not unsuited for such development, is less suited than areas to the west and east?

[ORH_wxman]

Past tornado events seemed to have been focused in relatively hillier terrain, i.e. Great Barrington 1995. The CT River Valley always seemed to get spared the worst of the storms, especially as they moved out of the Berkshires. There seemed to be a stabilizing influence, or more accurately, a less unstabilizing influence, that would cause storms to nudge slightly downward in intensity as they entered the valley region. How did that apparently get reversed today? I realize that the setup was a once-in-50-odd-year event, but how did the dynamics end up getting focused in an area that, while not unsuited for such development, is less suited than areas to the west and east?

The 0-1km/0-3km helicity really increased once you started getting into the valley and then eastward into S ORH county...pretty much right where the strong tornado tracked. I'm sure there were other factors too...the storms didn't get to really blow up as much to the west in E NY perhaps due to the timing of the prefrontal trough.

But with the flow really backed much much more E of the NY border, these storms probably had a chance to take off more than normal. I'm not a 100% expert on this, but I think a rotating updraft will tend to increase in strength/velocity vs a non-rotating updraft, so that extra variable might have really helped the storms take off once they hit that area...esp since it was also already in 3000-4000 j/kg of ML CAPE.

[weatherwiz]

The 0-1km/0-3km helicity really increased once you started getting into the valley and then eastward into S ORH county...pretty much right where the strong tornado tracked. I'm sure there were other factors too...the storms didn't get to really blow up as much to the west in E NY perhaps due to the timing of the prefrontal trough.

But with the flow really backed much much more E of the NY border, these storms probably had a chance to take off more than normal. I'm not a 100% expert on this, but I think a rotating updraft will tend to increase in strength/velocity vs a non-rotating updraft, so that extra variable might have really helped the storms take off once they hit that area...esp since it was also already in 3000-4000 j/kg of ML CAPE.

Great post...this pretty sums up exactly what I was thinking. Today's wind flow/trajectory was PERFECT for backing winds and in the valley locations when you have backing winds helicity is gonig to be increased and models will not pick up on how strong the helicity will actually be.

If you look too, the area was actually JUST east of the strongest EHI values and from what I've heard/read usually the strongest tornadoes occur just to the east of these highest values.

We also got lucky with timing b/c these cells came through during the period of maximized heating/best shear for tornadic development.

Since we didn't get a veered low-level flow that allowed the low-levels to remain moist and kept the dry air in the mid levels from mixing down.

[Sickman]

The 0-1km/0-3km helicity really increased once you started getting into the valley and then eastward into S ORH county...pretty much right where the strong tornado tracked. I'm sure there were other factors too...the storms didn't get to really blow up as much to the west in E NY perhaps due to the timing of the prefrontal trough.

But with the flow really backed much much more E of the NY border, these storms probably had a chance to take off more than normal. I'm not a 100% expert on this, but I think a rotating updraft will tend to increase in strength/velocity vs a non-rotating updraft, so that extra variable might have really helped the storms take off once they hit that area...esp since it was also already in 3000-4000 j/kg of ML CAPE.

Perhaps it's the contrast from a unidirectional linear setup vs. a discrete setup that was the difference here? In other words, a more unimpeded low-level southerly flow was present in the valley, as opposed to the hillier terrain further west, that got these cells really cranking?

[ORH_wxman]

Great post...this pretty sums up exactly what I was thinking. Today's wind flow/trajectory was PERFECT for backing winds and in the valley locations when you have backing winds helicity is gonig to be increased and models will not pick up on how strong the helicity will actually be.

If you look too, the area was actually JUST east of the strongest EHI values and from what I've heard/read usually the strongest tornadoes occur just to the east of these highest values.

We also got lucky with timing b/c these cells came through during the period of maximized heating/best shear for tornadic development.

Since we didn't get a veered low-level flow that allowed the low-levels to remain moist and kept the dry air in the mid levels from mixing down.

