POSSIBLE AIRSPACE VIOLATION DUE TO LOWERING CLOUDS AND RAIN.

Narrative

FLT FROM MRY TO SQL. INTENDED TO FLY MOSS LNDG DIRECT OSI; THEN TO SQL. APCHING SANTA CRUZ; REALIZED THE CEILING WAS LOW OVER THE HILLS. ATTEMPTED TO GO UP THE VALLEY AND STAY BELOW THE CEILING. REALIZED I WAS BELOW THE RIDGE LINE ON MY L AND THE CEILING WAS NOT RISING. OPTED TO CROSS THE HILLS TO THE SJC SIDE. CONSIDERATIONS: WORRIED ABOUT BEING ON LEE SIDE OF THE HILLS WITH A CROSS-RIDGE WIND; AVOID SJC CLASS C. GOT TO SJC SIDE; FLYING N. CEILING DROPPED TO 0 DEAD AHEAD. TO AVOID CLOUDS NEEDED TO TURN TOWARD SJC. I WAS BTWN 2400 FT AND 2500 FT MSL AT THE TIME. I CALLED BAY APCH FOR PERMISSION TO ENTER THE CLASS C TO AVOID THE CLOUD. RADAR CONTACT AT (ABOUT) 7 MI FROM SJC. PROB: I MAY HAVE CLIPPED THE 2500 FT FLOOR OF THE CLASS C BEFORE I RECEIVED RADIO ACKNOWLEDGEMENT. LESSONS: 1) CFIT AND 'THE BOX CANYON MISTAKE' CAN SNEAK UP ANYTIME THE CEILING IS LOW. 2) CALLING ATC EARLY IS ALWAYS BETTER THAN CALLING THEM LATE. 3) A FORECAST OF 3000-5000 FT BROKEN OVER HILLS WITH A SAFE ALT OF 3900 FT SHOULD ALWAYS GET ATTN; EVEN IF THE CURRENT RPT IS 3000-5000 FT SCATTERED AND IMPROVING. 4) THE SF BAY AIRSPACE IS COMPLEX; THE PLT LOAD FOR JUST GETTING AROUND IS HIGH. IN A STRESS SIT IT'S NOT EASY. UPON FURTHER CONSIDERATION AND REF TO THE SF TERMINAL AREA CHART; I FEEL SURE I VIOLATED MOFFET'S CLASS D WHILE CIRCLING OVER I-280 WAITING FOR THE RAIN TO DISSIPATE AND GETTING SET UP TO CALL PAO FOR PERMISSION TO TRANSITION.