Usually Dec 15 - Jan 15, but Nov and Feb remain outlying possibilities.
The following two make interesting reading side by side:
Nov 21, 2010 "Fog delays unlikely this winter as airlines train more pilots"
http://www.thaindian.com/newsportal/...100278018.html
Nov 26. 2010 "Fog delays flights at Delhi’s IGI airport"
http://www.theindiadaily.com/fog-del...is-igi-airport