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wdrag

Potential few SVR/FF events parts of NYC forum Wed-Thu 7/22-23/20

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After yesterdays long range failure of convection (arrived Sunday night), must look ahead.

Modeling, SPC, WPC graphics all suggest opportunity for heavy convection Wednesday-Thursday (22-23). Attached the 6 hr County Average threshold FFG, with hourly guidance even lower amounts. This shows vulnerability in parts of ne NJ and se NYS, plus urban paved environments. SPC Days 1-3 is attached as issued early Tuesday. Also, added a brief 06z/21 GFS snapshot of modeled winds aloft for LGA via Bob Hart's web page (time is in UTC). Note the near 30 kt or greater westerly flow at 500 and 300 MB, showing the idea of enough wind to foster development of SVR organization and strong downdrafts.  In these two days, "isolated" storm totals of 4" easily possible with 'general' two-day total amounts of 1/2-2".  

Warm Air Advection (WAA)  instability burst (KI popping into the upper 30s from southwest to northeast by daybreak Wednesday driven by a modeled small 850MB 30 kt jet core in central PA overnight) 'should' develop some briefly heavy showers or a thunderstorm for parts of our NYC forum early Wednesday morning, especially nw NJ/se NYS. 

After any clusters pass, cloud debris/instability pooling and surface wind shift convergence boundaries will probably be the determinants of when and where heavy convection occurs Wednesday afternoon through Thursday evening. Heaviest should be afternoon-early evening and per modeling, think the bulk of the FF/SVR should be along and north of I80 (far northern NJ, se NYS, CT and LI) but I defer to your assessments, and those of the NWS offices/SPC/WPC, and the modeling from the HRRR and SPC HREF. 734A/21 

Screen_Shot_2020-07-21_at_5_37.48_AM.png

Screen Shot 2020-07-21 at 6.55.50 AM.png

Screen_Shot_2020-07-21_at_7_10.37_AM.png

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Biggest convection both Wednesday and Thursday should be afternoon or evening, depending on where you are.  And so... probably okay for a 90 min drive Thursday, but subject to an update Wednesday or even Thursday before 6A.  Not sure if anyone noticed, but SPC 13z D1 marginal update has been bulged northward slightly in PA.  Thinking that might reflect fairly robust nighttime WAA out there.  We'll see how it goes. 

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Euro looking very dry for tomorrow. Has most of the activity for Thursday. Not that I expect a global model to nail this type of set up 

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30 minutes ago, wdrag said:

Fortunately the EC is not known for its convective prowess.  However, am a little concerned that Thursday especially may not produce much if the wind at 850 shifts to west or northwest too soon on Thursday.  Need to reevaluate Wednesday morning.  One day at a time. 

I see 18z RGEM has a really nice line of storms for tomorrow.  Models like RGEM and HRRR really picking up on the convection for tomorrow that the EC would miss, as you said. Looks like a nice severe weather day tomorrow.

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We are off to a good start tonight with the downpours moving through this area.  Have picked up 0.52” with ponding on the roadways.

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Good Wednesday morning everyone, Add graphics etc as you like. After reevaluation using guidance through 09z/22, made no change regarding the topic discussion.

I'll add two incomplete graphics for the overnight event which is ongoing (eastward and soon ending) the extreme east portion of our NYC forum (LI,CT). Lightning accumulation graphic was snapped around 514A, and the Radar storm total will continue adding on for LI/CT through 830AM. 

Today: Modeling is trying to focus a line through virtually all of our area 5-9P, but there could be isolated storms ahead of it this afternoon, and maybe another cluster or two trailing behind the primary line  - up till about midnight, especially se NYS and nw NJ.

Thursday: wind fields look a little stronger to me for an even better chance of SVR/FF late in the day or evening.  Monitor SPC guidance for any upgrade in their thinking. 

FOG may be a problem the next two afternoons along the south coast of LI, especially Suffolk County. Otherwise heat wave should continue non marine influenced coastal plain next two days. 

Had .07 on the northern fringe of the southern overnight complex (~1235A). Saw one quarter inch near Patterson, NJ. 614A/22

Screen Shot 2020-07-22 at 5.16.37 AM.png

Screen Shot 2020-07-22 at 5.59.00 AM.png

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16 minutes ago, Stormlover74 said:

Watch issued to our south and west. Hope all that activity doesn't rob us up here

Models for our area aren't as impressive as they looked yesterday. HRRR isn't showing much activity. Looks as if the storms for our area today will be very isolated. At least we have another chance tomorrow if today doesn't deliver.

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Quickly reevaluated with latest guidance (RGEM, GFS, NAM, NAM3K HRRR and last nights ARW 1 and 2).  Please point out what I'm missing.  I could be missing something.  

Otherwise,

I'm seeing poor 12z model radar init for 16z. and wherever I see it has something, the development is northeast toward virtually all of our NYC forum by late afternoon.  16z S wind IPT area with dew points in the 70s in e PA/NJ/NY, plus cu fields from ne PA into nw NJ suggest to me to look for further developement northeastward in this cu field and eventual big storms by 5P.   I could be wrong... so no guarantee but that's what I see from a quick glance at surface, cu fields and modeling.   Big storm suggestion is the anvil blowoff in the little cell vicinity York PA past 45 min. 

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Also, fwiw... the primary line had previously been slated by primary USA guidance in the 5-9P slot for our area.  Am not too worried, yet.  New cell near ABE and it looks to me like central PA activity is developing enewd.  I may be off line for a couple of hours. Ride it out a little while longer and follow NWS/SPC discussions and your own observations of surface convergence, and cu field pooling-development. Thanks. 

