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2013 Mt. Holly CWA Convection Thread


SouthernNJ

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Parents had 2.30" in the CoCoRaHS gauge as of about 10 minutes ago.

 

Here's a picture of my brother's back yard.  He's only lived there about a year but he hasn't seen it flood like this before.  There is no stream back there, btw.

post-39-0-84161400-1372380687_thumb.jpg

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Yet another impressive rain event here in NW Chesco here in June - another 1.15" today which puts us at 10.89" for the month...this now represents the 3rd highest June rain total since 1894. With the pattern...there is certainly a shot to get to the wettest June in recorded history.

 

1938 - 12.18"

2003 - 11.37"

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Pick up .31" yesterday for a total of .71" for the week.

Also day 5 of Slight risk I believe with:

 

30% Wind if your on the PA/MD Border basically 15% for the rest, 15% hail and 2% tornado.

day1otlk_1200.gif

...ERN PORTIONS OF OH VALLEY...MID ATLANTIC THROUGH NERN STATES...   WSWLY WINDS ALOFT WILL STRENGTHEN AS A RESULT OF THE AMPLIFYING   UPPER TROUGH. UPPER 60S TO NEAR 70 DEWPOINTS WILL EXIST EAST OF LEE   TROUGH SUPPORTING MODERATE /1000-2000 J/KG/ MLCAPE AS THE SFC LAYER   WARMS DURING THE AFTERNOON. STORMS WILL ONCE AGAIN DEVELOP BY LATE   MORNING INTO THE AFTERNOON OVER THE HIGHER TERRAIN AND IN LOW-LEVEL   CONVERGENCE ZONE AND SPREAD INTO THE DESTABILIZING WARM SECTOR.   OTHER STORMS WILL INITIATE WITHIN THE WEAKLY CAPPED ENVIRONMENT OVER   THE OH VALLEY. VERTICAL SHEAR INCREASING TO 30-40 KT WILL SUPPORT   POSSIBILITY OF ORGANIZED STORMS INCLUDING  POTENTIAL FOR BOWING LINE   SEGMENTS AND UPDRAFT ROTATION. ISOLATED DAMAGING WIND AND LARGE HAIL   WILL BE THE MAIN THREATS INTO EARLY EVENING. 
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9AM update keeps same probabilities from the earlier forecast 30% 15% 2%

 

...ERN OH VLY TO CAROLINAS/MID-ATLANTIC/NORTHEAST THIS AFTN/EVE...
   DEEP...MODERATE W TO WSW MID-LVL FLOW WILL PREVAIL OVER MUCH OF THE
   EAST TODAY...ON DOWNSTREAM SIDE OF AMPLIFYING UPR TROUGH. SFC
   DEWPOINTS WILL REMAIN IN THE 60S TO NEAR 70 F...ESPECIALLY ALONG LEE
   TROUGH. SATELLITE SUGGESTS THAT SFC HEATING WILL BE STRONG IN MOST
   AREAS. GIVEN RELATIVELY COOL MID-LVL TEMPS AND ABSENCE OF
   APPRECIABLE CIN...SETUP SHOULD YIELD FAIRLY WIDESPREAD COVERAGE OF
   DIURNALLY-ENHANCED STORMS...ESPECIALLY BY EARLY AFTN FROM VA/WV NEWD
   INTO ERN PA/NJ/SE NY/CT...AND A BIT LATER IN THE DAY OVER THE
   WRN/CNTRL CAROLINAS.

   STORMS INITIALLY MAY FOCUS DOWNSTREAM FROM UPR DISTURBANCES NOW
   MOVING TOWARD OH/PA/WV...AND A BIT OVER THE SRN APPALACHIANS AND LEE
   TROUGH. 30-40 KT W TO WSWLY DEEP SHEAR SHOULD PROMOTE STORM
   SUSTENANCE/ORGANIZATION. ASSOCIATED LINES...BOWING SEGMENTS...AND
   ROTATING MID-LVL CORES COULD POSE A RISK FOR DMGG WIND GUSTS AND SVR
   HAIL THROUGH EARLY TNGT.

 

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Philly and DC in a tornado watch?  With only 25 knots of effective shear?  I guess werider things have happened. I think the 2500-3000 CAPE will help to intensify the storms this afternoon. Perhaps the SPC is being extra careful.

 

In their defense, the situation was contingent on a gradual increase in effective shear which was noted on the VAD wind ~ 7-8pm (it was always modeled to come just a little too late). They also made sure to keep the wording as "tornado or two" or "isolated" given the lack of speed shear. Perhaps it could have been centered more N/W but overall it wasn't a terrible decision (esp. with what happened to the west of the big cities).

For a while there, I think we all held our breath as 2 lines of low-topped convection (with occasional bursts >40KFT) moved through the region with mild attempts at organizing mesos. I saw a few interesting cloud formations with the first cell that went from Burlington to Mercer. I won't say it was rotating, rotating, but it certainly was close with clear striations, convergence near the inflow notch/appendage. It was close...

 

Hmm, am actually surprised about the tornado watch. I would have thought a severe thunderstorm watch instead. I see the rotation overall as the MCV lifts northeast, but figured the main threat would be locally damaging straight line winds.

Yeah I can see either point but I would say it was almost there yesterday between 5-7pm (transient structures/weak attempts at mesos). They did make sure to mention the winds were the main threat, as they usually are in any event but I do understand public perception issues when "tornado watch" is issued over "severe."

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So we might get an MD soon and maybe a watch later? Or does the timing play out bad for us in our region?

