NEW YORK — Will Santa’s sleigh be late?

A record number of Americans took to the Web to order holiday gifts after retailers flooded their inboxes with offers of extra discounts, free shipping and easy returns.

But a storm bringing heavy winds and snow to much of the Midwest on Thursday – the heaviest shipping day of the year – could mean some packages might not make it under the tree in time for Christmas.

That’s a headache for retailers, shippers and customers alike who already were experiencing problems because of the surge in shipping this year.

So far, no major disruptions have been reported.

Wal-Mart, the No. 2 online retailer behind Amazon.com, said no orders have been delayed. GSI Commerce, which handles online shipping for 70 retailers, said it is monitoring the situation hour-by-hour and so far, deliveries are being made on time. By the time the storm hits the Northeast today, it should be a wintry mix of rain and snow – nothing to delay deliveries.

Still, the storm’s timing couldn’t be worse for the world’s largest package delivery company, UPS. Thursday was the Atlanta-based company’s busiest day of the year. Before the storm shut down service in some areas, it expected to move 28 million packages on Thursday, nearly double an average day.

Both UPS and smaller rival FedEx Corp., based in Memphis, Tenn., have extensive contingency plans for blizzards and other inclement weather, including scores of meteorologists on staff to redirect planes and trucks and planes at the ready to replace others that can’t take off.

The storm led UPS to halt all pickups and deliveries in some parts of Iowa and Nebraska. It had to re-route packages destined for the Des Moines airport, from which many shipments then are moved by truck to their final destinations across the Plains states. Instead, it’s moving those shipments out of its hub in Louisville, Ky., until the skies and roads clear.

Nine out of 10 retailers planned to offer free holiday shipping, according to Shop.org, which is part of trade group The National Retail Federation.

And free shipping wasn’t just an incentive for early shoppers. More than 46 percent of the major online retailers emailed their subscribers on Monday Dec. 17, a.k.a. free shipping day, with offers to ship gifts free with no minimum purchase. Fewer than 10 percent made that offer last year, according to marketing software company Responsys.

That spurred shoppers to spend more – online shopping is expected to have risen 17 percent this holiday season to a record $43.4 billion, according to comScore.

Karla Neville, 31, who works in national event marketing in New York, was enticed by Gap’s offer of 30 percent off everything. She ordered a sweater, belt and tie for her husband from Banana Republic’s website, which is owned by Gap Inc.

Gap separated the order into two and sent the sweater and tie by FedEx and the belt by UPS. Neville never received the belt, discovering online that the UPS package had been returned to Gap for reasons unknown. She doesn’t want the belt anymore, just a refund.