Retailers are counting on time-crunched shoppers to swarm stores on Super Saturday, but a heavy winter storm threatened to strand them at home on the final weekend before Christmas.

This weekend marks the beginning of the longest 'last minute' as shoppers start to get really serious about their holiday shopping, said Marshal Cohen, chief industry analyst at the NPD Group.

But nobody is predicting a blow-out year for holiday sales because consumers are still under pressure from a double-digit unemployment rate and a weak economy.

Retailers have worked to avoid a repeat of last year, when a global economic meltdown left them buried in excess merchandise and desperate to make a sale at almost any price.

But despite their careful planning, a winter storm expected along the eastern U.S. coast is clouding this weekend's sales prospects.

A serious snow storm is threatening parts of the east coast, its track running from Virginia north to Boston, according to weather tracking company Planalytics.

We believe retail sales will likely suffer as the sales lost during what historically has been the busiest weekend of the year will not be recovered. You can't make up for lost days, Stifel Nicolaus analyst Richard Jaffe wrote in a note on Friday.

Also, Christmas falls on a Friday this year, which could shift last-minute gift buying into next week, when snow and rain are expected in various parts of the United States.

Jaffe and others said storms could drive consumers to shop online. While that could be a boon for sites such as Amazon.com , consumers may have to pay unwanted last-minute shipping fees to ensure gifts arrive by December 25.

On Friday afternoon, Gap Inc noted on its site that shoppers could order online until December 23 to get gifts on time.

Those still trying to finish their shopping appear to be waiting for steeper discounts.

There's always going to be a step up in the promotions in the days before the holiday, and there's going to be some clearance after the holiday, said Cowen & Co analyst Laura Champine. I do think it will be less promotional ... it's a really gradual training of the customer to buy closer to full price.

Holiday sales forecasts have narrowed over the course of the shopping season to a range of down 1 percent to up 1 percent from 2008, when sales fell for the first time since the National Retail Federation started tracking the data.

Consumers surveyed in late November by Consumer Edge Research said they planned to spend an average of $402 on gifts this season. That was down from the $440 those polled in October said they were planning for.

Retail sales Marketing Christmas Storm