Active weather in the Midwest will spread into the Northeast on Monday as the low pressure system in the Upper Mississippi Valley treks northeastward through the Upper Great Lakes.Moisture will interact with an associated warm front that will lift across the Ohio Valley, Lower Great Lakes and the southern Northeast. This duo will spark areas of rain, sleet, snow and scattered thunderstorms from the Midwest through the southern New England Coast. Meanwhile, an associate cold front will trek from the Central Plains and the Southwest to the Mississippi Valley with more stormy weather. Snow showers will develop in the Central Rockies, while areas of showers, heavy rain and thunderstorms develop from the Central and Southern Plains through the Ozarks and Ohio Valley. Storms from the Lower Great Lakes and the Gulf Coast States through the Ohio Valley and the Appalachians may turn severe with severe hail and possible tornadoes through the afternoon.Ahead of this front, moist flow and strong high pressure will provide warm weather to the eastern third of the nation. Highs in the 70s and possibly 80s are expected in parts of the Eastern Seaboard.In the West, increased moist flow and approaching front from the Pacific will bring more rain and high elevation snow to the Pacific Northwest.Temperatures in the Lower 48 states Sunday ranged from a morning low of 6 degrees at Mt. Washington, N.H., to a high of 100 degrees at Childress, Texas.