After a relatively quiet weather period over the Midwest for the past several days, things are looking to cook back up in the area with a marginal risk of severe weather across the entire state today, an enhanced risk over northeast Iowa tomorrow, and another enhanced risk of severe weather over eastern Iowa tomorrow. Hot temperatures can also be expected through Monday with heat indices reaching nearly 110° in some areas in southern Iowa Monday.

It will be another mild day across the state with temperatures up to the upper 70s and low 80s in the northeast to the low 90s in the southwest. The bigger factor in this will be the northward Gulf of Mexico moisture flow and other meteorological features leading to dew points in the mid-to-upper 70s and precipitable water levels in the 1.5″ to 2″+ range across southern Iowa. In turn, a very muggy day will be seen for many with heat indices approaching 100° in several spots. This will lead to an extremely unstable atmosphere that will ultimately be capped, which is why only a marginal risk of severe weather has been posted for today.

At this point you’re likely asking, with that much instability: wouldn’t this be a very good severe weather day? Well, not quite. Severe weather is very complex and requires several different features present to happen, and the four basic ones would be instability, moisture, shear, and lift. Well, we have the vast majority of those, except for shear – which will be fairly weak. There is a chance that the instability alone will be able to make up for the lack of shear, however there is also a capping inversion in place, which will make it harder for storms to fire and make the probability of overcoming the cap and making up for the lack of shear rather low. Nonetheless, any storms that do have the capabilities of firing will be in a very good environment for large hail and damaging winds.

There may also be a pair of clusters that affect the area: one the in the morning to early afternoon in eastern Iowa, which may have an isolated strong-to-severe storm as the atmosphere destabilizes and another late in the night in southern Iowa with a locally damaging wind gust or large hail event as the instability winds down.

Yet another day of severe weather is expected Sunday, especially across northern Iowa. Temperatures will be hotter than today with highs in the low-to-mid 90s for many with heat indices in the 100s (approaching 110° in Sioux City!). This, again, will create a very muggy day across the area with a lot of instability available to tap into. A warm front will be draped across the northern most portion of the state and will likely serve as the conveyor belt for storms that roll through.

Storms will begin forming in the northern Plains and initially have a very large hail, damaging wind, and isolated tornado threat before they propagate eastward. It should transition to an MCS further down the line and pose a damaging wind threat primarily, but with all MCS’s, an isolated tornado will also be possible along the line, but the best chance for this will be during the cellular stage. The majority of the state should remain capped off from any storm development, even with additional extreme instability.

Another enhanced threat of severe weather will exist Monday with temperatures in the 90s for just about the entire state with a few spots approaching 100°, mainly in southern Iowa. I would not be surprised to see Heat Advisories pop up over the next couple of days as the 105° feels like temperature will be met in several spots. It will be another extremely unstable, yet capped day across the state. This will be one of several wildcards that puts more uncertainty into our forecast.

One issue that will exist will be the lack of forcing available. There will be a surface trough moving through the area in the afternoon that may help matters, but the timing of this is up in the air. Shear is also weak, so any storms that are able to break the cap later in the day will be linear in nature. It’s also worth noting that two of the weather models we look at both have dew points in the low 80s, which is probably overdone and unlike the climatology for Iowa at this time of year. This creates a bias for the instability and overclocks a lot of the numbers that we look at. It is hard to get an accurate representation of numbers with this bias.

Currently, our expectations with this is that any storms that fired Sunday night will continue marching eastward across Illinois on Monday morning, all while leading way to the unstable atmosphere in the afternoon. The stage for severe weather will setup where the warm front feels like sitting. Current expectations has this just to the northwest of the Quad Cities. Storms should eventually form a mesoscale convective system and pose a threat for large hail, damaging winds, and an isolated tornado. Flash flooding is also a concern with the ample moisture available in the area. The system should move eastward and continue through the evening and overnight hours.

It is important to note that this is still three days out and a lot of things are unsure of right now. What happens today and tomorrow could have a detrimental effect on what occurs Monday, and there are a lot of meteorological variables that are still being figured out.

Stay tuned to the Iowa Weather Network for the latest information!