National Weather Service Chicago/Romeoville IL
2:54 AM Monday December 18.
waves are provided as a range of significant wave heights, which is the average of the highest 1/3 of the wave, along with the average height of the highest 10% of the waves which will occasionally be encountered. synopsis, low pressure of 29.1 inches over northern manitoba will move east across hudson bay tuesday morning with a cold front trailing well south from the low moving across lake michigan by midday tuesday. a ridge of high pressure averaging 30.3 inches over the northern plains tuesday morning will move east and be centered over the great lakes by wednesday afternoon. meanwhile, wednesday afternoon, new low pressure of 29.5 inches will develop over the central high plains. this low will track east-northeast to northern illinois by friday morning, then deepen to 29.3 inches as it moves more slowly northeast to southern quebec by saturday morning.