An arctic airmass over the Eastern Plains will slide southeast into the Ohio Valley through Tuesday. This high will keep temperatures well below normal through Tuesday. There will be a brief warm-up on Wednesday...but another cold front will push through Wednesday night and another very cold high pressure system will build into the Mid-Mississippi and Ohio Valleys Thursday. Meanwhile...a storm system will develop over the Great Plains which will push warm moist air up over the shallow cold layer over Missouri and Illinois. A variety of wintry weather is possible depending on the depth of the cold air. (Please visit http://weather.gov/lsx for more information.)