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Possible late season severe outbreak morning of 10/8/14


CoastalWx

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Well with the shear, you can always get spin ups. I don't expect to see discrete stuff that much, but could be some. This isn't really something that would have cells that discrete IMO. It's a strong s/w moving through so it wouldn't surprise me to have a line with a few cells ahead of it.

 

I could certainly see a line with cells ahead of it.  Or perhaps even clusters of cells

Wiz - I'm not so sure the specifics about the orientation of the h5 jet streak matters all that much. Very strong synoptic forcing, enough instability, and very strong 0-1 and 0-3km shear are more important. The biggest discrimator between tornadic and non-tornadic tends to be that low level shear. 

 

I think it would only just further enhance lifting and give updrafts a bit more of a boost.  But yeah...low-level shear certainly isn't lacking in the case and for right now at least the models have what you would think is enough instability to work with.  

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My concerns for severe in eastern areas is that southerly flow normally has a stabilizing effect out this way.  Our best events are typically on a W/ NW flow.

 

Bob - this is one of the odd cases where the strongerly low level flow HELPS with severe potential. We're trying to advect 62F+ dew points into SNE and the warm SSTs south of us this time of year actually help with this. 

 

In spring and summer this is never a help... but there is a window in the fall where the warm water can actually help bring juicier CAPE inland. I think SE Mass looks the most impressive. 

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Bob - this is one of the odd cases where the strongerly low level flow HELPS with severe potential. We're trying to advect 62F+ dew points into SNE and the warm SSTs south of us this time of year actually help with this. 

 

In spring and summer this is never a help... but there is a window in the fall where the warm water can actually help bring juicier CAPE inland. I think SE Mass looks the most impressive. 

 

Agreed...right now I would favor SE MA...extending back into RI and SE CT

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Just looked up ACCAS. Eye in the sky.

 

Basically it's a sign that steeper mid level lapse rates are working into the area. Typically they will form just above the cap.

 

As the saying around the NWS goes, "ACCAS by 8, day shift stays late." When you have it early in the day, you know you have a cap in place and all day long to bake the ground beneath the cap. Think loaded gun.

 

In our case this morning, it's just a sign that we do have some decent lapse rates aloft to work with.

 

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Maybe one mitigating factor for tornadoes would be the storm motion. SPC WRF suggests storm motion around 200 degrees, so any cells would be crossing the warm front rather than paralleling it. Doesn't mean we can't spin up a quick one (a la Revere) though.

 

I wonder if the storm mode does go QLCS pretty quickly. Spinups in anything discrete early on and then embedded circulations in the QLCS? 

 

Given the amount of low level shear, low LCLs, and adequate CAPE it's not out of the question you could see a sig tor. 

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I wonder if the storm mode does go QLCS pretty quickly. Spinups in anything discrete early on and then embedded circulations in the QLCS? 

 

Given the amount of low level shear, low LCLs, and adequate CAPE it's not out of the question you could see a sig tor. 

 

ARW and NMM both show a QLCS between 09-12z.

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Almost all of the high resolution models at this point are hinting toward the development of organized convection over Eastern NJ. This makes sense when you look at the mid level jet orientation and the timing of the best forcing. The issue then becomes what develops in the prefrontal sector. The NAM has a noticeable cap on soundings essentially from LGA northeastward right ahead of the best forcing...and as Ryan and I were discussing the most favorable thetae orients itself from NYC eastward into Long Island and Southern New England.

 

I think discrete cells are likely initially and that's what is somewhat concerning to me given the kinematics in place. Overall setup argues for qlcs before too much time, but if anything discrete can ride the periphery of the best instability near the wf maximized low level shear, lookout. Wouldn't be surprised to see multiple spinups if all goes right and the NAM isn't out to lunch with its cap idea. 

 

PS- Only a brief window, but 6z NAM has 1000 j/kg of SBCAPE and 200-250 m2/s2 0-3km helicity over parts of Connecticut....in the morning on October 7th! Pretty cool to see.

 

5000627.gif

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Not sure why SLGT risk doesn't extend up to Boston. Oh well. 

 

Just had our morning briefing, my assessment is that model guidance is pointing towards the severe threat extending farther north than the SPC outlook area. Now some of that may be because BOS and points N are right around 12z tomorrow, which is when the SPC outlooks change from SWODY1 to SWODY2.

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Just had our morning briefing, my assessment is that model guidance is pointing towards the severe threat extending farther north than the SPC outlook area. Now some of that may be because BOS and points N are right around 12z tomorrow, which is when the SPC outlooks change from SWODY1 to SWODY2.

 

Yes - good point. 

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I'd like to see their wording or probabilities a bit more impressive before I go too nuts with the threat on air is that I was saying lol

 

They have the luxury of waiting this one out to see what happens today, or if the models trend any certain way with the cap or prefrontal convection. So I doubt we'll see them get aggressive until later on. 

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