Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 357 AM EDT Tue May 23 2017 Valid 12Z Tue May 23 2017 - 12Z Thu May 25 2017 ...There is a slight risk of severe thunderstorms over parts of the Southeast and the southern tip of Texas... ...Heavy rain possible over parts of the Southern Appalachians/Southern Mid-Atlantic... ...Heavy rain possible over parts of Southeast... A developing upper-level low over the Upper Mississippi Valley will slowly move southward to the Middle Mississippi and Tennessee Valleys by Wednesday evening. An old boundary extending from the Mid-Atlantic southwestward to the Central Gulf Coast will aid in developing showers and thunderstorms from the Southern Mid-Atlantic to the Central Gulf Coast that will extend from the Southern Mid-Atlantic to the Southeast by Tuesday evening. The showers and thunderstorms will generally move off the Mid-Atlantic/Southeast Coast overnight Tuesday. A front associated with the upper-level low will aid in producing rain over parts of the Upper/Middle Mississippi Valley and the Upper Great Lakes on Tuesday morning. The rain will transition into showers and thunderstorms by Tuesday afternoon will develop over parts of the Upper Great Lakes to Middle Mississippi Valley and the Southern Plains 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. Ziegenfelder Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php