Weather across America

(NATIONAL) Moderate to heavy coastal rain and mountain snow expected across the western mountains, above normal temperatures continue in the East, and cooler air expands across the West.

A deep upper-level low will drive the hazardous weather in the West while an upper ridge amplifies as it shifts from the central U.S. into the East. A series of low pressure systems will glide down the West coast as they spread anomalous Pacific moisture over the region. Moderate to heavy rainfall is likely along the coast and in lower lying areas in the interior of the West. The rainfall may pose a particular threat to parts of southern California on Tuesday, where a slight risk of flash flooding is in effect. 

Scattered to isolated thunderstorms are also possible over parts of California over the next couple of days. Moderate to heavy snowfall already underway in the Cascades and Northern Rockies is expected to spread into the Sierra and Central Rockies tonight. Light to moderate snow may also impact portions of central/northern Montana. Between 2-4 feet of snow is likely to fall over the Sierra through Tuesday and 1-2 feet of snow possible in the Northern Plains with locally higher amounts possible during this period.

Cold air will filter in across the West as the upper low and associated surface cold fronts swing through the region. High temperature anomalies ranging between 15-25 degrees below average are likely to be realized in the West through Tuesday with the greatest departures from normal occurring over Montana and the Cascades/Rockies. An upper ridge will allow warm southerly air to flow into the eastern U.S. over the next day or so before a moderating trend brings seasonal fall temperatures back by midweek. 

A tightening pressure gradient, dry conditions and above normal temperatures will pose elevated fire weather concerns over portions of the Northern Plains/Upper Midwest through Monday. Some light thunderstorm activity may develop over parts of the ArkLaTex on Monday before the approaching western low-pressure system focuses more rain and thunderstorms over the Upper Midwest by Tuesday evening.