Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 409 PM EDT Mon May 22 2017 Valid 00Z Tue May 23 2017 - 00Z Thu May 25 2017 ...Unsettled weather expected to move into much of the eastern and northwestern U.S. for the next couple of days... An active weather pattern is taking shape across the U.S. over the next couple of days as the upper-level flow becomes increasingly amplified. First of all, a cool air mass behind an occluded cyclone centered north of the Great Lakes will pivot around the cyclone center and surge southward through the Plains through Wednesday. This will bring another batch of unseasonably cool air down the mid-section of the country. Daytime surface heating under upper-level cold air will promote scattered afternoon showers over the central Plains today, moving into much of the Midwest and into the upper Great Lakes on Tuesday behind the surface cold front. Ahead of the front, scattered thunderstorms can be expected over the southern Plains. Areas over western to southern Texas could see severe thunderstorms today into tomorrow. As the cool air mass continues to advance to the southeast, it will begin to interact with another frontal boundary already in place from near the Gulf Coast extending into the East Coast. The result will be the formation of a new low pressure system west of the Appalachians from Tuesday night into Wednesday. Showers and thunderstorm will then edge further eastward into much of the Ohio Valley, down into the southeastern U.S. and the Gulf Coast on Wednesday as sunshine returns through the Plains states with cool temperatures. The central Rockies will once again see the arrival of snow over the higher elevations tonight. Meanwhile, a rather compact and deep upper-level low is forecast to dip southeastward from British Columbia into the northwestern U.S. during the next few days. This will trigger the formation of a rather strong low pressure system to be centered over Alberta Wednesday morning. A surge of cool air will arrive behind a strong cold front, replacing the recent spell of mild weather over the Pacific Northwest. The highest elevations of the northern Cascades and northern Rockies could even see snow moving in on Wednesday. The front will continue to push rapidly to the south and east, triggering showers and thunderstorms during the day on Wednesday from the Sierras eastward across the Great Basin, northern Utah, Wyoming, Montana and the nearby High Plains. Kong Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php