Weather across America

(NATIONAL) More unsettled weather expected to bring beneficial precipitation across the Pacific Northwest and the Northern Rockies, mixed light rain and snow will brush the northern borders of the Northern Plains to the interior Northeast, fair and mild weather expected to continue from the southwest to the east, and cool Pacific air arrives over the West.

Unsettled weather is forecast to move across the Pacific Northwest into the northern Rockies through Tuesday with the arrival of a couple more upper-level troughs from the eastern Pacific.  The leading shortwave will spread rain as far south as northern California by Sunday night while locally heavy rain is forecast to reach coastal southwestern Oregon into northwestern California where a marginal risk of flash flooding is in place.  

From Monday through Tuesday morning, the heaviest precipitation is forecast to reach farther inland near/along the Cascades as well as farther south along the Sierra Nevada where wet snow can be expected close to the highest peaks. This moisture surge will then penetrate inland, keeping a good chance of light to moderate rain showers at low elevations and snow over elevated terrain across the Intermountain West and the northern Rockies through Tuesday.

Meanwhile, shortwave energy ejecting out of the western U.S. will lead to the formation of a pair of clipper low pressure systems farther downstream. The first system will track quickly east across the northern Plains Sunday night and across the Great Lakes on Monday.  A round of mixed light rain and snow can be expected near the northern borders of the northern Plains to the upper Great Lakes through Monday night.  

On the other side of the intensifying system, some wintry precipitation is forecast to reach northern New England Monday night ahead of a warm front before milder air from the south changes the precipitation to rain during the day on Tuesday. In the meantime, the second clipper system developing on the lee side of the northern Rockies will spread the next round of mixed rain and snow once again near the northern border of the northern Plains Monday night into Tuesday. Rain is forecast farther south from the Great Lakes on Monday to much of interior New England on Tuesday. 

As the unsettled weather continues over the Pacific Northwest, fair and mild weather will continue from the southwestern U.S. through the central and southern Plains as well as much of the eastern U.S. for the next few days thanks to a relatively zonal upper-level flow across the southern tier of the country.  

In fact, there is an increasing chance of record high temperatures especially over the central to southern High Plains by Tuesday afternoon, and as far east as the interior Southeast.  By Tuesday, a cold air mass will be ushered into the western U.S. following the passage of the last piece of shortwave energy behind a strong cold front.