Weather across America

(NATIONAL) Above-normal temperatures to spread from the west into the central U.S., more heavy rain and flooding possible for parts of the southern Plains and mid-Mississippi Valley, and a heavy rainfall threat moving east into the lower Ohio and Tennessee Valleys.

Above-normal temperatures are forecast to persist along the West Coast through the period while extending across the Intermountain West and into the Rockies early this week. For many locations, daytime temperatures will reach 10-20 degrees above normal on both Monday and Tuesday. A

weak area of low pressure in the upper levels of the atmosphere may provide some relief and an increasing chance for showers and thunderstorms. But high temperatures may once again exceed their daily records for parts of the Pacific Northwest, including the Seattle and Portland metro regions, on Monday. 

Energy in the upper levels of the atmosphere interacting with a moist airmass will continue to produce areas of showers and thunderstorms through Sunday evening into Monday across the central and southern Plains and mid-Mississippi Valley. Some of these storms may become strong to severe, producing large hail damaging winds, as well as heavy to excessive rainfall.

High pressure to the north will support above-normal temperatures across the northern Plains and Upper Midwest on Monday, that will extend farther south on Tuesday.

By early Tuesday, an area of low pressure is expected to strengthen and move east through the Tennessee and lower Ohio Valley regions. While drier conditions are expected for much of the central Plains and mid-Mississippi Valley, the threat for heavy rain is likely to increase across parts of the Tennessee and lower Ohio Valleys into the southern Appalachians on Tuesday. 

It will be another cold morning on Monday across the Great Lakes and Northeast, with frost advisories in effect for parts of northern Lower Michigan, Upstate New York, northern Pennsylvania, Vermont, and New Hampshire. A Freeze Warning is effect for parts of northern Lower Michigan as well. Temperatures are expected to rebound before a strong cold front drops into the region on Tuesday.