Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 355 AM EDT Tue Apr 18 2017 Valid 12Z Tue Apr 18 2017 - 12Z Thu Apr 20 2017 ...Periods of rain and high-elevation snow to continue today and into Wednesday morning across the western U.S... ...Showers and thunderstorms expected from the Gulf states to the Southeast/southern Mid-Atlantic and over the Midwest/Upper Midwest... Over the next few days mostly zonal flow with a few small disturbances is expected across the country. A couple of weakening Pacific systems will send moisture across the West, spreading rain and high-elevation snow across the region today and into the Northern Plains on Wednesday. Another round is forecast for the Pacific Northwest and northern California Wednesday and beyond. The aforementioned moisture from the western U.S. will spread quickly into the Northern Plains and the Great Lakes on Wednesday in advance of a developing low pressure system in the Central Plains. Areal coverage of the rain will expand, encompassing much of the Midwest, Upper Midwest, Great Lakes, Mid-Atlantic and the Northeast by late Wednesday. o the south of the front, a line of thunderstorms may develop ahead of a dry line in the Central Plains -- the Storm Prediction has identified a slight risk for portions of the Midwest on Wednesday. Today, mild and drier conditions should return to New England and portions of the mid-Atlantic as a surface high pressure ridge builds in from southeastern Canada. Light rain will be possible on Wednesday though as easterly winds transport moisture from the Atlantic Ocean inland by Wednesday. For the Southeast, showers and thunderstorms are forecast to linger along a stationary front. Meanwhile, moisture from the Southeast will spread northward and merge with moisture arriving from the Great Lakes over the Ohio Valley and the Appalachians. By Wednesday evening, northern New England could see the arrival of some wintry precipitation. Campbell/Kong Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php