Retailers' holiday sales have so far proved disappointing, but online-sales again are a bright spot. After mall-traffic tracker ShopperTrak on Monday reported a 3.1% decline in holiday in-store sales and a 21% plunge in store traffic in the crucial shopping week ended Sunday, additional data again suggest a much brighter picture online. Total online sales from Friday through Sunday surged 37% year-to-year, with mobile traffic representing two-fifths of all online traffic, according to IBM Digital Analytics said. Consumers buying from their mobile devices sent mobile sales up 53%, accounting for 21.5% of all online sales, IBM said. The days between Friday and Sunday are important for the retail industry because they, along with Black Friday, represent the top four shopping days of the season, ShopperTrak said. Separately, online sales between Dec. 15 and Dec. 18 also jumped 13%, with 23% traffic growth, according to Custora Pulse, which tracks real-time data from more than 100 U.S. retailers selling online. However, while online growth continues to outpace the in-store growth, consumers still spend the bulk of their money at brick-and-mortar stores. The National Retail Federation forecast total holiday physical-store and online sales in November and December to total $602 billion, but its online Shop.org arm projected as much as $82 billion for Internet sales. With what looks to be a disappointing holiday season, Retail Metrics' Ken Perkins said Tuesday that fourth-quarter retail sales for the 120 chains it tracks is now expected to rise just an average of 1.9%, the weakest since third-quarter 2009. Profit growth is expected to be just 1.3%, also the weakest since third-quarter 2009, "when retailers were still clawing their way out of the Great Recession."