Narrative:

ATIS at XX45Z, balloon report at XX09Z, visibility 6 mi with haze, 250 broken, 240 at 18, 29.95, ILS runway 23. While being vectored for an ILS runway 23, at 2000 ft, on a right downwind for runway 23, in very marginal conditions, I observed traffic at approximately 45 degrees from head-on, 200 ft lower, cross the approach end of runway 23 and pass slightly behind me. Obviously a transient with no idea where he was. New york approach did warn me of his presence. 18 mins later I was cleared for takeoff on runway 23. Clearance was climb to 2000 ft, turn left to 180 degrees, cleared for takeoff. While in a climb at approximately 1300 ft and in a left turn to 180 degrees, I saw traffic directly under me, from right to left approximately 100 ft lower. This was the second close call within 18 mins. The visibility was questionable, especially in the north quadrant, yet the traffic pattern was inundated with VFR traffic. I realize it's up to me to maintain separation in VFR conditions, but would a prudent ATC controller clear you for takeoff with an aircraft about to enter downwind for the same runway. Once I started my left turn I lost most of my visibility from the right.

Related reports:

Google
 

Original NASA ASRS Text

Title: PLT OF SMT ON ARR AND DEP ON AN IFR FLT PLAN HAS NMAC WITH OTHER ACFT PASSING THROUGH TFC PATTERN AREA. NO TIME FOR ANY ACTION.

Narrative: ATIS AT XX45Z, BALLOON RPT AT XX09Z, VISIBILITY 6 MI WITH HAZE, 250 BROKEN, 240 AT 18, 29.95, ILS RWY 23. WHILE BEING VECTORED FOR AN ILS RWY 23, AT 2000 FT, ON A R DOWNWIND FOR RWY 23, IN VERY MARGINAL CONDITIONS, I OBSERVED TFC AT APPROX 45 DEGS FROM HEAD-ON, 200 FT LOWER, CROSS THE APCH END OF RWY 23 AND PASS SLIGHTLY BEHIND ME. OBVIOUSLY A TRANSIENT WITH NO IDEA WHERE HE WAS. NEW YORK APCH DID WARN ME OF HIS PRESENCE. 18 MINS LATER I WAS CLRED FOR TKOF ON RWY 23. CLRNC WAS CLB TO 2000 FT, TURN L TO 180 DEGS, CLRED FOR TKOF. WHILE IN A CLB AT APPROX 1300 FT AND IN A L TURN TO 180 DEGS, I SAW TFC DIRECTLY UNDER ME, FROM R TO L APPROX 100 FT LOWER. THIS WAS THE SECOND CLOSE CALL WITHIN 18 MINS. THE VISIBILITY WAS QUESTIONABLE, ESPECIALLY IN THE N QUADRANT, YET THE TFC PATTERN WAS INUNDATED WITH VFR TFC. I REALIZE IT'S UP TO ME TO MAINTAIN SEPARATION IN VFR CONDITIONS, BUT WOULD A PRUDENT ATC CTLR CLR YOU FOR TKOF WITH AN ACFT ABOUT TO ENTER DOWNWIND FOR THE SAME RWY. ONCE I STARTED MY L TURN I LOST MOST OF MY VISIBILITY FROM THE R.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.