Northeast Severe/Convective/Thunder thread II

[CT Rain]

Areas to western MA through SW NH and into NW CT are in for a good show I think. Maybe we can bring that into ORH-TOL?

You didn't hear... Tolland is now considered western New England?

[moneypitmike]

19Z RAP increases EHI over western Mass in the next 4 hours

anyone have thoughts on potential for western half of Mass early evening?

cell in southeast NY / north of Monitcello not doing much yet

What is EHI?

[CoastalWx]

You didn't hear... Tolland is now considered western New England?

That's right. Well, he does take the temp from Norfolk in the winter so........

[Typhoon Tip]

lol I don't think so

There's a wind shift that moved through with the sea breeze front but HFD is still 31/22. We're fine.

Cu development abated abruptly when the wind shift came through. That's stability.

I've seen this many times growing up in this part of the country with these S arriving stablizers. It doesn't reflect on the thermometer very well. Otherwise you wouldn't have lost your Cu.

But ... large scale ascent would overcome that if it can arrive from the W.

[SquatchinNY]

What is EHI?

Energy Helicity Index. If I remember correctly, CapexHelicity/12000?

[TalcottWx]

What is EHI?

Just another supercell parameter really

[CoastalWx]

Aside from those more discrete cells in SW NH, this will be primarily a wind event as the squall line develops and moves east.

[CoastalWx]

What is EHI?

The basic premise behind the EHI (Energy-Helicity Index) is that storm rotation should be maximized when CAPE is large and SRH is large. 0-1-km EHI values greater than 1-2 have been associated with significant tornadoes in supercells.

[Allenson]

I have close relatives in Bradford and Corinth VT... Sure wish I was up there now.

Actually hasn't been too bad here so far. Last night was a lot worse.

Cool murky air here as taken the severe punch out of things.

I wonder if I know your relatives?

[moneypitmike]

Energy Helicity Index. If I remember correctly, CapexHelicity/12000?

Thanks--now I'll just have to figure out how to interpret it.

Moving into overcast again, though no thunder like the last time this happened (I think that was from the SVTcell that skirted by at about 2:00p.m.).

84.1/72

[CoastalWx]

Tomorrow looks interesting as well...even for ern areas.

[moneypitmike]

Nice cool-down where the rains have gone through.

[Typhoon Tip]

3500 SB CAPE. 3k+ MU Cape. Li -9. Sounds unstable no?

You have to understand something... Atmosphere thermodynamics has rather discrete tolerances. A fraction of a degree can prevent activation.

It doesn't matter if CAPE is high. If the trigger point were say, 32C, and it's 31.5C, and there is no other forcing present at that time, you can say it is hot and humid with bloated CAPE until your blue in the face, it ain't going to make it happen!

When the wind shifted S it transported some stablizing influence, otherwise your Cu field would still be activated. That's not really open to debate.

[wxsniss]

Thanks TT

What is EHI?

EHI = energy helicity index = (CAPE x H) / 160,000

tool for factoring in both instability and helicity to produce rotating supercells

not in itself sufficient or complete to predict tornadoes, but 0-3 km EHI > 2 or 3 or 1-2km EHI > 1 or 2 at least is thought a necessary parameter for tornadogenesis

i'm far from an expert... here's more reading:

http://www.spc.noaa....p/help_ehi.html

http://www.stormtrac...orecast/ehi.htm

[CoastalWx]

Mike, treat it as a combo that combined CAPE and helicity. Helicity is a measure of rotation, so you want those two to really hook up.

[weatherwiz]

Friend of mine in VT had bigger than golf ball hail.

We are still in Troy...just NE.

We are going to eventually go about 5 miles more NE up RT 7 from where we are at...google Earth shows some great spots with awesome views.

Also, sfc winds REALLY picking up here...from south to southwest.

[Tropopause_Fold]

nice outflow boundary racing toward Wiz

[moneypitmike]

Scorching and humid, can just feel the moisture convecting out of the ground.

Cumulonimbus towering all around the valley, gonna' take a ride with the baby and snap some photos. Looks like we don't get in on the action until evening.

Don't say that too quickly, Chris. Just had a couple rumbles (thought the sun's back out)..

83.8/72

[OceanStWx]

The storms that are getting the tornado warnings are really maximizing helicity on the low level boundaries. In NY they are feeding off the old OFB, which is extending eastward into central VT where the latest TOR went out. In southwestern NH they are using the warm front to spin up as the cross the boundary.

[heavy_wx]

Also a nice outflow boundary in Delaware county initiating a storm.

[TalcottWx]

You have to understand something... Atmosphere thermodynamics has rather discrete tolerances. A fraction of a degree can prevent activation.

It doesn't matter if CAPE is high. If the trigger point were say, 32C, and it's 31.5C, and there is no other forcing present at that time, you can say it is hot and humid with bloated CAPE until your blue in the face, it ain't going to make it happen!

When the wind shifted S it transported some stablizing influence, otherwise your Cu field would still be activated. That's not really open to debate.

I really doubt this 'stabilizing influence' will have any more than a minuscule impact on the line that will and has always been progged to move through hours from now. The damage has already been done and the instability is still in the atmosphere. This isn't a fog bank dropping Logan down 30F in an hour in July.

[CT Rain]

Cu development abated abruptly when the wind shift came through. That's stability.

I've seen this many times growing up in this part of the country with these S arriving stablizers. It doesn't reflect on the thermometer very well. Otherwise you wouldn't have lost your Cu.

But ... large scale ascent would overcome that if it can arrive from the W.

Yes we have a very minor amount of CIN. we've gone from 33-32C. Whenever there is a burp in the atmosphere (outflow boundary, etc) we'll overcome that CIN. It's not really an issue most of our big svr days in CT start with a cu field, go to no cu, and then the real stuff moves in.

[weatherwiz]

Alright...making a qucik trip to the gas station then off to this field about 5-10 miles up the road. I'll be posting again when I get home tonight.

[Damage In Tolland]

You didn't hear... Tolland is now considered western New England?

And HFD is? LOL

[Typhoon Tip]

Flood may become a concern in that southern NH stuff as it is beginning to train up over the lift caused by this BD boundary

[weatherwiz]

Actually perhaps thinking of staying right here at the McDonalds...?

[TalcottWx]

Alright...making a qucik trip to the gas station then off to this field about 5-10 miles up the road. I'll be posting again when I get home tonight.

I was going to say you should do exactly that. Nasty looking stuff up there

[Typhoon Tip]

Yes we have a very minor amount of CIN. we've gone from 33-32C. Whenever there is a burp in the atmosphere (outflow boundary, etc) we'll overcome that CIN. It's not really an issue most of our big svr days in CT start with a cu field, go to no cu, and then the real stuff moves in.

It'll be interesting to track... The stuff in NYS appears to be weakening slightly. How smoked is central NE over the last 12 hours though!

wow

[CT Rain]

And HFD is? LOL

Yeah lol

It was just comical because it the winter you claim to be in central NE.

Anyways an interesting threat. Some isolated stuff starting to pop up in the Hudson Valley. May be a threat to Litchfield County.

[moneypitmike]

Mike, treat it as a combo that combined CAPE and helicity. Helicity is a measure of rotation, so you want those two to really hook up.

Thanks, Scott.

Do you expect we'll have watches put up in the BOX zones at some point? Nice to see things beginning to pop right on I-87. Those could have the potential to work their way into the BOX CWA--at least the western zones.