SNE Svr Wx 7/26 - What went wrong?

[vortex95]

Comments on the below welcome....

Couple things I noticed...the mid level lapse rates over the entire area were poor.

In some cases close to the moist adiabatic lapse rate of 5 C/km. Here are the lapse

rates for 00z.

http://home.comcast..../lapserates.jpg

.5 C/km up or down is huge, given the dry adiabatic lapse rate is 9.8 C/km. Poor lapse rates really knock

down the CAPE, and there is no mid-level CAPE in an elevated mixed layer (EML) to tap for nocturnal

convection. The heavy showers that moved over VT/NH during the evening had zero lightning, evidence

of the lack of strong enough updrafts for sufficient charge separation in the clouds. Just low topped,

tropical-like heavy showers.

I also noticed on the CHH and esp. the OKX sounding for 00z, rather strong CINH (convective inhibition or cap).

See table at bottom here:

http://home.comcast....OKXsounding.gif

OKX's sfc based CINH was -221 and mixed layer CINH was -116...far too strong for even established strong

convection to challenge. This seems to be the main reason the squall line weakened once over NYC

and swrn CT. Parcels no longer could sustain buoyancy, thus the tstm updrafts collapsed. Doesn't matter

how much CAPE you have above the cap, if parcels can not reach the LFC (level of free convection), then

say goodbye to tstms. In addition, the 00z 850 temp at OKX was 22 C...that's awfully warm and basically is a

cap for areas near sea level. A cap can be at 850, not just 700. The convective sfc temp for the 00z OKX

sounding was 95 F and it didn't even get that high during max heating. So we actually had *too* much

WAA (warm air advection)!

We all got duped. SPC had the MDT risk, BOX put out a flash flood watch, models showed widespread

precip, and MOS tstm POPs were very high over all of SNE...go figure! I guess we have to remember that

the forecast models are just that, MODELS of the atmosphere, not the actual, and even today, they are

subject to large errors, even in the short term. The squall line Thu aftn started out very promising in wrn

NY and PA, and everything seem to unfolding on schedule, and then it all fell apart. There was a lot of

wind damage in PA/NY, but no where near what I was expecting. I really thought this would be a strong

derecho or even another super derecho.

[free_man]

Interesting. I was not expecting a derecho but I had in mind a decent line forming across w ma/ct and moving east through orh/pvd by 2am. (concerning the northern sne extent )

It may have been beat to death in the other thread, did not read entirely, but did the initiation by 3-5pm over pa/ny promote cin or "rob" areas further ne?

[Chumpson]

I wouldn't say we got "duped", it just didn't work out the way some people expected for every single location in the MDT risk. One big problem with forecasts is conveying uncertainty and understanding the range of (likely) outcomes. In this case, at least with the forecasts through the 1300Z outlook, there was no SPC expectation of a "super derecho" or anything of the like. The MDT risk was driven by the 45% wind forecast, and that part appeared to verify quite well across the vast majority of the outlook area. The "significant" wind area looks like it was an over-forecast, though it's one of the least understood and predictable aspects of the convective outlooks (sighail and sigtors are generally easier to forecast).

Regarding the meteorology of the event, the midlevel lapse rates were rather poor in the 550-350 mb layer, but were closer to 7-8 C/km in the 850-550 mb layer in the 00Z OKX sounding. Since the focus here is on the rapid demise of the storms, CIN did appear to be an important player, and most of it was the result of a surface temperature of only 79 F. Modify that sounding for low 90s and there's no CIN and 3500+ J/kg MLCAPE. So, the first suspect appears to be the lack of surface heating that far east. To get a bunch of "significant" severe wind gusts, you generally need exceptional downdraft and precipitation loading profiles (kind of like 6/29), as represented by steep lapse rates, large CAPE, large DCAPE, etc. Or, you need a "decent" thermodynamic profile in combination with plenty of high-momentum flow in the low-mid troposphere. Yesterday had maybe 40-50 kt peak winds and moderate buoyancy, as depicted by the 18z PIT sounding:

Compare the PIT sounding with the 00z OKX:

The biggest difference is slightly weaker midlevel flow, and the stable layer just above the surface. Interestingly, aside from slight backing and

weakening of the 700-500 mb winds, the only warming occurred around 850 mb and not at the surface from 18-00z at OKX:

Midlevel lapse rates did improve a little from 18 to 00z at OKX, but that was likely offset by the lack of any warming of the surface temperatures.

