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Tuesday, October 24th, 2017 Strong to Severe Storm Potential


weatherwiz

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Intriguing setup for tomorrow which computer forecast models have been quite consistent on for the past week.  A rather potent upper-level trough which will continue to amplify as it progresses through the Ohio Valley will push a strong cold front eastward.  Very strong dynamics associated with this system, characterized by a 90+ knot 500mb MLJ streak in which we should end up in the RFQ.  With an anomalously warm and moist low-level airmass this should yield several hundred J of CAPE, even persisting well into the overnight hours.  The combination of modest CAPE, strong wind shear, and strong forcing will all contribute to perhaps multiple rounds of convection tomorrow with activity possible in the afternoon hours then again later in the evening.  The potential will exist for strong to damaging wind gusts in stronger convection.  Given the large hodographs as well we will have to watch for rotation.  It's also interesting how some of the hi-res guidance actually develops some discrete activity which usually doesn't happen much in these setups.

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Tue night and Wed...

Synoptic Overview...

Slow moving cold front becomes parallel to upper flow as mid
level trough takes on negative tilt. This front will be
associated with an impressive warm conveyor belt up the eastern
seaboard containing subtropical moisture with PWATs near the
2.00 inch mark, or nearly 3 std deviations above normal. Also
embedded within this warm conveyor belt is very strong wind
anomalies with 925 mb wind speeds of 55-65 kts, +4 std
deviations above climo! This low level jet builds a low level
thermal anomaly with nearly moist adiabatic lapse rates above
this warm anomaly. This very strong low level jet also advects
surface dew pts into the mid and upper 60s across southern New
England late Tue into early Wed, generating MUcapes of 300-500
j/kg, very impressive for late Oct.

Wind risk...

As mentioned above low level jet peaks at about 55-65 kt late
Tue into early Wed. Heavier showers (via precip drag) and
especially potential low top fine line (very strong frontal
convergence coupled with marginal instability) across western
MA/CT will increase the risk for stronger winds aloft mixing to
the surface. Given leaves remain on most trees, this will
exacerbate the risk for downed limbs or even some trees with
localized power outages. Wind headlines will likely be needed as
we draw closer to the event.

Heavy rain...

Subtropical moisture streams up the eastern seaboard with PWATs
nearing 2 inches, +4 std deviations from climo for about 24-30
hrs! This duration coupled with strong frontal forcing and
marginal instability should be sufficient for periods of heavy
showers with isolated thunder possible. Much of the global
guidance offering a widespread 1-2" rainfall amounts with
localized 3-5" possible especially eastern NY into western MA/CT
given greater risk of low top fine line.
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13 minutes ago, eekuasepinniW said:

 

"Rain. The rain could be heavy at times. High near 65. South wind 5 to 10 mph, with gusts as high as 20 mph. Chance of precipitation is 90%."

That wind sounds a little less damaging than I was expecting.

Tue night will see the closed low over the GReat Lakes to start
making a little better progress to the NE, but it will still be
a slow go. This will push the sfc front ewd into NH after
midnight. Ahead of the front, expecting a line of convection to
form as strong low level jet will be in place just ahead of the
front. With the deep moisture ahead of the front, this
convection will produce heavy rain, and the possibility of TSRA.
Any TSRA could also help mix down the winds from the jet, and
good see some gusts approaching severe levels. Currently, this
line should be somewhere in the vicinity of the NH/ME border
around daybreak on Wed, and will continue across ME Wed morning.
This line will likely be responsible for a large part of the
rain that falls and could produce an inch to inch and a half in
several hours.
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15 minutes ago, weatherwiz said:

I think people are sort of not understanding the wind situation.  This isn't a wind advisory type of setup where we have strong synoptic winds.  Winds will be gusty tomorrow but the main deal with the winds is whether convective elements mix down much stronger winds.  

Winds gust 35-50 mph synoptically. Anything above that comes with any convection 

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8 minutes ago, Damage In Tolland said:

Winds gust 35-50 mph synoptically. Anything above that comes with any convection 

If there were much steeper low-level lapse rates I could see it happening.  We’ll have gusts from the pressure gradient but nothing upwards of that magnitude.  

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31 minutes ago, Damage In Tolland said:

Ryan had 35-50 statewide with higher gusts in convection . This is an extremely volatile situation 

Euro remains underwhelming. 35 to 50 is probably right with a 60 gust in Branford and he will verify. Not exactly a huge deal,wind advisories in later fall are pretty climo.

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6 minutes ago, CT Rain said:

Looks pretty good to me. We have a bit of CAPE out there so convection could make things pretty interesting. 

bufkitprofile.png

holy crap.  

why isn't the WTBY sounding as impressive with those winds?  Really that much of a difference in wind potential between the two places.  

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Just now, weatherwiz said:

holy crap.  

why isn't the WTBY sounding as impressive with those winds?  Really that much of a difference in wind potential between the two places.  

You're probably talking a few tenths of a degree that is preventing the "mixing algorithm" from catching it. Given the neutral at worst look to boundary layer stability this event has a lot more potential than those inverted days with a 90 knot LLJ lol

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Just now, CT Rain said:

You're probably talking a few tenths of a degree that is preventing the "mixing algorithm" from catching it. Given the neutral at worst look to boundary layer stability this event has a lot more potential than those inverted days with a 90 knot LLJ lol

crap...that's my fault for only looking at a bufkit sounding for Waterbury.  I would have harped on the synoptic wind threat more.  

I completely agree...this event has a ton more potential than most setups we see of this nature.  Having no inversion (or any noticeable one) just above the deck makes this pretty eye opening.  Won't take a great deal of cape for things to happen.  Just a question of whether we get enough cape to really worry about rotation and meaningful rotation.  I'm sure everything will be rotating to some extent

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The LCL's tomorrow are going to be ridiculously low tomorrow...about as low as I think I've seen.  If we generate enough 0-3km CAPE that's going to make things extremely interesting.  With the degree of directional wind shear/speed shear in the lowest few km with those low LCL's...something will produce.

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