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Aug 8th-10th Severe Wx

free_man

By free_man,
in New England

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CT Rain

CT Rain

Posted
Posted

The 18z GFS is quite interesting tomorrow...keeps helicity quite high and develops some modest instability.  Tomorrow is certainly a day to watch

 

Yeah I'm surprised the GFS is as robust as it is with the LLJ. Hodographs become very long and curved during the morning and that lingers into the early afternoon. With super low LCLs there is a definitely tornado threat - and if that holds - maybe a more substantial (i.e. not fakenado) threat. 

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weatherwiz

weatherwiz

Posted
Posted

Yeah I'm surprised the GFS is as robust as it is with the LLJ. Hodographs become very long and curved during the morning and that lingers into the early afternoon. With super low LCLs there is a definitely tornado threat - and if that holds - maybe a more substantial (i.e. not fakenado) threat. 

 

It also actually looks like CT (especially west of the River) would actually be the area of the best potential.  These areas will not only have the better chance to achieve some modest instability but the LLJ is modeled to be quite strong (even on the latest GFS) and there is a great deal of turning.  Even though lapse rates are weak, this is a situation where storms are going to be low topped so mid level lapse rates aren't overly important here, especially given how things are in the lowest 2-3km of the atmosphere.  

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nzucker

nzucker

Posted
Posted

It also actually looks like CT (especially west of the River) would actually be the area of the best potential. These areas will not only have the better chance to achieve some modest instability but the LLJ is modeled to be quite strong (even on the latest GFS) and there is a great deal of turning. Even though lapse rates are weak, this is a situation where storms are going to be low topped so mid level lapse rates aren't overly important here, especially given how things are in the lowest 2-3km of the atmosphere.

How about SE NY? Similar profiles here?
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Typhoon Tip

Typhoon Tip

Posted
Posted

Okay, I just analyzed the NAM-based soundings over ORH, BAF and ORE, for tomorrow.

 

It's pretty clear the NAM thinks there is a warm front cutting SW to NE through the area, between ~ White Plains NY to FIT and southern NH.  Helicoidal flow is deeper NW of that axis than it is over ORH, where it is much more shallow...possibly down to 1200' !   SE wind at the sfc at 18z, is shallowest over ORH.  

 

Helicity values are dangerous looking, exceeding some 430 m^2/S^2.   What's missing are very impressive EHI values, which as we know is an incorporation of CAPE into helicity, developed and is a better correlator for large scale severe outbreaks.  That said, as Ryan pointed out, L LCLs and terrain can assist things along.   

 

What I am interested in are these inconsistencies in where to place the heaviest rain axis.  The 06z NAM was farther NW, suggesting a more optimistic sky. The 12z was farther S, cutting debris cooled air into the helicity axis.  This 18z is about half way back NW again.  Point being, if there is ANY CAPE created in that axis, look the f out!   

 

Shortly after 22z, HPC analyzed a sfc cool front extended SW-NE through NYS.  Apparently the NAM is having a little trouble assessing where that feature lays down/comes to a halt tomorrow.   A wave of low pressure develops along, as already analyzed in SE IL, and this slips up along the boundary during the day tomorrow.  That would suggest the front at least bulges back NW as a warm front prior to the weak cyclone's arrival. Both the NAM and GFS show a small acceleration of a LLJ as this low traverses the area.  This could be a very nasty situation imo should more sun and better CAPE be generated.  If said cool boundary does not get as far S anticipated, then the area over all runs into a scenario where superb theta-e pooling takes place amid a column that features S/SE jet flowing into enough of a frontal slope to get parcels into LFC where winds veers WSW ... sufficient evacuation aloft.  

 

If we bank on extensive cloud capping with rain, then the threat would be substantially mitigated, because mechanics alone are marginal it would seem.  

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Typhoon Tip

Typhoon Tip

Posted
Posted

I am not sure what SPC tools are used to evaluate shear, but ...

 

 

...WV/VA...PA...MD/DE...NJ...SERN NY AND SRN NEW ENGLAND...
SWLY LOW LEVEL FLOW WILL BRING MOISTURE NEWD AS A WEAK LOW PRESSURE
TROUGH DEEPENS DURING THE DAY. MODEST DEEP LAYER MEAN WIND FIELDS
AND SHEAR AND MAY ALLOW FOR A FEW STORMS TO PRODUCE LOCALIZED STRONG
WIND GUSTS. HOWEVER...CLOUDS AND ONGOING PRECIP COULD HAMPER
DESTABILIZATION. 

 

...is a pretty clear understatement in my estimation.

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CT Rain

CT Rain

Posted
Posted

Okay, I just analyzed the NAM-based soundings over ORH, BAF and ORE, for tomorrow.

 

It's pretty clear the NAM thinks there is a warm front cutting SW to NE through the area, between ~ White Plains NY to FIT and southern NH.  Helicoidal flow is deeper NW of that axis than it is over ORH, where it is much more shallow...possibly down to 1200' !   SE wind at the sfc at 18z, is shallowest over ORH.  

 

Helicity values are dangerous looking, exceeding some 430 m^2/S^2.   What's missing are very impressive EHI values, which as we know is an incorporation of CAPE into helicity, developed and is a better correlator for large scale severe outbreaks.  That said, as Ryan pointed out, L LCLs and terrain can assist things along.   

 

What I am interested in are these inconsistencies in where to place the heaviest rain axis.  The 06z NAM was farther NW, suggesting a more optimistic sky. The 12z was farther S, cutting debris cooled air into the helicity axis.  This 18z is about half way back NW again.  Point being, if there is ANY CAPE created in that axis, look the f out!   

