Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 353 PM EDT Sun Apr 22 2018 Valid 00Z Mon Apr 23 2018 - 00Z Wed Apr 25 2018 ...Thunderstorms and heavy rain with possible flash flooding for the southern Appalachians and Southeast for the early part of this week... ...Accumulating snow expected over parts of the northern Rockies and northern High Plains beginning tonight... An upper level low, currently approaching the lower to middle Mississippi valley, will keep locations from the Ohio valley to the Mid-Atlantic and Southeast unsettled over the next couple of days. The greatest threat from this storm system will be heavy rain, with a broad 1 to 3 inches expected through Tuesday evening from the Tennessee valley into the southern Mid-Atlantic region. Higher rainfall totals of 3 to 6 inches are expected for portions of the southern Appalachians where flood watches have been issued through Tuesday morning. Locally heavy rainfall with this storm system could bring flash flooding to a broad section the Southeast and Mid-Atlantic through Tuesday night. Moisture from the Gulf of Mexico and western Atlantic will converge upon the Southeast late tonight into Monday with moderately strong southeasterly winds ahead of the upper low allowing for upslope enhancement to precipitation totals. Gusty winds will also be a factor across the Southeast, especially into the mountainous terrain tonight through Monday, with gusts possibly peaking in the 50-60 mph on Monday. A high wind warning is in effect for portions of the southern Appalachians through Monday night with downed trees and power lines a possibility as a result of the strong winds. The other significant weather system to impact the lower 48 through the early week will reach the northern Rockies tonight. Rain and higher elevation snow will develop tonight across Idaho into Montana and Wyoming near a frontal boundary and upper level disturbance. As the system moves east early Monday, colder air will filter in allowing a changeover from rain to snow for many lower elevation locations. The heaviest snowfall accumulations, 4-8+ inches, will be focused across the higher terrain of the Absaroka and Big Horn Mountains, but light to locally moderate snowfall accumulations are also expected eastward along the Montana/Wyoming border into the High Plains and Black Hills. Cool and rainy conditions will reach parts of the central and northern Plains on Tuesday. High pressure associated with colder temperatures will also filter in behind the storm system's cold front, bringing high temperatures into the 10-20 degree below average range for Montana/Wyoming on Monday and into the central Plains for Tuesday. Otto Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php