C172 PLT ENTERS IMC WHILE VFR IN THE DC ADIZ.

Narrative

I WAS FLYING IN VMC; FINISHING A SHIFT DOING TFC WATCH OVER BALTIMORE; AND MONITORED THE AWOS AT GAI ON THE WAY INTO OUR USUAL REFUELING POINT; CGS. THE AWOS HAD BEEN SAYING 008 SCATTERED; 017 BROKEN FOR A WHILE; AND WAS NOT FORECAST TO GO TO IFR (BROKEN BELOW 1000 FT AGL) UNTIL MUCH LATER. I LANDED AT CGS TO GET FUEL AND WAS BACK UP 15 MINS LATER FOR THE 10 MIN; 15 NM FLT BACK TO GAI. WITHIN ABOUT 4 MI OF GAI (A POINT I KNEW WELL BY THE ROADS OVER WHICH I WAS FLYING); THE CEILINGS WENT FROM FEW AT 800 FT TO BROKEN AT 800 FT. I FOUND MYSELF DODGING MORE CLOUDS; AND ASKED WASHINGTON TWR; WHO CTLS ALL TFC WITHIN THE 'FRZ' AROUND WASHINGTON; FOR A SVFR CLRNC. THEY TOLD ME TO CONTACT POTOMAC ON 124.7 -- A FREQ I HAD NEVER USED BEFORE; IN OVER 600 HRS OF LCL FLT THIS YR. I TRIED TO GET A WORD IN ON 124.7; BUT THERE WAS NO RESPONSE -- THE AIRLINE TFC WAS TOO BUSY; AND I WAS TOO LOW. I COULD NOT GET AN IFR CLRNC WITHOUT FIRST CLBING (INTO THE BROKEN LAYER); SO I CHOSE TO FLY THE KNOWN RTE; AT 700 FT AGL FOR THE LAST 3 MI BACK TO GAITHERSBURG; RATHER THAN RISK CLBING INTO THE CLOUDS; AND LOSING MY IMMEDIATE BEARINGS; ESPECIALLY THAT CLOSE TO THE 'FRZ' AND THE AIRSPACE AROUND WASHINGTON.