Keep in mind that most of the forecasts were already out long before this information became available. Part of the problem is properly

interpreting what you see in numerical guidance, and the other part of the problem is deciding whether or not it's accurate. The latter is sometimes

relatively easy, and sometimes it's quite difficult. Since I don't know how to extrapolate atmospheric conditions 12-24 hrs into the future better

than our current operational models, this problem will persist.

[Ellinwood]

Two things about the forecast that stood out to me when analyzing the northern extent of the severe risk was 1) the morning convection across NY and New England and 2) a lack of a strong mid-level vort max that would have provided stronger dynamics and better low-level temperature advection. Without the dynamics to promote the height falls, better lapse rates and low-level advection, the atmosphere in the Northeast was not able to sufficiently recover behind the morning clouds and rain.

To add... in the morning after the convection had gone through it was evident that the warm front was fairly diffuse (EDIT: with respect to winds, anyway), and without that crisp boundary to allow for stronger surface convergence it was more difficult to generate storms ahead of the main line.

[CT Rain]

Comments on the below welcome....

Couple things I noticed...the mid level lapse rates over the entire area were poor.

In some cases close to the moist adiabatic lapse rate of 5 C/km. Here are the lapse

rates for 00z.

http://home.comcast..../lapserates.jpg

.5 C/km up or down is huge, given the dry adiabatic lapse rate is 9.8 C/km. Poor lapse rates really knock

down the CAPE, and there is no mid-level CAPE in an elevated mixed layer (EML) to tap for nocturnal

convection. The heavy showers that moved over VT/NH during the evening had zero lightning, evidence

of the lack of strong enough updrafts for sufficient charge separation in the clouds. Just low topped,

tropical-like heavy showers.

I also noticed on the CHH and esp. the OKX sounding for 00z, rather strong CINH (convective inhibition or cap).

See table at bottom here:

http://home.comcast....OKXsounding.gif

OKX's sfc based CINH was -221 and mixed layer CINH was -116...far too strong for even established strong

convection to challenge. This seems to be the main reason the squall line weakened once over NYC

and swrn CT. Parcels no longer could sustain buoyancy, thus the tstm updrafts collapsed. Doesn't matter

how much CAPE you have above the cap, if parcels can not reach the LFC (level of free convection), then

say goodbye to tstms. In addition, the 00z 850 temp at OKX was 22 C...that's awfully warm and basically is a

cap for areas near sea level. A cap can be at 850, not just 700. The convective sfc temp for the 00z OKX

sounding was 95 F and it didn't even get that high during max heating. So we actually had *too* much

WAA (warm air advection)!

We all got duped. SPC had the MDT risk, BOX put out a flash flood watch, models showed widespread

precip, and MOS tstm POPs were very high over all of SNE...go figure! I guess we have to remember that

the forecast models are just that, MODELS of the atmosphere, not the actual, and even today, they are

subject to large errors, even in the short term. The squall line Thu aftn started out very promising in wrn

NY and PA, and everything seem to unfolding on schedule, and then it all fell apart. There was a lot of

wind damage in PA/NY, but no where near what I was expecting. I really thought this would be a strong

derecho or even another super derecho.

Yeah.... I think this was huge. The NAM especially had been picking up on this for the 18 or 24 hours prior to the event. It had a significant amount of CINH for surface based parcels over most of CT/LI per BUFKIT soundings.

In that 00z OKX soundings 500-700mb lapse rates were 6.3C/KM which isn't great.. but it isn't awful. There was a layer of steeper lapse rates lower than this level in the 600-850mb level which has been discussed in the other thread. That's why you see some pretty solid MUCAPE from parcels at the top of the boundary layer on that sounding... over 3000 j/kg!

