***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
01-03z.
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.
