Monday

This morning, a long line of thunderstorms is currently moving east-to-northeast across the state. This is behind a cold front extending from Canada to a low pressure center in southeastern Nebraska. This will continue pushing to the east or southeast very slowly this morning. It is a bit uncertain how long this system will remain in the state. This is the biggest wild card when looking at the forecast for this afternoon as this will impact how much instability can get into the area. By midday, diurnally-built instability and low-level convergence will begin having firing storms in the early afternoon across southern Iowa. With an environment characterized by very strong instability, any storms that do have the ability to develop will be in a very unstable environment. There will also be enough “lift” in the atmosphere as a pair of vorticity complexes relaxes near the area.

The only concern is that there is not a lot of shear in the atmosphere, which is a key component in severe storm development. This is the primary reason why there has not been an upgrade to an elevated risk. However, any storms that do have the shear to develop will be in a instability-rich atmosphere, and large hail and damaging winds will be possible. The window for severe storm development will not last long as the atmosphere becomes essentially waterclogged via the low level jet flooding in moisture. While this won’t fester severe weather, this will keep widespread showers and thunderstorms over the area for quite a while, through Tuesday morning, especially considering the atmospherically-deep moisture that is available over the area. The instability will drop off after sunset, however, which won’t make things too heavy or strong – just widespread light-to-moderate precipitation.

Tuesday

Attention then turns to the elevated risk of severe weather that is sitting over basically the entire state (with the exception of far northwest Iowa) tomorrow. This risk does have potential to be thwarted by leftover precipitation and cloud cover from the overnight locally. In addition, an event bigger wild card exists on where a low pressure system sets up. Some models have this being around the southeastern Nebraska/southwestern Iowa region, which would make Iowa the stage for severe weather development. If some daytime heating can kick into the area, the aerodynamic setup is definitely there to make this potentially a significant event.

Winds at the surface will be southerly, bringing warm and moist tropical air into the area, while there will be cold air aloft. A low level jet will be kicking in also at 35-45 MPH. Decent helicity and low cloud bases will also exist. This type of environment typically leads to a very large hail and tornado threat associated with discrete cells that form. The current idea, if clouds can clear (which is still up in the air), that several discrete cells will form across western Iowa and pose the threats mentioned. This would likely turn into a multi-cellular line as it reaches I-35 and create one or more bowing segments.

It’s important to note that there are several uncertainties with this and it will have to be monitored closely throughout today and the early part of Tuesday. There are several wild cards that will have to be figured out and answered before a more confident answer can be given.

The best plan of action for now is to have your NOAA Weather Radio ready to go. Stay tuned for the latest updates!