It seems to me the storms that formed in W PA/W NY ahead of the main shortwave were accompanied by modest height falls/QG forcing. As the storms traveled east (and accelerated) they ran ahead of the QG assist and though they were fine during the heating of the day in C NY/NE PA they began to run into trouble over SE NY and NJ as the inflow was becoming choked off due to increasing surface based CINH. Had we seen an EML overhead coupled with more surface heating like D.C. had on 6/29 (see the IAD sounding if you want to be wowed) this wouldn't have really been an issue and the storms would have marched right to the coast.

With that 00z OKX sounding I'm a bit surprised the storms fell apart so fast without becoming more elevated? There was plenty of instability to work with at the top of the boundary layer? Was the forcing too marginal to sustain parcels originating above the significant negative area on those soundings (i.e. the cold pool was too shallow to force parcels to the LFC through the CINH)? Had the Great Lakes shortwave ejected east and we had some QG forcing you probably could have maintained the convection a bit longer even if it became elevated in nature.

Here's the 12z PIT sounding. What jumps out at me is the steep lapse rates between 850-700mb.... nearly dry adiabatic! While that looks exciting what we effectively did was create a cap at 850mb with the very warm 850mb temps as HM mentioned. At one point the day prior to the storm the NAM was forecasting 850mb temps of +26C over EWR!

While this certainly wasn't an EML day I don't think poor mid level lapse rates are totally to blame.

[CT Rain]

Great discussion, BTW. Let's keep it going!!!

[Typhoon Tip]

These are all great thoughts. I'd also consider the possibility that the CINH as described over SW zones and NYC area, may have been attributed to a diffused 2ndary warm frontal boundary that was analyzed on the mid afternoon surface depiction from HPC. It extended from NW PA to about NYC. I noted that the convection initialized over NW PA/NE OH right along the western end of that axis, and that the norther extend of the complex never was able to get north of it as the action ripped east through N PA/ S NY.

It effectively - likely - capped the remainder of NY and SNE/C-NE under a unplanned for type of sounding. The stuff in VT/NH that came through with decent rain but apparent weak/no glaciation fits that idea. I suspect the MCS debris in the morning got the differential going as areas S of that axis had superior insolation during the morning.

[CT Rain]

These are all great thoughts. I'd also consider the possibility that the CINH as described over SW zones and NYC area, may have been attributed to a diffused 2ndary warm frontal boundary that was analyzed on the mid afternoon surface depiction from HPC. It extended from NW PA to about NYC. I noted that the convection initialized over NW PA/NE OH right along the western end of that axis, and that the norther extend of the complex never was able to get north of it as the action ripped east through N PA/ S NY.

It effectively - likely - capped the remainder of NY and SNE/C-NE under a unplanned for type of sounding. The stuff in VT/NH that came through with decent rain but apparent weak/no glaciation fits that idea. I suspect the MCS debris in the morning got the differential going as areas S of that axis had superior insolation during the morning.

Eh, the NAM soundings did have it for a while.

I think the low EML over PIT at 12z (certainly by no means the classic EML we normally talk about) was advected east and brought some very warm 850 temps and effectively served as a cap once it reached an area that didn't have the necessary amount of surface heating/moistening and was farthest from the best QG forcing. I'll post some of the bufkit screen grabs when I get to work (on a mac now at home).

[CoastalWx]

I think Ryan brings up a good point. If the storms are accelerating ahead of the dynamics into a slightly more unfavorable environment, that's a problem. If the upper level forcing is not there and the storms are running into a little more cinh updrafts are gonna have trouble sustaining themselves. The thing is though, while I never thought SNE outside of sw areas were really under the gun, the storms still had 3-4k MLCAPE and were already weakening. I agree with Ekster in that the lack of upper level forcing and that warm layer near 500mb probably helped to slow updraft acceleration. The strongest tstms usually have continued updraft acceleration with altitude if I'm not mistaken. If that warm tongue is there, then it's probably best to make sure the upper level venting is there, which in this case seemed lacking

[Typhoon Tip]

I dunno - I wouldn't dismiss the 2ndary warm front - it was analyzed for a reason, and if it is there, it definitely was going stop a more classic SB-CAPE from being realized.

