NON INST RATED PVT PLT SPIRALED DOWN THROUGH A HOLE IN THE UNDERCAST TO GO ENRTE UNDERNEATH. HOWEVER; WHEN HE HAD INSUFFICIENT CLOUD CLRNC AND VISIBILITY; HE SPIRALED BACK UP. APCH CTLR RECOMMENDED THAT HE DSND 1000 FT TO AVOID IFR TFC NEARBY.

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I CHKED WX BEFORE I LEFT PAO BY 3 HRS (5 HRS TOTAL) AND THE CENTRAL VALLEY WAS TO BE A MESS WITH HAZE; BUT SOCAL WAS TO BE FINE FOR VFR INTO FUL. I SHOULD HAVE CHKED THE WX ENRTE OR JUST BEFORE I LEFT. I FOLLOWED I-5 FROM GRAPEVINE TO CASTAIC BY WHICH TIME IT WAS OBVIOUS THAT THE ENTIRE LOS ANGELES BASIN WAS COVERED BY A LAYER AT 3100 FT. I TOLD THE CTLR THAT I WOULD LIKE TO FOLLOW I-5 TO FUL AND HE SAID THAT MAY BE POSSIBLE AT 2000 FT. I SAID FINE AND RESPONDED THAT I SAW A HOLE AT 10 MI AHEAD. WHEN I DROPPED DOWN; IT WAS LOW VISIBILITY; BUT NOT TECHNICALLY IFR (3-5 MI; HAZE). HAVING NO DESIRE TO NAV THAT TO FUL I RETURNED TO APPROX 7500 FT BY SPIRALING. ON THE WAY UP; THE CTLR GOT ME BACK ON RADAR AND RADIO COM. HE INFORMED ME I WAS UNDER THE VNY APCH PATH AND A GULFSTREAM AND CITATION WERE ABOVE ME AND TO STAY BELOW 6500 FT FOR THE MOMENT AND THAT I COULD RESUME OWN NAV. I HEADED NE. AFTER THE TFC WAS NO FACTOR; I WAS TOLD TO SQUAWK 1200. I THEN HEADED TO WJF; LANDED; AND RENTED A CAR. HUMAN FACTORS: WHEN I SAW THE CLOUD LAYER MY FIRST THOUGHT WAS BFL UNTIL I SAW THE HOLE. BEFORE I DROPPED DOWN I HAD DECIDED TO DIVERT IF IT WASN'T CLR BELOW THE LAYER. THE HOLE WAS LONG AND NARROW SO I MAY HAVE MOVED FARTHER E OR W THEN I REALIZED TO END UP IN THE APCH PATH WHEN I WAS CIRCLING TO SEE THE CONDITIONS. WHEN LOOKING AT THE CHART TO DIVERT TO BFL I NOTICED WJF WAS CLOSER AND WENT THERE INSTEAD.