"Farther east, the weather will again tend to trend much milder and wetter,
as a storm system develops over the lower Mississippi Valley region on New
Year's Eve and lifts north up across the lower Great Lakes region.
Southerly flow ahead of a low center and attendant cold front will result
in notably warmer temperatures lifting north from the Gulf Coast states
and overspreading much of the Eastern half of the nation. High
temperatures especially along and just west of the Appalachians including
the Tennessee and Ohio Valleys will be as much as 15 to 25 degrees above
normal on New Year's Eve.
With the influx of warmer air will also be a
substantial amount of moisture, and the expectation is for a rather
widespread area of heavy rainfall and embedded thunderstorms to impact the
Southern and Eastern U.S. from the lower and middle Mississippi Valley
east to the Ohio Valley and Mid-Atlantic region. Some localized runoff and
flooding concerns will be possible given rainfall amounts of as much as 1
to 3 inches with this next system, and based on this, the Weather
Prediction Center has issued a Marginal Risk of excessive rainfall. In
addition to the rainfall, there will be a localized concern for some
severe weather, especially across the Gulf Coast states, and this is where
the Storm Prediction Center has highlighted a Marginal Risk of severe
thunderstorms. The concerns for heavy rainfall and severe weather will
both need to be closely monitored over the next couple of days."
http://origin.wpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=pmdspdOh, goody.