After a wild week of severe weather, the "fun" may not be over. There exists one more chance for storms this afternoon and tonight, but the question of whether they will be severe - or even occur at all - remains annoyingly murky.
The Storm Prediction Center has maintained a level of 'marginal' risk for severe weather for the area Saturday. An active weather pattern will allow for the ingredients for storms to pop. Let's dive into it...
As of noon Saturday, a warm front - cold front pair was approaching the Minnesota-Iowa border from the west, with a surface low pressure system having formed where they meet. Behind and along the warm front is also much more humid air that is favorable for thunderstorm development. A line of severe storms, heading due east, was developing along this front in central Iowa.
Later this afternoon, upper level winds will be favorable for the development of supercell thunderstorms as the warm front passes. Supercells are rotating thunderstorms capable of producing heavy rain, large hail, and tornadoes. The possibility of supercell development remains the primary severe threat on Saturday.
WHAT THIS MEANS
These central Iowa thunderstorms were not well forecast yesterday, and are likely eating up some of the moisture that was expected to reach the MN-IA border Saturday night. Comparing two different computer model outcomes at the same time Saturday night, one (HRRR, left) which shows the central Iowan storms and one (NAM3K, right) which does not, we can see that severe storms did not develop in the model that had the Iowa storms right. Using this, we can assume that the severe threat this evening has decreased.
However, there still remains uncertainty in how much moisture could make it to the MN-IA border, so severe storms are still possible, especially if even one thunderstorm can ramp up and fledge into a supercell.
Should storms develop tonight, there is a chance for large hail, an isolated tornado, and heavy rains. Much of the areas soil is still saturated from the past week of rain, and any significant rain could result in flooding.
We are continuing to track this storm.