Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 447 PM EDT Thu Jul 27 2017 Valid 00Z Fri Jul 28 2017 - 00Z Sun Jul 30 2017 ...Unusual July coastal storm expected to spread soaking rains and gusty winds across the Mid-Atlantic Friday and Saturday... ...A threat of flash flooding continues for parts of Desert Southwest, central/southern Rockies into central High Plains... The stage is set for a rather unusual storm to form over the Mid-Atlantic Friday into Saturday. This storm, reminiscence of a nor'easter during the cool seasons rather than in mid-summer, is currently at its formative stage across the mid-Mississippi Valley into Ohio Valley as a couple of low pressure waves ride along a cold front. As the cool air mass behind the cold front continues to filter into the northern U.S., an upper-level trough is forecast to form over the Great Lakes and interact with the low pressure waves along the cold front. This will lead to the intensification of a low pressure system over the mid-Atlantic region late Friday into Saturday. Showers and thunderstorms currently over the mid-Mississippi and Ohio Valleys are expected to spread rapidly eastward across the Appalachians Friday morning, and overspreading the Mid-Atlantic by Friday afternoon. The storm is forecast to intensify most rapidly Friday night and early Saturday as it moves across the Mid-Atlantic states. Rain is expected to become heavy Friday night along with strong gusty winds, especially along the coast. Potential exists for 2 to as much as 5 inches of rain to fall from the central Appalachains eastward into the northern Mid-Atlantic coast through Saturday. The storm is forecast to reach an intensity rarely attained in late July along the East Coast outside of tropical storms and hurricanes. Heavy rain and strong winds are expected to lead to areas of flash flooding across the Mid-Atlantic, especially near the coast, as the low pressure center could linger just off the coast before it slowly weakens by Saturday evening. Parts of the Desert Southwest, Four Corners, central/southern Rockies and into the central High Plains will also have scattered showers and thunderstorms as monsoonal moisture interacts with a weak frontal boundary over the western High Plains. It appears that eastern Colorado and New Mexico will get the greatest rainfall totals, with a few instances of flash flooding possible. Across the southern Rockies, much of the initial thunderstorm activity should congregate across the local mountain ranges before migrating toward the valley floors and the central High Plains. Much of the heat over south-central U.S. today should gradually abate as the aforementioned cold front edges southward towards the Gulf Coast. This will confine much of the showers and thunderstorms along the Gulf Coast through Saturday. Elsewhere, the Pacific Northwest should remain dry with near normal temperatures. Kong/Hamrick Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php