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2013 Mt. Holly CWA Convection Thread


SouthernNJ

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Pretty good size power outage in Franklin Twp. from that storm that moved through Williamstown, along with a few wires calls in Monroe Twp. I had just gotten back to the firehouse from a Disaster Drill at ACY, so I couldn't go after it, even though it was 5 miles away, lol.

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Here's one from earlier, down at our drill at ACY, when one of the many drenching storms moved in.ImageUploadedByTapatalk 21368314266.952783.jpg

Smoke.... Where was the drill at???? The old Bader Field, or the airport outside of town???

Actually at AC International in EHT. Simulated plane crash with 200 patients/victims. Was bad enough I got ridiculously drenched on the tarmac in full gear and a pack for 2 1/2 hours, I felt really bad for the 100 or so people playing victims, lol.

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See text for tomorrow for most of the area.

 

...UPPER OH VALLEY/DELMARVA...
  
   WEAK MID LEVEL HEIGHT FALLS WILL SPREAD ACROSS SERN CANADA/GREAT
   LAKES REGION INTO THE UPPER OH VALLEY LATE IN THE PERIOD.  WHILE
   ASSOCIATED SFC LOW/LARGE SCALE FORCING WILL SPREAD WELL NORTH OF THE
   CNTRL APPALACHIANS/DELMARVA...TRAILING FRONTAL ZONE WILL ADVANCE TO
   A POSITION FROM SYR TO PIT BY 16/00Z WITH N-S WARM FRONT EXPECTED TO
   ORIENT ITSELF ACROSS THE HUDSON VALLEY DURING THE LATE AFTERNOON.
   VEERED WLY FLOW WITHIN THE WARM SECTOR SHOULD ALLOW A BIT MORE
   MOISTURE TO ADVANCE ACROSS THE OH VALLEY INTO THIS REGION BUT REMAIN
   CONSIDERABLY DRIER THAN SEVERAL 12Z MODELS SUGGEST...LIKELY RISING
   ONLY INTO THE 50S.  AFTERNOON HEATING SHOULD CONTRIBUTE TO
   DESTABILIZATION ACROSS PA SUCH THAT ISOLATED THUNDERSTORMS COULD
   DEVELOP AHEAD OF THE COLD FRONT.  CONVECTION THAT EVOLVE ACROSS THIS
   REGION WOULD SPREAD SEWD TOWARD THE DELMARVA WITHIN STRONGLY SHEARED
   BUT WEAKLY UNSTABLE ENVIRONMENT.  FOR THIS REASON IT APPEARS 5
   PERCENT SEVERE PROBS FOR LOCALLY STRONG WINDS WILL SUFFICE ACROSS
   MUCH OF PA INTO THE DELMARVA.

post-89-0-78778400-1368554848_thumb.gif

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PS= Nam is probably overdone with instability. IF not, its something to keep an eye on tomorrow.

 

 

I've been on the road all day and so I haven't looked at anything yet, but those are same damn good parameters for our side of the Appalachians.  (You'd be surprised how many tornado days - regardless of area of the U.S. - are low CAPE/high shear days.)

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Earl Barker's model Skew-T page calculates a lot of indices for you:

 

 


150513NAMKPHL.png

But the site's GUI is god awful, so I've red-boxed some of the more useful parameters.  They're actually quite good for our area.  (0-3 km CAPE of 25.0 J/kg is probably more or less just "average," but whatever.)  Wind field would support eastward-propagating clusters/line segments (quickly though, ~35 kts) that would be probably be hail-producers.  There isn't *quite* enough turning for supercells, imo, but it's close.  

 

Two problems though: One is that it's the NAM, so all of those parameters (or at the very least, the thermodynamic ones) are likely overdone.  

 

Second is that there's no forcing.  It appears that there's a surface pressure trough down the East Coast not associated with any temp/moisture gradient, and some sort of frontal boundary stretching from the Low in Canada westward across OH, IN, and IL.  And of course there's the warm front, which the NAM has pushing through KPHL 21z-00z, along with the associated frontal inversion.  But within the warm sector itself, there's not much going on, which is why you see the NAM composite reflectivity showing a whole lotta nothing.  (The warm sector is actually not capped, or at least, not with an unbreakable cap.  The lack of convection really is just due to the lack of forcing, imo.)

 

Maybe there'll be one random storm that be a 3/22/1955 redux, haha.

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  • 3 weeks later...

Day 3 slight risk:

2y3ybavy.jpg

SPC AC 310756

DAY 3 CONVECTIVE OUTLOOK CORR 1

NWS STORM PREDICTION CENTER NORMAN OK

0256 AM CDT FRI MAY 31 2013

VALID 021200Z - 031200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE

NORTHEAST/MID-ATLANTIC STATES AND NEW ENGLAND...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS SOUTHWEST TX/SOUTHEAST

NM...

CORRECTED FOR GENERAL TSTM AREA

...NORTHEAST/MID-ATLANTIC STATES AND NEW ENGLAND...

A MID/HIGH LEVEL SPEED MAX IS EXPECTED TO SHIFT NORTHEASTWARD OVER

THE NORTHEAST STATES/NEW ENGLAND ON THE PERIPHERY OF AN UPPER TROUGH

PIVOTING OVER ONTARIO/QUEBEC AND THE GREAT LAKES REGION. WHILE

SHOWERS/SOME TSTMS MAY ACCOMPANY THE COLD FRONT EARLY

SUNDAY...POCKETS OF STRONGER DESTABILIZATION ARE PROBABLE AHEAD OF

THE FRONT...ALTHOUGH WEAK MID-LEVEL LAPSE RATES MAY TEMPER THE

OVERALL DEGREE OF DESTABILIZATION. EVEN SO...MLCAPE ON THE ORDER OF

1000 J/KG OR GREATER WILL BE SUFFICIENT FOR STRONG/SEVERE TSTM

DEVELOPMENT AND INTENSIFICATION INTO THE AFTERNOON.

AS STORMS MATURE...STRONG DEEP LAYER SOUTHWESTERLY

WINDS...ACCENTUATED BY AS MUCH AS 35-50 KT BETWEEN 2-6 KM...WILL

SUPPORT THE DEVELOPMENT OF ORGANIZED/SUSTAINED CLUSTERS OF STORMS

INCLUDING BOWS. DAMAGING WINDS WILL BE THE PRIMARY HAZARD...ALTHOUGH

SOME SEVERE HAIL/PERHAPS A TORNADO THREAT MAY EXIST AS WELL.

...

..GUYER.. 05/31/2013

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Something going against us is timing. The better forcing doest arrive till 0z-9z Sunday night Into Monday am. In sure there will be some chances with a lee side trough, but the timing with this screams "N&W" of the city for best chances of severe.

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Carnage for all of I-95 from NYC to WAS at 22z on tonight's SPC WRF:

 

6-2-13SPCWRF.gif

 

The NSSL WRF, not shown, is significantly less impressive, but it also has the idea of multiple lines tomorrow evening (although most are broken/scattered, and on this particular run Philly and immediate burbs miss out).

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15% for Wind and Hail was pulled all the way to the coast, but the 30% Wind was cut off north of NYC with the 1630.  Discussion didn't specifically mention why the 30% was pulled back, but it seems that more cloud cover down here limiting instability was what prompted them to do it.

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