[New England Storm]

I would also have to say one of the big issues was lack of clearing, western Mass &Ct did not clear until like 2:30 ish and PVD at around 3ish. This also helped put a damper on that line staying strong. Also that northern area of convection that many talked about never developed I would guess because of lack of support in the atmosphere?

[CT Rain]

I think Ryan brings up a good point. If the storms are accelerating ahead of the dynamics into a slightly more unfavorable environment, that's a problem. If the upper level forcing is not there and the storms are running into a little more cinh updrafts are gonna have trouble sustaining themselves. The thing is though, while I never thought SNE outside of sw areas were really under the gun, the storms still had 3-4k MLCAPE and were already weakening. I agree with Ekster in that the lack of upper level forcing and that warm layer near 500mb probably helped to slow updraft acceleration. The strongest tstms usually have continued updraft acceleration with altitude if I'm not mistaken. If that warm tongue is there, then it's probably best to make sure the upper level venting is there, which in this case seemed lacking

Take that OKX sounding... 3000 jkg of CAPE! I have a feeling if we actually had a sounding from say POU you probably would have seen quite a bit of CIN under that 850mb warm tongue. If the cold pool is too shallow to force parcels to the LFC you're in trouble.

[NJwinter23]

Finally got a chance to catch up on the thread..a lot of great post-mortem analysis here. I would say the event underperformed to my own expectations once it got to the se NY/NYC/NJ/west CT area, and that's not because I saw barely a 20 mph wind gust in Stamford lol, but going all the way back to a lack of high wind reports even further west. I certainly wouldn't call it a total bust given all of the reports, but I was anticipating a higher end event over all.

What stands out to me most is the talk of earlier arrival (before 00z-03z window that had the forecast best parameters) and outrunning the best synoptic support. With the onset of convection across the Lake Erie area yesterday afternoon, we probably could have anticipated a faster arrival then the 00z-03z. An accelerating cold pool with severe winds of 50-60 mph+ should propagate the line forward with the new updrafts forming. This would be related to outrunning the synoptic support as well, which some have already mentioned was not the greatest to begin with anyway.

The mid-level (700-500) lapse rates were never forecast to be there, but the layer that Arnold described as a possible remnant surface mixed layer at 900-600 was forecast by the nam and i thought that could possibly serve a similar purpose. This may not be the case at all though and it may have fooled me..It did show up on the IAD sounding at 18z, and initially on the kpit 12z sounding..it was likely over much of central PA to when the line moved through...but probably wasnt present across the NYC area (perhaps not having the time to advect in)

[dryslot]

I would also have to say one of the big issues was lack of clearing, western Mass &Ct did not clear until like 2:30 ish and PVD at around 3ish. This also helped put a damper on that line staying strong. Also that northern area of convection that many talked about never developed I would guess because of lack of support in the atmosphere?

Yes, The lingering cloud debris from the overnight into late morning was a big factor as surface temps and dews never really reached there maxes, Upstate NY was still cloud covered late am yesterday, The line as it approached MA/Ct was met by a hostile environment that these cells could not sustain themselves and overcome the CIN, The warm front really never got as far NE as was forcasted as well i believe.

[Tropopause_Fold]

good thread.

couple very simple post-mortem thoughts/observations:

1. some of the hi-res models' simrad products were quite good with the evolution...fwiw...keeping this a S NYS/PA deal and not giving much of anything to SNE other than some showers. might be a foolish approach, but i always keep those products in the back of my mind. i think someone (Scooter?) may have made reference to the SPC WRF also not showing much. just a thought.

2. for our area (SNE), the air mass left a lot to be desired. 24 hours prior it was quite dry and in some areas further N and E actually a bit "cool". it was almost september-like in parts of MA with that stiff NNW wind and Tds near 10C. i know you can prime an environment relatively quickly, but we also know what happens locally when we advect high theta-e air into a departing canadian air mass. more often than not we end up on the losing side of that...or minimally you aren't going to be sitting on a powderkeg locally. so if you don't have the strong forcing, it's going to be tough.

