Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 316 AM EDT Thu Apr 06 2017 Valid 12Z Thu Apr 06 2017 - 12Z Sat Apr 08 2017 ...Severe thunderstorms possible across portions of the Mid-Atlantic... ...Heavy rain possible for portions of the northern Mid-Atlantic and Northeast... ...Rain and snow expected to spread across much of the western U.S. through Saturday... A deepening low pressure system will move northeastward from the Ohio valley to the lower Great Lakes today and tonight. A cold front ahead of the system will sweep eastward across the Mid-Atlantic states, bringing potentially heavy rainfall as well as severe thunderstorms. Please refer to products issued by the Storm Prediction Center for further details on the severe weather threat. Farther north, an occluded frontal system along with a plume of moisture and from farther south will bring widespread rain and a few thunderstorms to the Northeast. Rain is expected to persist across much of the Northeast through tonight and into Friday morning as the low pressure system lingers overhead. Rainfall amounts of 1 to 2 inches are possible across areas from the northern Mid-Atlantic to the Northeast. These heavy rains could produce result in flooding issues for some areas. Colder air will wrap around the western side of the low pressure system Thursday night into Friday, with rain mixing with or changing to snow across the lower Great Lakes and along the spine of the Appalachians. This mixture of rain and snow is forecast to gradually taper off through the day on Friday, but scattered rain or snow showers could persist into Friday evening across portions of the central/northern Appalachians. Much cooler temperatures will overspread the eastern third of the nation in the wake of this system, with high temperatures today and Friday forecast to be 10 to 15 degrees below average for many areas. Temperatures will begin to moderate some by Saturday, but will remain below average for many areas. A pattern change is in store for the western U.S. over the next couple days, with a return to wet and stormy conditions expected. A weak frontal system will bring rain and high elevation snows to areas from northern California to the Pacific Northwest and the northern Intermountain West early today. A more substantial system will approach the West Coast late today, however, bringing a plume of deep Pacific moisture, and spreading widespread rain and mountain snow across much of the region tonight and Friday. By Friday night, snow levels will lower across the West as an upper-level trough amplifies overhead. Rain is expected to change to snow Friday night across much of the interior West, with snow levels lowering further in the Cascades, Sierras, and coastal ranges. Heavy snow will be possible at some of the higher elevations. Also by Friday night into Saturday, another wave of low pressure is forecast to approach central California, bringing a renewed round of moisture and precipitation to the region. Ryan Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php