...Temperatures will be 10 to near 20 degrees below average from the Great Lakes/Ohio Valley to parts of the Northeast/Mid-Atlantic...
...Temperatures will be 10 to 20 degrees above average for the Northern Plains/Central High Plains to the Northern Rockies/Great Basin...
A closed upper-level low over the Great Lakes will slowly weaken as parts of the energy lifts northward into Eastern Canada, while rest of the energy moves off the Mid-Atlantic Coast by Tuesday.
Underneath the cold pool aloft, scattered wet snow will develop over parts of the Great Lakes through late Monday morning. As the energy moves eastward, scattered rain will develop over parts of the Lower Great Lakes and parts of the Central Appalachians by Monday evening. The associated front will slowly move off the Florida peninsula by Monday evening, producing scattered showers and
thunderstorms over parts of the southern tip of Florida.
High pressure over Lower Mississippi Valley will aid in streaming moisture into parts of the Lower Rio Grande Valley producing showers and thunderstorms over parts of the area through Tuesday. In addition, diurnal heating will trigger scattered showers and thunderstorms during the late afternoon and early evening on Sunday and Monday over parts of the Northern/Central Rockies.
Meanwhile, a front over the Northern Rockies/Pacific Northwest will move eastward to the Northern Plains/Great Basin by Tuesday morning. Weak onshore flow will produce scattered rain over parts of the higher elevations of the Pacific Northwest through Tuesday. The system will trigger showers and thunderstorms over parts of the Northern Rockies/Northern Plains Monday evening. As the associated warm front moves eastward, moisture will pool along the boundary, as the air mass is lifted, condensation will occur producing light rain over parts of the Upper Mississippi Valley/Upper Great Lakes from Monday afternoon into Tuesday morning.