The winning streak is expected to continue into its sixth day on Tuesday as traders continue to build positions ahead of the Christmas break.City sources predict the FTSE 100 will open around 33 points higher than Monday's close of 6,576.74.Five straight days of gains sent the index to its highest closing level in two weeks. The last time it finished above this mark was on 8 December.While trading volumes are expected to be low on Tuesday, there will be a barrage of economic data to keep those remaining traders on the market busy.The final estimate of UK gross domestic product (GDP) is forecast to confirm that year-on-year growth was 3% in the third quarter.US GDP is also out but is expected to be revised to show 4.3% annualised growth in the third quarter, up from the previous estimate of 3.9%.US durable goods, consumer confidence, new home sales and personal spending figures are also on tap for Tuesday afternoon.Stocks to watchAnnual profits will be lower than expected at Thorntons as the confectioner warned of a "significant reduction" in orders from major supermarkets and a problem with its warehouse distribution. The manufacturer and retailer said that it expected earnings for the full year to be "below those achieved for the last financial year" but that the performance from grocers overall had not been all bad with good growth in several sectors.Outsourcing company Capita has appointed Halma's boss Andrew Williams to its board as an independent non-executive director. Williams, who has been the chief executive of safety, health and environmental technologies group Halma since February 2005, will join the FTSE 100 company on 1 January 2015.