M20T PLT ENCOUNTERS ADVERSE WX VFR ENRTE; REQUESTS IFR CLRNC FROM ZDC; THEN CLBS TO AVOID WX WITHOUT CTLR NOTIFICATION.

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I WAS ON AN IFR FLT PLAN TO RICHMOND; VA (RIC) AND HAD BEEN CLRED (GPS DIRECT) TO RICHMOND AT 11000 FT MSL. I KNEW OF TSTMS ACROSS MY RTE OF FLT AND HAD CONTACTED FLT WATCH TO LEARN THE CELL LOCATIONS. AT THE RECOMMENDATION OF FLT SVC BRIEFER; I HAD MODIFIED MY RTE TO A MORE SOUTHERLY HDG IN ORDER TO PASS S OF THE CONVECTIVE ACTIVITY. NEARING THE LINE OF STORMS; MY STORMSCOPE SHOWED NO ACTIVITY AHEAD AND THOUGHT I COULD SEE A VISUAL RTE BTWN A LARGE THUNDERHEAD TO THE N AND A SMALLER CUMULUS CLOUD TO THE S. AS I APCHED CLOSER TO THE CLOUDS; THE STORMSCOPE INDICATED MORE ACTIVITY AND IT BECAME APPARENT THAT I WOULD NOT BE ABLE TO MAINTAIN VISUAL CONDITIONS AT MY ASSIGNED ALT. THE CLOUDS APPEARED SCARY AND I WANTED TO MAINTAIN VISUAL CONDITIONS TO AVOID INADVERTENTLY FLYING INTO A TSTM CELL. BEFORE PENETRATING THE CLOUD MASS; I MADE A 90 DEG R TURN TO A SOUTHWESTERLY HDG AT WHICH I COULD FLY PARALLEL TO THE CLOUD MASS. I IMMEDIATELY CONTACTED ATC AND REQUESTED A CLB TO 15000 FT IN ORDER TO CLR THE CLOUDS TO THE E. THE CTLR SAID I SHOULD HAVE REQUESTED A DEV EARLIER; BUT SOON CLRED ME TO 15000 FT. WHILE CLBING; I TURNED BACK ON COURSE AND CONNECTED MY OXYGEN NASAL CANNULA. UNABLE TO MAINTAIN VMC AT 15000 FT AND CONCERNED ABOUT ICING SHOULD I PENETRATE A CLOUD; I CHOSE TO CONTINUE CLBING TO TOP OF CLOUDS AT ABOUT 16300 FT. THIS WAS QUICKLY NOTED BY THE CTLR; AND I ADVISED THEM I WOULD RETURN TO THE ASSIGNED ALT AS SOON AS I COULD. I WAS ABLE TO DSND BACK TO 15000 FT ABOUT 4 MINS LATER. AS I WAS 'HANDED OFF' TO THE NEXT CTLR; I APOLOGIZED FOR THE DEV; AND WAS SUBSEQUENTLY CHASTISED BY THE CTLR FOR MY DEVS. I COMPLETED THE FLT WITHOUT FURTHER INCIDENT. IN RETROSPECT; I SHOULD HAVE PLANNED A MORE SOUTHERLY COURSE TO FLY WELL S OF THE AREA OF POSSIBLE SEVERE WX. I COULD ALSO HAVE REQUESTED A 'BLOCK ALT' OR 'VFR ON-TOP' CLRNC; WHICH WOULD HAVE ALLOWED ME TO CLB TO THE ALT I NEEDED TO GET OVER THE WX. BY NOT KNOWING THE LATERAL EXTENT OF THESE CLOUDS AND NOT FULLY APPRECIATING THEIR HT; I WAS FORCED TO MAKE LAST-MIN COURSE AND ALT CHANGES; WHICH IRRITATED ATC. I WAS FORTUNATE TO HAVE A TURBO-CHARGED AIRPLANE WHICH ENABLED ME TO CLB OVER THE WX AND REMAIN 'VISUAL;' WHERE I COULD SEE THE STORMS AND OR OTHER ACFT. OF COURSE; ANY OTHER ACFT HAD WISELY CHOSEN TO AVOID THAT AREA OF WX ALTOGETHER.