Weather across America

(NATIONAL) A potent storm system is expected to bring a moderate risk of flash flooding and heavy mountain snow over parts of California, and a wavy front is forecast to bring some severe thunderstorms across the Southeast before intensifying rapidly into a potent nor'easter off the New England coast.

Increasingly stormy weather is expected to impact both the West and the East Coasts simultaneously over the next couple of days with the arrival of two separate but potent low-pressure systems. The widespread precipitation currently associated with a frontal system across the Pacific Northwest will gradually shift its focus southward into California over the next couple of days as a rather dynamic low-pressure system is forecast to slam onshore in California on Tuesday. Despite uncertainty on the timing of this system, the dynamics and ample moisture associated with this system is forecast to bring yet another heavy precipitation event through the next few days. Additional feet of heavy snow are again forecast for the higher elevations of the Sierra Nevada. 

Meanwhile, considerable flooding impacts are expected below 5000-foot elevation along the central California coast, San Joaquin Valley, Sacramento Valley, and southern Sierra Nevada foothills into Tuesday. In addition, heavy rain and snowmelt may lead to renewed (more widespread) flooding from Monday to Tuesday, particularly in low elevations and shallow and warming snowpack areas. Creeks and streams will continue to be vulnerable to flooding from additional rain and snowmelt. Some heavy snow can also be expected farther inland across the Intermountain West, especially central Idaho, and western Wyoming.

Meanwhile, a clipper system currently moving east through the lower Great Lakes will spread light to moderate snowfall across the Great Lakes through Sunday night before reaching interior New England on Monday. Farther south, a wavy front is forecast to bring some severe thunderstorms across the Southeast through Sunday night. 

This wave is forecast to interact with the clipper system moving across the Great Lakes and intensify rapidly into a potent nor'easter off the New England coast on Tuesday bringing heavy wet snow inland and high winds with rain/snow near the coast. Heavy snow rates (up to 2 inches per hour possible) and strong winds from this nor’easter will likely produce dangerous to near impossible travel. The heavy-wet nature of the snow could result in scattered to widespread power outages and tree damage. Confidence is increasing that some interior, higher elevation areas across the interior Northeast will receive greater than 12 inches of snow. 

In addition, the system may produce localized higher snowfall amounts for portions of the Catskills in New York, Berkshires in western Massachusetts, and southern Green Mountains in Vermont. Widespread minor coastal flooding may be possible Monday Night through Wednesday as the low pressure deepens off the coast of New England. As the precipitation moves into the Central Appalachians, pockets of rain/freezing rain will develop on Sunday. The combination of snow and ice may cause hazardous road conditions over parts of the Central Appalachians.