Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 238 AM EST Wed Dec 16 2020 Valid 12Z Wed Dec 16 2020 - 12Z Fri Dec 18 2020 ...Major winter storm to bring a plethora of impacts across the Mid-Atlantic and Northeast between today and Thursday... ...More unsettled weather expected across the Northwest over the next couple of days... The biggest weather story over the next few days will undoubtedly be from a major winter storm that is set to bring an overabundance of hazards from the Mid-Atlantic to the Northeast. The driving factors behind this storm include a deep upper-level trough currently swinging across the Mid-South, an area of low pressure developing off the Southeast coast, and a strong arctic high pressure system located over southern Quebec, Canada. These ingredients will result in an expanding area of snow to overspread the Ohio Valley, central Appalachians, and northern Mid-Atlantic today. Between the snow in the north and the rain in the south, a wintry mix is forecast to stretch across the southern Appalachians and the interior Mid-Atlantic roughly along the I-95 corridor. Freezing rain is the main concern across this region, as upwards of a quarter inch of ice accretion is possible. This could lead to scattered tree damage and power outages. As the precipitation shield advances north throughout the day, heavy snow will overtake areas northwest of I-95 in the Mid-Atlantic. This means major cities, such as Washington D.C. and Philadelphia, will likely see a wintry mix and potentially plain rain for areas just to the southeast. Further north and east, heavy snow will also encroach upon much of the Northeast and southern New England this evening, including New York City and Boston. As the storm strengthens off the New Jersey coastline tonight, strong northeast winds will likely lead to coastal flooding from Delaware to Cape Cod. Flooding from heavy rain will also be possible across portions of the Mid-Atlantic where temperatures are too warm for wintry precipitation. In case that wasn't enough, severe thunderstorms could bring damaging winds and isolated tornadoes across the Outer Banks in eastern North Carolina this afternoon. The heaviest snowfall amounts from this system are currently forecast across central Pennsylvania, where as much as two feet of snow is possible. This will likely lead to very dangerous, if not impossible, travel conditions and isolated power outages. Many locations from eastern West Virginia to far southern Maine are forecast to see a foot of snowfall accumulation. In certain areas, this would be more snow in one event than was seen all of last winter. Snowfall amounts are expected to drop off dramatically to the south and east as sleet and rain are expected to mix in. There is still some uncertainty regarding exact alignment of the rain/snow line, as substantially different weather conditions could be found just a few miles apart at times. Be sure to check your local forecast for the latest updates and more specific details. Meanwhile, the Pacific Northwest will see their own unsettled weather through the next couple of days as a potent low pressure system crosses the region today and Thursday. Rainfall amounts of 1 to 3 inches are likely during this time frame along the immediate coastline from northern California to Washington. Across the Cascade and Sierra Mountains, as well as and higher elevations of the Intermountain West, 1 to 2 feet of snow could fall. Snell Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php