* Yellen says some data weak, weather impact uncertain
* Jobless claims up, durable goods top forecasts
* J.C. Penny, Best Buy rally after results
* Indexes: Dow and S&P 500 flat, Nasdaq up 0.2 pct
By Ryan Vlastelica
NEW YORK, Feb 27 (Reuters) - U.S. stocks were little changed on Thursday as comments from Federal Reserve Chair Janet Yellen failed to provide clarity on the impact of a harsh winter on recent economic weakness, while concerns rose over turmoil in Ukraine.
Addressing the Senate Banking Committee, Yellen said some economic data had been weaker since she spoke to the House of Representatives on Feb. 11, but that it was difficult to say how much of that was due to weather. Yellen also confirmed that the central bank would keep to its stimulus-trimming schedule.
The theory that some recent lackluster data was due to the weather rather than worsening fundamentals had helped investors shrug off the data and recently took the S&P 500 to a record high. However, the benchmark index has struggled to break decisively above its 2013 year-end closing level of 1,848.36, and trading could take a more pronounced turn to the downside on indications the economy is slowing.
In the latest economic report, orders for durable goods fell 1 percent in January, a drop that was less than forecast. However, jobless claims unexpectedly rose in the latest week.
"Durables came in better than feared, but it is difficult to tell what the weather impact was, and what the impact of an actual slowdown might be," said Joseph Tanious, global market strategist at J.P. Morgan Asset Management in New York. "I think we're in a cyclical slowdown now, and the weather isn't helping, although it should create pent-up demand."
Geopolitical tensions mounted after armed men seized the regional government headquarters and parliament in Ukraine's Crimea and raised the Russian flag. Ukraine's parliament appointed former economy minister Arseny Yatseniuk as prime minister, while ousted leader Viktor Yanukovich said he was still president in a statement sent to Russian news agencies from an unknown location.
The Ukraine uncertainty spurred investors to head for the safety of U.S. Treasuries, where yields fell to two-week lows.
"As an investor, you need to weigh the possibility of something going wrong against the probability of something going right," said Tanious. "It is a headwind to sentiment, but unless it has a big impact on oil, which I don't expect, we should work through it.
The Dow Jones industrial average was up 6.52 points, or 0.04 percent, at 16,204.93. The Standard & Poor's 500 Index was up 0.69 points, or 0.04 percent, at 1,845.85. The Nasdaq Composite Index was up 6.54 points, or 0.15 percent, at 4,298.61.
Both J.C. Penney Co Inc and Best Buy Co Inc jumped after posting strong results, with Penney late Wednesday forecasting more improvement in its comparable sales and gross profit margin this fiscal year and Best Buy posting adjusted earnings that topped forecasts.
Penney surged 21 percent to $7.23 while Best Buy advanced 5.4 percent to $27.22. The S&P retail index dipped 0.1 percent following a five-day rally.
Also on Thursday, Sears Holding Corp reported a quarterly loss that narrowed from the year-ago period, sending shares up 5.1 percent to $42.48, and Kohl's Corp said it expected modest sales gains in its new fiscal year and reported a lower fourth-quarter profit. Shares of Kohl's rose 1.3 percent to $55.14.