338  
ACUS11 KWNS 121802  
SWOMCD  
SPC MCD 121802  
NJZ000-PAZ000-MDZ000-DEZ000-VAZ000-DCZ000-WVZ000-122000-  
 
MESOSCALE DISCUSSION 1964  
NWS STORM PREDICTION CENTER NORMAN OK  
0102 PM CDT THU SEP 12 2019  
 
AREAS AFFECTED...SOUTHERN PA AND PORTIONS OF THE MID-ATLANTIC  
 
CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE  
 
VALID 121802Z - 122000Z  
 
PROBABILITY OF WATCH ISSUANCE...40 PERCENT  
 
SUMMARY...THUNDERSTORMS ARE EXPECTED TO DEVELOP OVER THE NEXT 1-2  
HOURS AND SOUTHEAST ACROSS THE MID-ATLANTIC/CHESAPEAKE BAY AREA  
THROUGH THIS EVENING. STRONG WIND GUSTS WILL BE THE MAIN CONCERN  
WITH THIS ACTIVITY, AND A WATCH MAY BE NEEDED THIS AFTERNOON.  
 
DISCUSSION...STRONG HEATING AHEAD OF A SOUTHWARD SAGGING COLD FRONT  
HAS RESULTED IN TEMPERATURES CLIMBING INTO THE MID 80S TO LOW 90S  
THIS AFTERNOON. A VERY MOIST AIRMASS WITH DEWPOINTS GENERALLY IN THE  
UPPER 60S TO LOW 70S IS IN PLACE, RESULTING IN MLCAPE VALUES AROUND  
1000-2000 J/KG. UPPER LEVEL FORCING IS WEAK ACROSS THE REGION, WITH  
CONVECTIVE DEVELOPMENT MAINLY DUE TO HEATING ALONG THE FRONT AND  
WEAK CONFLUENCE ALONG A SURFACE TROUGH FURTHER SOUTH IN THE  
CHESAPEAKE BAY VICINITY. EFFECTIVE SHEAR WILL REMAIN MODEST, AROUND  
25-30 KT, BUT IN THE PRESENCE OF MODERATE INSTABILITY THIS SHOULD BE  
SUFFICIENT FOR SUSTAINED, ORGANIZED UPDRAFTS. THE MAIN CONCERN THIS  
AFTERNOON INTO THIS EVENING WILL BE STRONG WIND GUSTS. LOW LEVEL  
THERMODYNAMIC PROFILES SHOW INVERTED-V SIGNATURES WHILE 17Z  
MESOANALYSIS INDICATED VERY STEEP LOW LEVEL LAPSE RATES. STORMS MAY  
ORGANIZE INTO A FORWARD PROPAGATING CLUSTER/BOWING SEGMENT THROUGH  
OUTFLOW INTERACTIONS/STORM MERGERS, INCREASING DAMAGING WIND  
POTENTIAL IF THIS OCCURS, THOUGH CONVECTIVE COVERAGE MAY REMAIN TOO  
ISOLATED IN THE ABSENCE OF STRONGER ASCENT. THUNDERSTORMS WILL  
SPREAD SOUTHEAST TOWARD THE I-95 CORRIDOR AND MID-ATLANTIC COAST  
THROUGH THIS EVENING. TRENDS WILL BE MONITORED AND A WATCH MAY BE  
NEEDED THIS AFTERNOON.  
 
FURTHER SOUTH TOWARD SOUTHEAST VA INTO NORTHEAST NC, MORE ISOLATED  
PULSE-TYPE STORMS ARE POSSIBLE WHERE LOW LEVEL CONVERGENCE ALONG THE  
SURFACE TROUGH MORE APPARENT. WEAK DEEP LAYER FLOW AND A LACK OF  
STRONGER ASCENT SHOULD LIMIT ORGANIZED CONVECTION, THROUGH A COUPLE  
OF STRONG GUSTS CAN NOT BE RULED OUT.  
 
..LEITMAN/HART.. 09/12/2019  
   
..PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT
 
 
ATTN...WFO...PHI...BGM...AKQ...CTP...LWX...  
 
LAT...LON 41467752 40457475 39477401 38567464 36687529 36607579  
36817652 37387725 39287805 40307838 40877826 41207813  
41467752  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab SPC Page Main Text Page