A very active day is ahead on Wednesday with a chance of strong to severe thunderstorms possible across the large section of the state. The Storm Prediction Center has a enhanced risk of severe weather across the southern and southeastern counties of the state with a slight risk surrounding that covering most of the state along and south of US Hwy 20. A marginal risk covers the rest of the state. The main risks from this storm system will be from damaging straight line winds and some isolated tornadoes.
A low pressure center will be tracking into the state from the Central Plains during the day on Wednesday and is expected to track from southwest to northeast across the state. The system should move into the state during the late morning or early afternoon hours and quickly move through the state. The event window for the severe weather looks to open in our southwestern counties late morning around 11am with the threat ending in our eastern counties sometime after 7pm. Storms should grow into supercells but they are not likely to be the huge towering storms we see in the Spring and Summer. These will be low topped thunderstorms that will only range between 15-25 thousand feet. These storms will also be quick movers with storm motion indicating that the cells could move at 40-50mph or more, thus the damaging wind threat. There will be some instability but nothing compared to what we would see in the Spring or Summer. There is ample shear in the atmosphere that these cells will rotate quite easily and that could lead to some tornado development. The Storm Prediction Center indicated that this would be likely in the enhanced risk area which extends in southern Iowa into northern and Central Missouri and into Western and southwestern Illinois. A strong tornado or two was also mentioned and can’t be ruled out at this time.
It should be mentioned that these type events, although rare are not uncommon. Many in the state will remember an event that occurred in 2005 where there were numerous tornadoes across Central Iowa including one that hit Stratford north of Ames that killed a woman taking cover in her basement. There was also an event two years ago in Illinois and Indiana including a strong tornado that hit Washington IL outside of Peoria. There’s been numerous other events across the Ohio River Valley and eastern Midwest as well in November, so we’ve seen this before in the extended area.
The threat of severe weather as mentioned prior will move out of the state after sunset (generally around 7pm or so) with colder air moving in on the backside. We will see some wraparound precipitation on the backside of the low pressure center and some of this could be in the form of a rain snow mix especially in our western and northwestern counties of the state. Any accumulating snowfall will stay west of the state across central Nebraska and west and southwest from there. There is still some uncertainty when it comes to this part of the event and we’ll continue to monitor this portion carefully over the next 24 hours. Temperatures during the day on Wednesday will be in the 50s to lower 60s.
Stay tuned to the Iowa Weather Network for the latest information!
Henry Luker, Lead Forecaster
Jeff Wilcox, Assistant Lead Forecaster
Willard Sharp, Senior Forecaster
Mike Cox, Senior Forecaster