Winter Storm (Dec. 18) Update #3

Our potent winter storm is taking its' time to move through the plains, the low pressure system is currently over eastern Colorado and is expected to make its' way off of the Rockies this evening. Rapid pressure falls have been occurring over western Kansas, indicating that the low should move to the east/southeast over the next few hours. Once off the Rockies this low will rapidly move eastward over Kansas and through northern Missouri overnight, leading to heavy precipitation over parts of Iowa. The latest weather models have moved the the system just slightly north, moving the axis of heaviest snow/sleet with it. Once again both of the main weather models (NAM & GFS) are in remarkably good agreement with the movement of this system as well as precip amounts.

The heaviest freezing rain should still be south of I-80, and especially over south-central and southeast Iowa where nearly a half-inch is likely. Other areas south of I-80 should still see a quarter of an inch or more of ice. Sleet is also likely to occur over much of central Iowa between the I-80 and highway 30 corridors; total amounts between a half-inch and an inch are likely. Heavy snow throughout the night seems likely over the northern half of the state, with embedded thundersnow also possible. An axis from near Sioux City through Algona, and eastward toward LaCrosse, WI and points north/south within a few counties are likely to have the heaviest amounts of 6-10 inches. Other areas are still likely to see 4-8 inches...

More brief updates late tonight or early tomorrow are likely with reports of accumulations...