 

Shortly after 22z, HPC analyzed a sfc cool front extended SW-NE through NYS.  Apparently the NAM is having a little trouble assessing where that feature lays down/comes to a halt tomorrow.   A wave of low pressure develops along, as already analyzed in SE IL, and this slips up along the boundary during the day tomorrow.  That would suggest the front at least bulges back NW as a warm front prior to the weak cyclone's arrival. Both the NAM and GFS show a small acceleration of a LLJ as this low traverses the area.  This could be a very nasty situation imo should more sun and better CAPE be generated.  If said cool boundary does not get as far S anticipated, then the area over all runs into a scenario where superb theta-e pooling takes place amid a column that features S/SE jet flowing into enough of a frontal slope to get parcels into LFC where winds veers WSW ... sufficient evacuation aloft.  

 

If we bank on extensive cloud capping with rain, then the threat would be substantially mitigated, because mechanics alone are marginal it would seem.  

 

It seems to me the issue is whether or not a surface low develops/deepens along the front in eastern NY. The NAM has been insisting it will and now the GFS has jumped aboard. My guess is that at least some of this is convective feedback - but even weaker wind fields would lead to some impressive hodographs so we'll see. 

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CoastalWx

CoastalWx

Posted
Posted

Yeah - interesting that the GFS has it too (the NAM has had it all along). 

Yeah it's probably correct to some extent about the increased LLJ and feedback can be real...just not sure if we get the 50kts at 925mb like the 18z GFS has. In any case, looks rather interesting...esp if we can get some low level CAPE which seems possible.

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CT Rain

CT Rain

Posted
Posted

Yeah it's probably correct to some extent about the increased LLJ and feedback can be real...just not sure if we get the 50kts at 925mb like the 18z GFS has. In any case, looks rather interesting...esp if we can get some low level CAPE which seems possible.

 

The NAM has like 80 j/kg of 0-3km CAPE at 18z tomorrow at the same time as that hodograph I posted (>300 m2/s2 storm relative helicity). That's enough for sig tors lol. 

 

I posted some of my thoughts on my website... ryanhanrahan.com

 

As usual the typical caveats apply... but if the GFS or NAM have the right idea tomorrow will be interesting.

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Typhoon Tip

Typhoon Tip

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Posted

It seems to me the issue is whether or not a surface low develops/deepens along the front in eastern NY. The NAM has been insisting it will and now the GFS has jumped aboard. My guess is that at least some of this is convective feedback - but even weaker wind fields would lead to some impressive hodographs so we'll see. 

 

You know... couldn't agree more on the conv. fb -- it's definitely in this;  it's partial in why I am wondering if the sky is more optimistic and gee ... can't really insert ANY CAPE into that or there'd be hell to pay. 

 

I'm serious.  eyes popped when I saw helicity > 430 m2/s2 on the BUFKIT.    christ. 

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CoastalWx

CoastalWx

Posted
Posted

The NAM has like 80 j/kg of 0-3km CAPE at 18z tomorrow at the same time as that hodograph I posted (>300 m2/s2 storm relative helicity). That's enough for sig tors lol. 

 

I posted some of my thoughts on my website... ryanhanrahan.com

 

As usual the typical caveats apply... but if the GFS or NAM have the right idea tomorrow will be interesting.

 

The shear looks to be in place with low LCLs so we can probably count on that...even if we tone down the NAM...still good stuff. So I guess my question is can we squeeze some sun in. I think it may be tough to grab some breaks of sun, but marine influence should be minimal this time of year and the GFS pumps up dewpoints at 950mb...a level I like to look at. Perhaps the high dews make it just bouyant enough where we need minimal sun? We've seen that before.

 

I feel like these setups can really surprise, or become a complete dud if something as simple as removing 5-10kts of shear. 

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CT Rain

CT Rain

Posted
Posted

The shear looks to be in place with low LCLs so we can probably count on that...even if we tone down the NAM...still good stuff. So I guess my question is can we squeeze some sun in. I think it may be tough to grab some breaks of sun, but marine influence should be minimal this time of year and the GFS pumps up dewpoints at 950mb...a level I like to look at. Perhaps the high dews make it just bouyant enough where we need minimal sun? We've seen that before.

 

I feel like these setups can really surprise, or become a complete dud if something as simple as removing 5-10kts of shear. 

 

Yeah the time of year is huge too. July/August/early September makes a big difference when a strong SSE flow can actually help convection chances by bringing in some really high theta-e off the water and keeping LCLs/LFCs low. 

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CoastalWx

CoastalWx

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Posted

Yeah the time of year is huge too. July/August/early September makes a big difference when a strong SSE flow can actually help convection chances by bringing in some really high theta-e off the water and keeping LCLs/LFCs low. 

 

Yeah I wouldn't worry about the water this time of year. That water is already warmer than normal too. I'm really surprised at the shear progged...that caught my eye when I saw the GFS. This looks like a better setup than the one last month with Kevin's RFD. 

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Quincy

Quincy

Posted
Posted

Two things:

Not quite the same setup, but BDL spiked to 85 today. Imagine if we have any kind of breaks tomorrow.

I'll compare some forecast values to the last tornado day. I saved all of the analysis data. I have a feeling it will likely be a better setup, even if you tone down the NAM or side with GFS. Warmer SST's won't hurt either like some have said.

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CT Rain

CT Rain

Posted
Posted

I wish I could see the euro winds, but not at work unfortunately. From what I saw on free sites, it looks toned down from the NAM and GFS, but sufficient enough.

 

The Euro definitely seems to deepen that low with falling pressures across western New England/eastern New York as the front slides east. That should keep winds backed but not sure if the strong LLJ response on the GFS/NAM is overdone or not.

 

Obviously convective mode and amount of destabilization are still up in the air. 

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