Here is the lastest National Weather Service Hydrometeorological Prediction Center Discussion:
SHORT RANGE FORECAST DISCUSSIONNWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD202 PM EST FRI DEC 18 2009 VALID 00Z SAT DEC 19 2009 - 12Z SUN DEC 20 2009
HEAVY RAIN CONTINUES TO CAUSE FLOODING CONDITIONS IN THE SOUTHEASTWHILE THE MID-ATLANTIC STATES PREPARE FOR HEAVY SNOW. THE MASSIVEAREA OF PRECIPITATION OVER THE SOUTHEASTERN U.S. IS RAPIDLY MAKINGITS WAY TOWARDS THE MID-ATLANTIC STATES. THIS STORM HAS ALREADYDROPPED MORE THAN 3 INCHES OF RAIN IN SEVERAL STATES ALONG THEGULF COAST. AS THE EVENING WEARS ON AND TEMPERATURES DROP BELOWFREEZING THE PREDOMINANT PRECIPITATION TYPE WILL CHANGE FROM RAINTO SNOW. THE HEAVIEST SNOWFALL AMOUNTS ARE EXPECTED IN PORTIONS OFVIRGINIA...WEST VIRGINIA...NORTH CAROLINA AND KENTUCKY.THE LOW PRESSURE SYSTEM THAT IS THE ROOT OF THIS STRONG SYSTEMWILL CONTINUE TO DEEPEN AS IT LIFTS NORTHWARD. AN EXTREMELYPOWERFUL PACKAGE OF UPPER-LEVEL ENERGY IS SUPPORTING THIS SYSTEM.AS THE LOW STRENGTHENS MOISTURE FROM THE ATLANTIC WILL BE WRAPPEDAROUND TO THE NORTH AND WEST OF THE LOW...PROVIDING A GENEROUSAMOUNT OF MOISTURE OVER THE MID-ATLANTIC AND TENNESSEE VALLEY. NEWYORK CITY...PHILADELPHIA...BALTIMORE AND WASHINGTON D.C. ARE AMONGTHE MAJOR CITIES THE HEAVY SNOW WILL IMPACT. SNOW DEPTH IN SOMEAREAS WILL BE WELL OVER A FOOT...WITH EVEN LARGER AMOUNTS IN THEHIGHER TERRAIN OF THE APPALACHIANS. THE BULK OF THE STORM WILL BEWINDING DOWN EARLY SUNDAY.A WEAK FRONTAL SYSTEM IS ENTERING THE PACIFIC NORTH WEST THISAFTERNOON. LIGHT RAIN AND SNOW WILL BE THE NORM WITH THIS SYSTEM.AREAS OF HIGHER TERRAIN IN THE NORTHERN ROCKIES MAY RECEIVEMODERATE SNOWFALL. PRECIPITATION WILL CONTINUE ACROSS THENORTHWEST THROUGH THE WEEKEND. COLLINS
