* Improved U.S. Midwest weather weighs on Chicago soybean futures * Wheat set to end week down for first time in 4 weeks (Recasts, adds details on fund positioning, updates prices) SINGAPORE, Aug 20 (Reuters) - Chicago soybean futures were on track for their biggest weekly drop in six weeks on Friday, as forecasts of rains in parts of the U.S. Midwest boosted hopes for better yields. Wheat lost ground for the first time in four weeks, although worries about global supplies kept a floor under the market. The most-active soybean contract on the Chicago Board Of Trade (CBOT) were up 0.3% at $13.24 a bushel by 0244 GMT, having closed down 2.5% on Thursday when prices hit an Aug. 4 low of $13.14-1/4 a bushel. Soybeans are down 3% for the week after closing up 2.1% in the previous week. Wheat has lost around 3% for the week and corn is down nearly 4% this week. Rains expected across northwestern portions of the U.S. Midwest could improve production prospects, particularly for soybeans. Corn yields and soybean pod counts in Illinois are projected to be above a three-year average, scouts on an annual tour found on Wednesday. Estimates for all of Iowa and Minnesota are expected later on Thursday. Improving export demand for U.S. soybeans underpinned futures. Export sales topped 2 million tonnes in the week ended Aug. 12, and the U.S. Department of Agriculture confirmed private sales of 263,000 tonnes of U.S. soybeans to China and 148,590 tonnes to Mexico. The wheat area in England for this year’s harvest rose 28% from 2020 to 1.62 million hectares, Britain’s farm ministry said on Thursday issuing provisional results of its June survey. Commodity funds were net sellers of CBOT soybean, corn, wheat, soyoil and soymeal futures contracts on Thursday, traders said. (Reporting by Naveen Thukral; editing by Uttaresh.V) Our Standards: The Thomson Reuters Trust Principles.