* Investors look to Yellen for insight into weather impact
* Weekly jobless claims, Jan durable goods data on tap
* J.C. Penney and Best Buy rally in premarket after results
* Futures down: Dow 48 pts, S&P 5.4 pts, Nasdaq 6.75 pts
By Ryan Vlastelica
NEW YORK, Feb 27 (Reuters) - U.S. stock index futures fell on Thursday, with the S&P 500 poised to recede further from record levels amid political uncertainty in Ukraine and ahead of comments from Federal Reserve Chair Janet Yellen.
* Investor concerns about geopolitical tensions mounted after armed men seized the regional government headquarters and parliament in Ukraine's Crimea and raised the Russian flag. Kiev's new rulers urged Moscow not to abuse its navy base rights on the peninsula by moving troops around.
* Yellen will address the Senate Banking Committee in a semiannual testimony about monetary policy, and investors are especially looking for insight into how an unexpectedly harsh winter has impacted economic activity. Yellen's appearance, originally scheduled for Feb. 13, was postponed because of a snowstorm.
* Recent data has largely come in under expectations, with a few bright spots, such as January new home sales. Many analysts have chalked the misses to the impact of weather instead of worsening fundamentals, a theory that has helped indexes shrug off the disappointments and send the S&P 500 to a record high earlier this week.
* There are concerns the data reflects a more bearish economic picture, and the S&P has struggled to break decisively above its 2013 year-end closing level of 1,848.36. If Yellen does not reassure market participants about the state of economic growth, trading could take a more pronounced turn to the downside.
* The market is also looking for confirmation the central bank will maintain its stimulus-trimming schedule, though no changes are expected to be announced in the testimony, which begins at 10:00 a.m. EST (1500 GMT)
* S&P 500 futures fell 5.4 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures fell 48 points and Nasdaq 100 futures slid 6.75 points.
* In retail news, both J.C. Penney Co Inc and Best Buy Co Inc jumped in premarket trading after their results. Penney gained 26 percent to $7.45, while Best Buy rose 2.3 percent to $26.41.
* Penney late Wednesday forecast more improvement in its comparable sales and gross profit margin this fiscal year, while Best Buy posted adjusted earnings that topped forecasts.
* Retail stocks have performed well recently, rising for five straight sessions on the back of some strong results, including from Home Depot and Macy's Inc.
* Also on Thursday, Sears Holding Corp reported a quarterly loss that narrowed from the year-ago period and Kohl's Corp said it expected modest sales gains in its new fiscal year and reported a lower fourth-quarter profit.
* Ahead of Yellen's testimony, traders will digest data on both weekly jobless claims and January durable goods. Claims are seen falling by 1,000 to 335,000 in the latest week, while orders for durable goods are seen down 1.5 percent. The data is scheduled for release at 8:30 a.m. EST.