3. speaking to the low-level warm tongue present between 900 and 800 mb...given our poor position relative to the best forcing, that, i assume, was the deciding factor in not getting any discrete activity fired off well in advance of the eventual LEWP. looking at some of the forecast soundings from Wed for spots that were expected to be more squarely warm-sectored like POU, SWF etc, it (the cap) was modeled to be present through ~21 or 22z. lots of CINH on there into late afternoon. had a couple of discrete cells been able to take advantage of the environment over NE PA and the southern hudson valley, the afternoon could have turned out quite differently. but we would have needed some ridiculous surface heating to make it happen given 24-26C temps aloft.

anyway...i don't think the day was a "bust" just that the SPC probs were too aggressive...too far NE.

[NJwinter23]

Eh, the NAM soundings did have it for a while.

I think the low EML over PIT at 12z (certainly by no means the classic EML we normally talk about) was advected east and brought some very warm 850 temps and effectively served as a cap once it reached an area that didn't have the necessary amount of surface heating/moistening and was farthest from the best QG forcing. I'll post some of the bufkit screen grabs when I get to work (on a mac now at home).

Really great explanation in one sentence! Thanks

[HM]

I think a mod needs to bring the conversation from last night in the other thread to this one because a lot of these points (and others) were addressed there. Also, we had Ekster share his thoughts and it would be ashame if they got buried.

[radarman]

With respect to the CINH, in this area we saw numerous elevated showers popping up on radar across the valley, never blossoming nor reaching the ground. Anecdotally I've seen this countless times on days with cap issues.

[CT Rain]

With respect to the CINH, in this area we saw numerous elevated showers popping up on radar across the valley, never blossoming nor reaching the ground. Anecdotally I've seen this countless times on days with cap issues.

Yes I noticed this as well. A lot of times in front of a big line like this the cold pool is enough to break that low level CINH by forcing parcels through the negative area. Low level moistening/QG lift can also help eliminate the CIN. I think in this case the CIN was just too much to overcome.

[forkyfork]

i think the shallow EML also didn't allow for a deep enough cold pool to develop

[wxsniss]

Awesome thread everyone.

Is there any way to visualize CIN changes over the course of the afternoon yesterday?

I noticed at one point yesterday that 3-hour CIN trend was decreasing after the morning convection cleared and we started to heat (especially eastern PA / NJ / southeastern NY, but into CT and southeastern MA too)... things were looking good... then around 3pm CIN started to increase significantly across all of CT into southeast MA (as well as eastern PA, NJ, southeast NY). The line over PA/NY was still > 100 miles to the west of the CT border. Why the abrupt change for worse starting around 2-3pm, well before the line arrived?

Post any archived images if you have them...

[CT Rain]

The SPC mesoanalysis site can do more harm than good when taken verbatim. Weenies use caution when ripping and reading.

[CT Rain]

The SPC mesoanalysis site can do more harm than good when taken verbatim. Weenies use caution when ripping and reading.

Sorry this wasn't directed at wxniss - more directed at everyone including mets. There is certainly some value in websites like that but I think people get too wrapped up in the specific index and lose site of the overall setup. Visualizing how the atmosphere looks and varies in 3 dimensions and will interact with various storm scale processes is the key to forecasting convection. Throw in a bit of climo and you're in good shape.

I tell Wiz all the time to stop posting all these specific numbers and tell me how the setup will evolve. 4000 j/kg of SBCAPE and 3000 j/kg of MLCAPE and a sig tor paramater of xxxxxx all is great... but none of them are any use if you can't get convection to form in the first place lol.

[wxsniss]

Sorry this wasn't directed at wxniss - more directed at everyone including mets. There is certainly some value in websites like that but I think people get too wrapped up in the specific index and lose site of the overall setup. Visualizing how the atmosphere looks and varies in 3 dimensions and will interact with various storm scale processes is the key to forecasting convection. Throw in a bit of climo and you're in good shape.

I tell Wiz all the time to stop posting all these specific numbers and tell me how the setup will evolve. 4000 j/kg of SBCAPE and 3000 j/kg of MLCAPE and a sig tor paramater of xxxxxx all is great... but none of them are any use if you can't get convection to form in the first place lol.

