FOR MORE THAN A CENTURY, THE NATIONAL WEATHER SERVICE HAS ISSUED ITS FORECASTS IN ALL CAPITAL LETTERS. But in the age of social media that’s considered yelling, so next month federal meteorologists are lowering their voices and their letters — except in dire emergencies. Weather service spokeswoman Susan Buchanan said the agency started using all capital letters in 1849 forecasts because of the telegraph. Twenty years ago, the agency tried phasing out the practice, but old equipment wouldn’t recognize lower-case letters. …