An arctic airmass over the northern Plains will slide southeast through our area tonight and Tuesday. This cold ridge of high pressure 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 Thursday and Thursday night depending on the depth of the cold air. (Please visit http://weather.gov/lsx for more information.)