CAPT OF AN SMT HELI INADVERTENTLY PENETRATED CLASS B AIRSPACE DUE TO DETERIORATING WX CONDITIONS.

Narrative

THE WX WAS ORIGINALLY FORECAST TO BE MARGINAL VFR THROUGHOUT NEW JERSEY THIS DATE. HOWEVER; THE WX MADE A VERY ABRUPT TURN FOR THE WORSE IN MINS. SEVERE WX WAS ERUPTING ALL OVER SOUTH JERSEY SURPRISING EVERYONE. I HAD LEFT WILMINGTON; DE; EBOUND VFR WITH SEVERAL SMALL TSTM CELLS SHOWING ON MY RADAR TO THE E AND SE. SUDDENLY; THE SCREEN LIT UP WITH SEVERE WX IN ALL AREAS. I WAS AT THAT TIME FOLLOWING THE NEW JERSEY TURNPIKE AND ALSO USING LORAN AND VOR NAV. VISIBILITY GOT VERY LOW AND I CIRCLED VFR WHERE I THOUGHT I WAS STILL CLR OF PHILADELPHIA CLASS B AIRSPACE. I CONTACTED THE APCH CTLR; ADVISED HIM OF MY CONDITIONS AND ASKED FOR IFR ROUTING BACK TO WILMINGTON. AT THAT TIME HE ADVISED ME THAT I HAD PENETRATED PHILADELPHIA CLASS B AND WAS 4.8 NM S OF PHILADELPHIA. I TOLD HIM I WAS AVOIDING HVY WX AND INADVERTENTLY ENTERED; UNKNOWN TO ME. HE THEN CLRED ME BACK TO WILMINGTON; IFR. HE ALSO STATED MY INTRUSION WAS NO BIG DEAL AND THAT EVERYONE WAS SURPRISED BY THE INSTANT WX CHANGE GOING ON. MY CONCERN WAS KEEPING MYSELF; PAX; AND ACFT SAFE AT THIS TIME AND OBTAINING AN IFR CLRNC TO AVOID AN ACCIDENT; ETC.