After several weeks of persistent cold and widespread winter hazards, weather conditions across much of the United States are beginning to moderate as the overall atmospheric pattern shifts. Forecasters report that a strengthening ridge of high pressure is developing over large portions of the country, allowing milder air masses to advance northward and gradually replace the Arctic air that dominated January. The transition marks the first broad return to above-average temperatures in weeks a

WASHINGTON — A prolonged stretch of frigid temperatures has gripped the Washington, D.C., region, leaving portions of the Potomac River covered in ice and prompting renewed safety warnings from local authorities who say the frozen surface is far more dangerous than it appears. Officials report that the recent cold snap has caused sections of the river near the Georgetown waterfront to freeze over, creating the illusion of a solid walking surface. Police say they have already recei