Lag Baomer is probably the only true outdoor festival of the Jewish calendar Tu B'Shvat, the New Year for Trees, was also reinstituted in modern Israel as such, but includes home customs for family and inclement weather!. Lag ba-Omer is the 33rd day of the counting of the Omer, which starts on the second night of Pesach and ends on Shavuot.
Lag Baomer in 2015 is on Thursday, the 7th of May.