Once the pumpkin pie is polished off on Nov. 28, many consumers will turn to the web in their feast-induced comas to start searching for holiday gifts, according to new research from Adobe Systems Inc.

Its just-released Adobe Digital Index forecasts record growth for online sales on Thanksgiving, with web sales reaching $1.1 billion, up 21.0% over $909 million on the holiday last year. On two historically big shopping days—Black Friday, the day after Thanksgiving, and Cyber Monday, the Monday after Thanksgiving—Adobe also predicts strong web sales growth. For Black Friday, it forecasts e-retail sales will reach $1.60 billion, a 17.6% increase compared with $1.36 billion for the same day last year. For Cyber Monday, Adobe predicts consumers will spend $2.27 billion online, a 15.2% increase compared to $1.97 billion on the same day in 2012.

The forecast is derived from the Adobe Digital Index, which is based on the analysis of nearly half a trillion visits to more than 2,000 retail web sites over the last seven years.

But the news isn’t all merry and bright. The shorter holiday shopping season will result in missed sales overall, Adobe says. This year, there are only 26 days between Thanksgiving and Christmas, compared with 32 days in 2012. What’s more, consumers have four—not five—full weekends in that timeframe to snag gifts. Adobe predicts the slimmer season will cost retailers $1.5 billion in missed online sales.

“Thanksgiving Day, Black Friday and Cyber Monday will all enjoy record online sales,” says Brad Rencher, senior vice president, digital marketing business, Adobe. “Thanksgiving Day sales are projected to surpass $1 billion and could overtake Black Friday within the next five years. The growing importance of Thanksgiving Day, the shortened holiday season and the growing role of mobile and social will make 2013 a very different shopping season.”

As part of its holiday research, Adobe also surveyed 400 consumers who plan to buy at least some of their holiday gifts online this year. The research reveals that 20% of online transactions will stem from a consumer using a smartphone or tablet at a mobile optimized site or app, up 47% year over year. Mobile sales will account for 14% of web revenue, up 40% from the holiday season last year, Adobe says. And consumers will likely extend their mobile shopping to stores. Nearly 40% of shoppers polled say they have shopped online while in a store. 22% of consumers say they have checked a price online via their mobile devices while in a store–and among 18 to 34 year-olds, that figure rises to 35%, Adobe says.

Consumers say they will most likely shop online for apparel and accessories, followed closely by books, music, videos and toy and hobby items. Additionally, 36% of consumers surveyed say they plan to turn to social media sites for help in deciding what to buy.