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  • Writer's pictureMy Personal Weatherman™

***Latest info on the strong to severe thunderstorms for this evening***

- The 1st and 2nd images show the future radar for 8 PM and 9 PM, and the 3rd and 4th images are from NWS NY and NWS Boston. Heavy downpours, frequent lightning, hail, damaging wind gusts up to 60 mph, and even a tornado are all in play.

- Here is a very interesting discussion from NWS NY covering Long Island and the tri-state area:

Attention then turns to the aforementioned upper low/trough
and the associated cold front poised to sweep across the region
this evening. Along and just ahead of the front and upper low 
will be a strongly forced low-topped line of convection. This 
convection will be working its way across upstate NY and PA in 
the afternoon and then should be nearing the Lower Hudson Valley
21-23z, and over the NYC metro/Hudson River Corridor 23-01z. 
The line then encounters the stronger maritime influence and 
should weaken as it moves across central/eastern LI and CT 

As is usually the case in our area with convection, the amount
of instability is still uncertain. Some of the CAMs indicate 
500-1000 J/kg of MLCAPE that develops in the afternoon from the 
NYC metro on N and W. Other CAMs indicate lower CAPE values. 
Confidence is much higher in there being a tremendous amount of 
unidirectional shear. These low CAPE high shear environments can
cause convection to struggle to organize to severe levels. The 
strong forcing from the upper low in this case may help with 
updraft organization moreso than what we see later in the warm 
season in similar low CAPE high shear environments. While there 
may be some instability further east in the maritime influence, 
it may be elevated so the concern for severe weather is lower 
here. SPC has continued to place most of the area in a slight 
risk for severe weather. The primary threat is damaging wind 
gusts in excess of 58 mph hour. Large hail is also a threat, 
mainly west of the NYC metro as the higher CAPE may couple with 
the colder air aloft from the upper low. These threats are more 
limited east of the NYC metro and SW CT in the maritime 
environment. However, small hail cannot be ruled out anywhere 
given the cold pocket aloft. 

Another concern that will need to be watched is some CAMs continue 
to back the low level flow immediately ahead of the front, 
increasing helicity. There is a 5 percent chance of a tornadic 
development in NE NJ with a 2 percent risk in the Lower Hudson 
Valley and NYC metro and SW CT. 

As noted in the previous discussion, there are lots of conditional 
probabilities with this event. Should the ingredients all line up, a 
squall line with some discrete rotating cells is a possibility.

As for non-thunderstorm winds, pre and post-frontal gusts could 
reach 35-40 mph, especially away from the coast this afternoon
ahead of the front. Think gusts will be held down a but further
east due to a stronger inversion. Mixing looks much stronger 
behind the cold front passage Saturday evening and night. Gusts 
immediately behind the front could reach 40-45 mph, with some 
isolated gusts to 50 mph. The chance of this is brief and if it 
were to occur would be immediately behind the front, with gusts 
remaining 30-40 mph for the rest of the night. No wind advisory 
has been issued at this time. 

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