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SPC at 145PM EDT.  No guarantee for for me in Wantage we may miss the first batch developing east northeast from vcnty Brodheadsville in ne PA. storm looks impressive at 153P. This should be the batch to watch. again, no guarantees. Hope this works out well.

https://www.spc.noaa.gov/products/md/md1313.html

Mesoscale Discussion 1313
   NWS Storm Prediction Center Norman OK
   1245 PM CDT Wed Jul 22 2020

   Areas affected...portions of eastern PA...NJ...southern NY and
   southern New England

   Concerning...Severe potential...Watch possible 

   Valid 221745Z - 221945Z

   Probability of Watch Issuance...60 percent

   SUMMARY...Scattered thunderstorms will increase in coverage and
   intensity through the afternoon. Strong, locally damaging gusts will
   be possible with these storms into this evening.

   DISCUSSION...A broad area of deepening cumulus continues to develop
   across portions of eastern PA/NJ northeastward into southern New
   England ahead of a shortwave vorticity max. At the surface, a warm
   front extends from central NY east/southeast into CT/RI. South of
   the front, surface dewpoints are mainly in the 70s F and strong
   heating has allowed temperatures to warm into the mid to upper 80s
   F. As a result, a tongue of MLCAPE from 500-1500 J/kg resides from
   eastern PA and NJ northward into southern NY and western CT. The
   warm front should progress northward a bit more through the
   afternoon and at least weak destabilization is expected as far north
   as southern VT/NH into western/central MA. 

   In addition to weak to moderate instability, moderate deep shear
   resides over the region, and effective bulk shear around 35-45 kt
   should overspread the entire MCD area by late afternoon. Some
   uncertainty with regards to convection initiation remains, largely
   due to weak forcing across the area. A vorticity max further east
   near Lakes Erie/Ontario should spread eastward with time, but
   initial convective development may be largely driven by diurnal
   processes, especially over southern portions of the MCD area from
   far southern NY/Long Island southward into NJ. Nevertheless, the
   overall environment should support organized cells and clusters,
   once they develop. Midlevel lapse rates will remain modest, but
   strong heating has resulted in steep low level lapse rates south of
   the warm front, and PW values greater than 1.75 inches will further
   aid in strong downburst potential. 

   While timing of convection remains a bit uncertainty, at least
   sporadic instances of severe gusts and locally damaging winds are
   expected into the evening hours, and a watch may be needed this
   afternoon, within the next few hours.

   ..Leitman/Hart.. 07/22/2020

 

 

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VIL on the ne PA cell only briefly mid 40s thru 2P while the one near York Pa looked briefly like a 70vil (SVR, I think hail for sure somewhere in that one).  The ne PA storm might have suprising injury causing lightning the way its spread "behind" the primary cells and it looks like G winds near 35 kt with hail from what I can tell.  Bottom line, storms are organizing for the SPC MCD area.  Probably off line til 4ish. 

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Chance at a few supercells with discrete activity ahead of the main line.

One such SVR warned cell moving through Sussex County now.

The main line is centered over Central/Eastern PA and most intense area is currently focused on the DC area with developing MCS feature.

Further development should continue and multiple rounds of convection are possible from late this afternoon into the first part of the night.

Latest HRRR soundings indicate only about 1500-1800 J/KG of SBCAPE around 23-00z which looks severely underdone based on current observations below.

sbcp.gif?1595445459692

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Just an observation... the cell missing most of southern Wantage NJ with just TRW- so far, is rolling thunder. Not the cracks that startle. CB top sort of look capped, lots of light coming in from the south through the rain, and the cu ahead of it are frayed.  Hope a line develops behind this Sussex County NJ loner.  Just doesn't seem like everything is ready to erupt up here. May be it will go further east, or develop toward 5 or 6P.  Noticed no reports yet to the NWS.  

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23 minutes ago, wdrag said:

Just an observation... the cell missing most of southern Wantage NJ with just TRW- so far, is rolling thunder. Not the cracks that startle. CB top sort of look capped, lots of light coming in from the south through the rain, and the cu ahead of it are frayed.  Hope a line develops behind this Sussex County NJ loner.  Just doesn't seem like everything is ready to erupt up here. May be it will go further east, or develop toward 5 or 6P.  Noticed no reports yet to the NWS.  

I love your play by play analysis during these convective episodes.  Very informative and valuable your expert take, thank you! 

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9 minutes ago, wdrag said:

Just an observation... the cell missing most of southern Wantage NJ with just TRW- so far, is rolling thunder. Not the cracks that startle. CB top sort of look capped, lots of light coming in from the south through the rain, and the cu ahead of it are frayed.  Hope a line develops behind this Sussex County NJ loner.  Just doesn't seem like everything is ready to erupt up here. May be it will go further east, or develop toward 5 or 6P.  Noticed no reports yet to the NWS.  

That cell is right on the edge of the stronger shear. Most of that is located further North and East over Upstate NY and Western New England.

Thinking that we need to wait for the line in PA for anything significant. 

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21 minutes ago, White Gorilla said:

I love your play by play analysis during these convective episodes.  Very informative and valuable your expert take, thank you! 

Thanks...  see others as well. NJwx85 just commented.  By the way, 2 reports of damage now in the Pike County storm.  Think I'll leave this play out through 9P and see what happens. I see other warnings by PHI now so...slowly growing.  Walt  357P/22

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