SEVERE WEATHER DISCUSSION FOR MONDAY, JULY 14TH, 2014

*** SEVERE WEATHER DISCUSSION FOR MONDAY, JULY 14, 2014 ***

HAVING REVIEWED THE SPC FORECAST GUIDANCE PRODUCTS, THERE APPEARS TO BE AT MODERATE RISK FOR SEVERE WEATHER ON MONDAY, 7/12/14.  NJ HAS BEEN OUTLOOKED BY THE STORM PREDICTION CENTER FOR MONDAY UNDER “SLIGHT RISK” AS WELL, AND THEREFORE, THIS IS BEING PUBLISHED FOR YOUR GUIDANCE.  AS OF TODAY, SATURDAY, THE SPC GUIDANCE SUGGESTS MOST UNSTABLE CAPE VALUES OF AT LEAST 1000J/KG AND UP TO 2000J/KG AT LEAST OVER CENTRAL AND WESTERN NJ, EXTENDING INTO SOUTHWEST AND COASTAL NJ AS THE DAY GOES ON.

 

 

SHEAR/CAPE EXIST FOR SUPERCELL DEVELOPMENT FROM A PERIOD STARTING MONDAY MORNING AROUND 11AM LASTING THROUGH TUESDAY 11AM (ACTUAL TIMES WILL LIKELY BE ADJUSTED PRIOR TO MONDAY). WE ARE ISSUING THIS GUIDANCE TODAY DUE TO THE NATURE OF THE DOUBLE COLD FRONT AND THE POSSIBILITY THAT THE POTENTIAL SEVERE WEATHER THREAT COULD POTENTIALLY INCREASE, OR DECREASE, DEPENDING ON HOW MUCH HEAT IS AVAILABLE ON MONDAY.  HERE IS THE OFFICIAL TEXT FROM THE SPC AND NWS FOR THE NJ/PHI AREA:

A TROUGH OF SUBSTANTIAL AMPLITUDE WILL EVOLVE ACROSS THE UPPER MS VALLEY AND GREAT LAKES REGIONS THROUGH MONDAY WITH THE GREATEST MID-LEVE HEIGHT FALLS OF 60-90M PER 12H FORECAST TO SPREAD FROM MN/WI TO MI/OH/INDIANA DURING THE PERIOD. A STRONG COLD FRONT ASSOCIATED WITH THE AMPLIFYING TROUGH IS FORECAST TO SPREAD EAST-SOUTHEAST FROM THE UPPER MIDWEST TO THE MIDDLE MS VALLEY THROUGH THE PERIOD WITH CYCLOGENESIS POSSIBLE ALONG THE FRONT OVER THE EASTERN GREAT LAKES...PER LATEST ECMWF (THIS REFERS TO THE MUCH DEBATED “POLAR VORTEX” OF JULY). 

THE FORECAST IS MADE MORE COMPLEX GIVEN A MORE DIFFUSE FRONT FROM NEW ENGLAND TO THE MID-ATLANTIC WILL PRECEDE THE STRONGER COLD FRONT...AND THERE ARE MODEL DIFFERENCES AS TO THE STRENGTH AND TIMING OF CYCLOGENESIS ALONG THE TRAILING FRONT...AND THE DEGREE OF AIRMASS DESTABILIZATION THAT WILL TAKE PLACE ALONG/NEAR BOTH BOUNDARIES AND THE DEVELOPING FRONTAL LOW.

MID MISSISSIPPI VALLEY TO NJ/PA/NY AND NORTHERN DELMARVA AREAS… GIVEN THE AFOREMENTIONED FORECAST COMPLEXITIES ONLY A BROAD ZONE OF RELATIVELY LOW SEVERE PROBABILITIES CAN BE DEPICTED IN THIS OUTLOOK. THE LEADING FRONT WILL BE INTERSPERSED WITH CONVECTIVE OUTFLOW…AND LIKELY ONGOING STORMS...THAT SHOULD SPREAD EAST NORTHEAST INTO A CORRIDOR OF INCREASING INSTABILITY. SHEAR AND FORCING AS DEPICTED IN BOTH NAM AND PARALLEL NAM...AS WELL AS GFS AND ECMWF...WOULD SUPPORT A FEW TO SEVERAL ORGANIZED STORMS WITH STRONG TO DAMAGING WINDS AND ALSO SOME TORNADO POTENTIAL. 

FOR NJ / PA SPECIFICALLY, ON MONDAY, THE ENTIRE EASTERN SEABOARD WILL BE POSITIONED WITHIN THE PRE-FRONTAL WARM SECTOR THAT IS WELL AHEAD OF THE GREAT LAKES UPPER LOW AND ATTENDANT COLD  . HOT AND HUMID ARE FORECAST WITH SLY RETURN FLOW AROUND THE HIGH AND THE LLVL THERMAL RIDGE OVERHEAD. HOWEVER, THE EXTENT OF LEFTOVER DEBRIS CLOUDS FROM OVERNIGHT CONVECTION IS UNCERTAIN, BUT IF CLOUDS LINGER LATER INTO THE DAY THAN CURRENTLY ANTICIPATED, FORECAST MAX TEMPS IN THE LOWER 90S MAY NOT BE REALIZED. ASSUMING SUFFICIENT BREAKS IN CLOUD COVER DO OCCUR, MODERATE TO STRONG INSTABILITY WOULD DEVELOP OVER THE REGION (MEDIAN SBCAPE FROM THE 09Z SREF ARE 1500-2000 J/KG) WOULD LIKELY DEVELOP ALONG A SHARPENING LEE SFC TROUGH DURING THE AFTERNOON. STRONGER SW WINDS ALOFT WILL SPREAD EASTWARD AHEAD OF THE TROUGH, HELPING TO INCREASE DEEP-LAYER SHEAR OVER THE AREA (FCST MEDIAN 0-6 KM SHEAR FROM THE 09Z SREF INCREASES TO 40 KT ACROSS NERN PA LATE IN THE DAY). THERE IS A POTENTIAL FOR SEVERE THUNDERSTORMS MONDAY AFTERNOON AND EVENING GIVEN THE FORECAST ENVIRONMENT. THE AREA IS OUTLOOKED IN A SLIGHT RISK BY SPC FOR MONDAY. DAMAGING WINDS WOULD BE THE PRIMARY THREAT BUT LARGE HAIL, ISOLATED TORNADOES AND FLASH FLOODING ARE ALSO POSSIBLE.

APPROACHING COLD FRONT ON SUNDAY 8PM

FRONTAL BOUNDARY / PRECIPITATION APPROXIMATELY 8AM IN NORTHWEST NJ... A BIT LATER FOR CENTRAL/SOUTHERN NJ.... TIMES MAY CHANGE PRIOR TO MONDAY 7/14/14