By Jennifer Waters, MarketWatch

CHICAGO (MarketWatch) -- Ever notice how the things you need most in sweltering heat -- a bottle of water, ice cream -- seem to be everywhere you turn?

It's not by accident. Retailers keep close watch on the weather to market must-have-now items in hopes that you'll wander in and pick up other things up along the way.

These are not necessarily sale items, but traffic drivers that work to lure consumers in like a fat worm bobbing on a hook in the water attracts a fish. Unlike fish though, consumers can choose not to take the bait.

"Retailers use the weather as an inside tip to anticipate shopper behavior and to plan pricing," said Evan Gold, senior vice president at Planalytics, which charts weather patterns for businesses.

"From an inventory perspective, they need to know when is the customer going to come in and for what so they've got the product there," he said. "When people need something and it's not on the shelf, they'll go to another store. It's a competitive measure."