Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 357 AM EDT Thu Mar 12 2020 Valid 12Z Thu Mar 12 2020 - 12Z Sat Mar 14 2020 ...A Slight Risk of excessive rainfall is in place over parts of Southern California and Arizona on Thursday into Friday morning... ...Heavy snow over parts of the Northwest, the Rockies, and Central High Plains on Friday, ... ...There is an enhanced risk of severe thunderstorms Tennessee/Ohio Valleys... ...Chance for accumulating snow and rain/freezing rain in Northern New England ... An upper level trough off the coast of Southern California will continue to generate scattered showers across the Southwest. As the trough advances eastward, bands of heavy showers and thunderstorms will drench portions of Southern California, the Lower Colorado River Valley, and Central Arizona. A Slight Risk for excessive rainfall has been issued for these aforementioned areas on Thursday. Flash Flood Watches are also in effect for some of these areas through Friday. As the upper trough moves into the Four Corners region on Friday, so will its precipitation shield which will overrun a colder air-mass and lead to snow in the Rockies and Central High Plains. While exact accumulations are still subject to change, there is a good chance for greater than 6 inches of snow in portions of the Colorado Rockies, Northern New Mexico, and West-Central Nebraska. Meanwhile, in the Northwest and Northern Rockies a cold dome of Canadian High Pressure will spill frigid temperatures into these regions Friday/Saturday. A new upper trough diving south from the Northeast Pacific will be responsible for rain in the valleys and snow in the mountains of the Northwest on Friday. Winter Storm Watches have been issued for portions of Northern Montana in advance of this impending winter storm where snow totals of 6 to 12 inches of snow are possible between Friday and into Saturday night. To the east, as a surface low pressure tracks east from the Central Plains on Thursday, additional showers and thunderstorms will develop along a warm front that will extend from the Middle Mississippi Valley into the Ohio and Tennessee Valleys. Some thunderstorms will produce heavy rainfall rates and the potential exists for localized flash flooding. A Marginal Risk for excessive rainfall has been issued for portions of these regions on Thursday while a Slight Risk for severe weather extends from northeast Texas and the Middle Mississippi Valley to the Ohio and Tennessee Valleys. As a cold front swings through the Eastern U.S. on Friday, it will stall over Texas and lift north as a warm front later that evening. This will lead to another round of showers and thunderstorms in the Southern Plains Friday evening where rain may fall heavily at times. Elsewhere, portions of Northern New England may pick up several inches of snow ahead of a storm system tracking into Southeastern Canada by Friday morning. Some lake effect snow showers are also possible Friday morning over the Upper Great Lakes but accumulations will be light on average. The Nation's Heartland can expect a mild Thursday with temperature anomalies ranging between 15 to 20 degrees above normal. It will then be the East Coast's turn for spring-like temperatures come Friday. Both the Nation's Heartland and the Northeast will cool down this weekend in wake of a cold frontal passage late week. Ziegenfelder Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php