Thanks Ryan. All good.

This isn't my profession or expertise, just an intense hobby. I can read all the textbooks I want, but that is far inadequate without the experience you and others share on this board. And a little healthy head-butting has always made this board better, keeping the weenies in check and the pros accountable.

[TalcottWx]

Sorry this wasn't directed at wxniss - more directed at everyone including mets. There is certainly some value in websites like that but I think people get too wrapped up in the specific index and lose site of the overall setup. Visualizing how the atmosphere looks and varies in 3 dimensions and will interact with various storm scale processes is the key to forecasting convection. Throw in a bit of climo and you're in good shape.

I tell Wiz all the time to stop posting all these specific numbers and tell me how the setup will evolve. 4000 j/kg of SBCAPE and 3000 j/kg of MLCAPE and a sig tor paramater of xxxxxx all is great... but none of them are any use if you can't get convection to form in the first place lol.

I have yet to see a widespread severe day without ML lapse being solid. Same with shear. Guess I value those two factors the most. You can have sky high instability numbers but it doesn't help without the other two.

I struggle significantly with understanding night time convection and forecasting it. Anyone care to describe the process along with how to predict it with a skew or model?

[OceanStWx]

I spent a good third of the day driving to Ithaca, but it did afford me the opportunity to drive across the respective boundaries in play.

There was a ton of convective debris for much of my ride in NY. In reality most places along 88 only had a couple hours of heating to work with. I suspect that farther east this was also the case, only peak heating had come and gone, so the potential surface heating was reduced. The deeper into NY I got, the more evident it was that there was going to be a significant differential heating boundary setting up near the border with PA. I'm not surprised this is where the LEWP structure was most pronounced, including tornadic circulations.

Overall, I'm not surprised that areas farther north and east were left out of the game. It's always dicey when we're relying on a warm front blasting north in a few hours in this part of the country. I feel much better when the air mass is already in place.

[free_man]

good thread.

couple very simple post-mortem thoughts/observations:

1. some of the hi-res models' simrad products were quite good with the evolution...fwiw...keeping this a S NYS/PA deal and not giving much of anything to SNE other than some showers. might be a foolish approach, but i always keep those products in the back of my mind. i think someone (Scooter?) may have made reference to the SPC WRF also not showing much. just a thought.

2. for our area (SNE), the air mass left a lot to be desired. 24 hours prior it was quite dry and in some areas further N and E actually a bit "cool". it was almost september-like in parts of MA with that stiff NNW wind and Tds near 10C. i know you can prime an environment relatively quickly, but we also know what happens locally when we advect high theta-e air into a departing canadian air mass. more often than not we end up on the losing side of that...or minimally you aren't going to be sitting on a powderkeg locally. so if you don't have the strong forcing, it's going to be tough.

3. speaking to the low-level warm tongue present between 900 and 800 mb...given our poor position relative to the best forcing, that, i assume, was the deciding factor in not getting any discrete activity fired off well in advance of the eventual LEWP. looking at some of the forecast soundings from Wed for spots that were expected to be more squarely warm-sectored like POU, SWF etc, it (the cap) was modeled to be present through ~21 or 22z. lots of CINH on there into late afternoon. had a couple of discrete cells been able to take advantage of the environment over NE PA and the southern hudson valley, the afternoon could have turned out quite differently. but we would have needed some ridiculous surface heating to make it happen given 24-26C temps aloft.

anyway...i don't think the day was a "bust" just that the SPC probs were too aggressive...too far NE.

Don't be so modest, that is not a "simple" breakdown. Only simple for verbage? Plenty of posts in this thread shed a lot of light.

The SPC WRF was really good for at least a couple runs around 03 or 06z?, showed the little bow echo/lewp forming across E PA and proceeding through NJ/NY - yet little else to the NE, where the atmosphere was worked over. That was "ftw"

[andyhb]

Great discussion here, we need more of this kind of stuff when events don't turn out as planned, not a bunch of people going off on each other regarding IMBY "busts" and whatnot.

Also, for those unfamiliar, Chumpson is Rich Thompson from the SPC.