 

 

 

mcd1285.gif
   MESOSCALE DISCUSSION 1285   NWS STORM PREDICTION CENTER NORMAN OK   1202 PM CDT FRI JUN 28 2013   AREAS AFFECTED...PORTIONS OH...PA...MD...SERN LOWER   MI...DC...WV...NRN VA...EXTREME SRN PORTIONS WRN NY.   CONCERNING...SEVERE POTENTIAL...WATCH LIKELY    VALID 281702Z - 281900Z   PROBABILITY OF WATCH ISSUANCE...95 PERCENT   SUMMARY...WW IS REQUIRED FOR PORTIONS SRN PA...MD...NRN VA AND   WV...AND ANOTHER WW IS POSSIBLE ELSEWHERE ACROSS BROADER DISCUSSION   AREA AS TRENDS INDICATE.   DISCUSSION...BROAD AREA OF TSTMS HAS BEEN GRADUALLY BUILDING FROM   SERN LOWER MI EWD ACROSS UPPER OH VALLEY REGION AND INTO N-CENTRAL   APPALACHIANS.  INITIALLY WIDELY SCATTERED COVERAGE SHOULD BECOME   MORE DENSE...AND CONVECTION MORE INTENSE...WHILE MOVING INTO   INCREASINGLY UNSTABLE BOUNDARY LAYER.  MAIN CONCERN IS DAMAGING   WIND...WITH OCNL HAIL ALSO POSSIBLE.   CONVECTION HAS FORMED IN DECREASINGLY CAPPED AIR MASS...ON BOTH   SIDES OF ILL-DEFINED FRONTAL ZONE EXTENDING SWWD FROM SFC LOW OVER   UPPER HUDSON RIVER REGION.  SFC DEW POINTS GENERALLY 60S F...BUT   INCREASING TO NEAR 70 AROUND CHESAPEAKE BAY AND DE VALLEY   REGIONS...COMBINE WITH SFC DIABATIC HEATING OF PRECONVECTIVE AIR   MASS TO YIELD 1000-1500 J/KG MLCAPE IN MODIFIED RAOBS AND FCST   SOUNDINGS.  KINEMATIC PROFILES ARE MOSTLY WLY AND NEARLY   UNIDIRECTIONAL...INDICATING PREDOMINANT QUASI-LINEAR EVOLUTION WITH   DAMAGING GUSTS BEING GREATEST CONCERN.  DEEP SHEAR INCREASES WITH   SWD EXTENT FROM UPPER GREAT LAKES INTO PORTIONS WV AND NRN VA...WITH   EFFECTIVE SHEAR MAGNITUDES PEAKING AROUND 50 KT OVER LATTER AREAS.    MOST PROBABLE AREA FOR UPSCALE ORGANIZATION/GROWTH APPEARS TO BE ON   NRN FRINGES OF STRONGER SHEAR BELT...WHERE TSTMS HAVE COALESCED   ACROSS PORTIONS SERN OH...NRN WV PANHANDLE AND SWRN PA.  ANY SUCH   EVOLUTION WOULD DRIVE FORWARD-PROPAGATING MCS EWD TO ESEWD ASTRIDE   PA/MD BORDER REGION...EVENTUALLY WITH POTENTIAL TO AFFECT CHESAPEAKE   BAY/DE RIVER REGIONS.
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SEL7

URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 387

NWS STORM PREDICTION CENTER NORMAN OK

210 PM EDT FRI JUN 28 2013

THE NWS STORM PREDICTION CENTER HAS ISSUED A

* SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

DISTRICT OF COLUMBIA

DELAWARE

CENTRAL AND EASTERN MARYLAND

CENTRAL AND SOUTHERN NEW JERSEY

SOUTHEAST PENNSYLVANIA

NORTHEAST VIRGINIA

COASTAL WATERS

* EFFECTIVE THIS FRIDAY AFTERNOON AND EVENING FROM 210 PM UNTIL

900 PM EDT.

* PRIMARY THREATS INCLUDE...

SEVERAL DAMAGING WIND GUSTS TO 70 MPH POSSIBLE

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 75

STATUTE MILES EAST AND WEST OF A LINE FROM 40 MILES SOUTH

SOUTHEAST OF WASHINGTON DISTRICT OF COLUM TO 15 MILES NORTH OF

TRENTON NEW JERSEY. FOR A COMPLETE DEPICTION OF THE WATCH SEE

THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU7).

PRECAUTIONARY/PREPAREDNESS ACTIONS...

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE

FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH

AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR

THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS

AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY

DO PRODUCE TORNADOES.

&&

OTHER WATCH INFORMATION...CONTINUE...WW 385...WW 386...

DISCUSSION...A FURTHER INCREASE IN TSTM COVERAGE IS ANTICIPATED THIS

AFTERNOON ALONG A DEVELOPING LEE TROUGH WERE THE ENVIRONMENT HAS

BECOME UNCAPPED WITH MLCAPE APPROACHING 2000 J/KG. CURRENT VAD DATA

INDICATE THAT 50 KT WLY WINDS HAVE OVERSPREAD THE REGION AT 6 KM AGL

WHICH IS RESULTING IN SUFFICIENT VERTICAL SHEAR FOR SUPERCELLS AND

BOWING STRUCTURES CAPABLE OF DAMAGING WINDS AND PERHAPS SOME HAIL.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT

TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM

MOTION VECTOR 27030.

...MEAD

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I wonder if this is a record number of consecutive days with watches for Philly?

 

 

I remember a time back in 2002 when I graduated from grade school where we had 4 or 5 watches in a weeks time but not consecutive days. Thats about the only time i can remember having a multipe severe risks for a week.

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