Weather across America

(NATIONAL) Unsettled weather will expand across the West through the next couple of days with heavy mountain snows over the Four-Corners and along the Cascades, a low-pressure system will trigger an expanding area of showers and thunderstorms over the Central/Southern Plains, and unseasonably mild and mostly tranquil weather for the eastern half of the country to start the week. 

A significant change in the weather pattern is forecast for the next couple of days in the western U.S. with the simultaneous arrival of two storm systems. One system currently moving through the Southwest will spread locally heavy mountain snows (12"+) across the Four-Corners region Sunday night into Monday before emerging into the Southern Plains Monday night into Tuesday. Some light to moderate rain and a few thunderstorms are also expected for lower elevation/valley locations of the Desert Southwest and Southern Rockies. 

To the north, another system will bring mountain snow and lower elevation rains to the Pacific Northwest later Sunday and will expand into the Intermountain West on Monday, followed by the northern Rockies by Monday night. Heavy snow totals over a foot are possible for higher elevations in the regional mountain ranges here as well, especially for the Cascades. As the southern system departs into the Plains, the northern system will press southward, helping to continue higher elevation snow/lower elevation rain chances for the Great Basin, Rockies, and Southwest Tuesday. 

Mostly seasonable highs on Monday outside of the rain-cooled Desert Southwest will turn much cooler Tuesday as well. Highs will be in the 20s and 30s for the Great Basin/Rockies, 40s for the Pacific Northwest, 50s for most of California, and the low to mid-60s for the Desert Southwest. Strong, gusty winds are also expected along portions of coastal California as well as the Sierra and adjacent desert locations.

Upper-level ridging will move over the center of the country ahead of the systems in the West Monday, leading to dry and unseasonably mild conditions. High temperatures will be running 10-20 degrees above average, with highs in the 30s and 40s for the Northern Plains, 40s and 50s for the Northern High Plains and Central Plains east into the Ohio Valley, and 60s and 70s for the Southern Plains. The southern system over the West moving into the Southern High Plains late Monday into Tuesday will trigger strong, gusty winds as high as 55-65 mph. Showers will develop ahead of the system moving through the Central/Southern Plains and eventually into the Mississippi Valley. Some thunderstorms will also be possible, especially for the Southern Plains and Lower Mississippi Valley. 

A light wintry mix of snow, sleet, and a glaze of freezing rain will be possible over the Northern Plains/Upper Midwest as the northern system over the West also begins to move into the Plains Tuesday. Much colder, arctic air will begin to push southward across the region later in the day Tuesday following the passage of a cold front with temperatures plummeting into the teens and 20s. Some accumulating snowfall may begin to overspread portions of the Northern High Plains as the threat of more impactful winter weather will ramp up for the region heading into mid-week.

A low-pressure system responsible for the dreary weather for the Southeast/Mid-Atlantic and winter weather in the Appalachians will move off the East Coast early Monday. The rain and higher elevation snow is expected to taper off from west to east later Sunday as gusty winds from the north subside. Temperatures will quickly rebound across the region as most of the eastern half of the country sees unseasonably mild weather similar to the Plains. Highs on Monday and Tuesday will range between the

30s and 40s for the Interior Northeast/New England/Upper Great Lakes, the 50s and 60s for the Lower Great Lakes/Ohio Valley/Mid-Atlantic, and the 60s and 70s for the Southeast. Highs look to remain mild into the mid/late week beyond the current forecast period, especially along the East Coast. Otherwise, a weak disturbance moving through the Interior Northeast may trigger some light wintry precipitation late Monday evening into Tuesday morning.