The shear definitely was a factor in those storms. Every single cell would begin to go nuts over that area and into central MA...they got 3-4 rounds of that. You'd see it immediately strengthen on radar and then start rotating, even if it was weak rotation. Just about every storm was rotating for a 3-4 hour period in that zone from about AFN/FIT south to the tri-state MA/CT/RI point, W back to BAF and then N up to Greeenfield/Orange area. That zone seemed to have so many storms rotating as soon as they hit there with the max area definitely along the pike region from BAF to about Sturbridge.

I think the extra backed low level flow also helped keep the storms more discrete supercells as they didn't form into a line very quickly like we normally see. It was just cell after cell with occasionally merging into a little cluster, but then it would go back to individual cells again.

[weatherwiz]

The shear definitely was a factor in those storms. Every single cell would begin to go nuts over that area and into central MA...they got 3-4 rounds of that. You'd see it immediately strengthen on radar and then start rotating, even if it was weak rotation. Just about every storm was rotating for a 3-4 hour period in that zone from about AFN/FIT south to the tri-state MA/CT/RI point, W back to BAF and then N up to Greeenfield/Orange area. That zone seemed to have so many storms rotating as soon as they hit there with the max area definitely along the pike region from BAF to about Sturbridge.

I think the extra backed low level flow also helped keep the storms more discrete supercells as they didn't form into a line very quickly like we normally see. It was just cell after cell with occasionally merging into a little cluster, but then it would go back to individual cells again.

Yeah the extra backed flow certainly helped with more discrete development, especially since much of the activity was with the pre-frontal trough...if we saw it with the cold front I think we would have seen more linear action.

Plus the long curved hodos also suggested the potential for more discrete action.

[CT Rain]

Just got back from monson. Wow. Tragic there with whole neighborhoods flattened. Some piles of debris I couldn't event tell what it used to be. Looks like solid ef3 damage to me.

[Arnold214]

Deep layer shear vectors oriented nearly orthogonal to the initiating boundary(ies) as well as the values of bulk deep layer shear itself (at least 50 kt) allowed for discrete supercells to develop and thrive and not just line out. EML was very evident in the very impressive 12z ALB sounding. The EML and associated steep lapse rates not only allows for big CAPE when ample low level moisture is present...but perhaps more importantly...it allows for very anomalous values of normalized CAPE (NCAPE) which is better for explosive storm development. So, you put that type of thermodynamic environment on top of one characterized by strong deep and low level shear you end up with a plains-style outbreak.

[NJHurricane]

All those ingredients were in NYC too.

Was the sheer there as well? I think that was a key component that put interior New England on a separate plateau of convergence of severe ingredients compared to much of the rest of the tornado watch areas of the east coast today.

Remarkable outbreak and thanks to all in this region who have posted timely obs as well as relayed local media reports today.

[free_man]

Not sure of all of the science in-detail, but would be the squeeze play between the upper trough across CA and the high pressure offshore holding on and nosing in be a slept-on factor?. I mentioned that last week and it wasn't addressed much. BOX AFD did mention it Monday. '53 was a perfect example of that, this was fairly good as well.

It seemed with the cool SSTs offshore and the battle going on there between the two, the winds would stay backed around at the sfc more than the models showed. How often do we see medium range models showing a major heat-wave , only to be ruined by backdoor fronts and onshore flow as we got closer? In this case, the squeeze play seemed to help prevent a more westerly wind shift and "drying out" most of us feared.

[ineedsnow]

i cant stop thinking about if i was 10 seconds further ahead on the highway how much worse this could have been for me about to try and get some sleep!

[ineedsnow]

my car has dents and scratches from the debris that was hitting it i always wanted to be close to a tornado but never ever did i think i would be that close

[OSUmetstud]

remarkably similar to the 1953 Worcester tornado 500mb set-up. Also, somewhat similar to the May 31st 1985 tornado outbreak set-up albeit further west. The synoptic depiction was well-modeled for days. However, it was really bizzare how the set-up as modeled seemingly got better in the last 48 hours. All severe factors got better...especially in the hours before the outbreak...deep layer shear, MLCAPE, and low-level helicity sky rocketed.