An active pattern is expected in the eastern half of the country through the weekend.

First, underneath an upper ridge that has been bringing very warm temperatures to the central and eastern US a trough will continue to move through the Southeast and Mid- Atlantic today and Saturday, then makes it off shore by Sunday. This feature will continue to produce scattered showers and storms in the Southeast and Mid-Atlantic today and tonight, Mid-Atlantic on Saturday, and linger isolated chances in parts of New England on Sunday.

Next, further west a large scale upper trough moves into the Plains Saturday and into the Midwest on Sunday. A cold front will track through the Plains today and continue east through the weekend. Scattered shower and storm activity is expected along and just ahead of this front with a chance of a few of these storms becoming severe with the better chances in eastern NE, and central/eastern KS tonight with less chances into western IA and southwest MN, and on Saturday the threat moves east mainly into the Mid and Lower MS River Valley with less chances into eastern IA, northern IL and parts of WI. By late Saturday night/early Sunday a strong surface low is expected to develop in the east IA/ northern IL/ southern WI region and this system could pull down enough cold air for a changeover or mix with snow in parts of IA, MN and WI with the potential for small snow accumulations. 

Finally, the next large scale trough builds into the Northwest for the second half of the weekend and will bring increasing precipitation chances to western OR, western WA and northern CA throughout Sunday.