The nation's weather

June 20, 2011 - 5:43 AM

More active weather is expected in the nation Monday as a low pressure system forms over the Central Plains.

This system will spread plenty of warm moisture from the Gulf of Mexico northward as it lifts northeastward into the Upper Midwest. Expect numerous showers, periods of heavy rain and thunderstorms to develop ahead of an associated cold front moving through the Central Plains and an associated warm front lifting across the Mid-Mississippi and Ohio Valleys through the day. Areas from eastern Nebraska, southeastern South Dakota, southern Minnesota and much of Iowa will see a moderate risk of severe weather development Monday. Storms in the morning may be accompanied by hail. Strong daytime heating will enhance instability near the aforementioned frontal boundaries later in the day, creating chances of large hail, damaging wind gusts and tornadoes. The threat of severe weather is expected to continue overnight with chances of damaging winds and large hail.

Meanwhile, waves of energy and moisture will spark additional showers and thunderstorms from parts of the Central and Southern Plains through the Ohio and Tennessee Valleys and into the Mid-Atlantic. There is a slight risk of severe weather development over the Central and Southern Plains across the Mid-Mississippi and Ohio Valleys into the Southern Appalachians and the Carolinas. The main threats with these storms will be damaging wind gusts and hail.

Elsewhere in the East, hot and humid weather conditions will remain in place over the Deep South. A cooling trend is expected to begin Tuesday.

In the West, precipitation will continue in the Northern and Central Rockies, while temperatures in the Intermountain West begin to warm Monday. Meanwhile, expect Red Flag Warnings to persist in the Southwest as strong winds, single digit relative humidity levels and near record breaking daytime temperatures create critical to extremely critical fire weather conditions.

Temperatures in the Lower 48 states Sunday ranged from a morning low of -22 degrees at Cottonwood Pass, Colo., to a high of 109 degrees at Pecos, Texas.