I would consider upgrading that extension cord.. Sears (And K-Mart) both sell a 12ga cord which is designed for indoor/outdoor use, This cord is different from the nearly identical cords sold at Home Depot, lowes. Ace Hardware and .. most everywhere else, in that there is a push button on the outlet end that must be pushed when plugging into the cord or unplugging from it.
Thus I recommend it
But any good 12ga cord is better than the 14 or 16Ga "Standard" cords.
I have 3 of those 12ga cords
one is 100 ', the others are 10 and 20.