Wheat futures on the Chicago Board of Trade crept higher for a fourth straight session on Friday, supported by a weaker US dollar and higher-than-expected weekly US wheat export sales, traders said. CBOT grain trade closed two hours early because of the US Thanksgiving holiday weekend. CBOT December options expired at the close, with moderate open interest at the $8.50 strike helping to keep front-month wheat futures from falling very far below that level. For the week, CBOT wheat ended up 1.1 percent, rebounding from a 5.5 percent loss the previous week. USDA reported export sales of US wheat in the latest week at 657,500 tonnes (635,500 for 2012/13), above a range of trade estimates for 200,000 to 400,000 tonnes. Weak dollar lends support. Optimism about a deal to help Greece, hopes that US lawmakers can agree on a solution to avoid a fiscal crisis, and data showing an improving global economic outlook have pressured the dollar and driven a rally in riskier asset markets, including commodities, this week. Argentina's government on Thursday cut its 2012/13 wheat output forecast to 11.1 million tonnes, from 11.5 million previously, citing months of heavy rains and flooding. Ukraine's grain traders are ready to halt milling wheat exports on an informal basis as they approach a critical limit, in order to protect the domestic market after a poor harvest, the agriculture ministry said on Friday. Brazilian buyers may have made a rare purchase of German wheat in response to lower supply from its main source Argentina, European traders and analysts said.