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Scattered non-severe thunderstorms are ongoing across southern and southwestern Iowa and are expected to continue through sunset.
Dangerous heat continues today before relatively cool temperatures set in tomorrow and Wednesday.
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Revised in 4 passages since the 2:46 PM discussion. See every revision.
Short Term
Somewhat scattered non-severe thunderstorms are ongoing across parts of southern Iowa. This activity is expected to continue through sunset. Mesoanalysis shows plenty of surface-based storm energy (upwards of 5,000 J/kg), healthy lapse rates from 6.5 to 7 degC/km, and bulk shear values of around 30kts. Storms today could have some gusty winds with them, and some more impressive storms have been tall enough to potentially produce some small hail. Considering the lack of any significant changes to the environment over the next few hours, this trend is expected to continue. The limiting factor with convection being more widespread is forcing, as the boundary these storms are forming on is very weak. Behind this boundary, dewpoints are expected to fall with the most drastic decreases being across northwestern Iowa. Dewpoints will fall into the 60s and low 70s instead of being in the upper 70s or even low 80s. In turn, this will bring some (relative) relief from the extreme heat to northern Iowa today before more widespread relief comes tomorrow.
As the aforementioned boundary makes it through Iowa, dewpoints will be limited to the low 70s tomorrow and temperatures will be in the mid to upper 80s. As a result, heat indices will top out around 90 which signals the end of heat headlines for now. Lows overnight will still be pretty warm, however, in the upper 60s to mid 70s. With all of this in mind, tomorrow looks to be dry with the lower dewpoints leading to a lack of instability, strong capping in the low levels, and little to no forcing mechanisms available. While daytime highs continue to not be as extreme, overnight lows will still be fairly warm, staying in the mid/upper 60s and low 70s.
Long Term
Warm and humid conditions continue through Friday before a pattern change starts to take place. The 500mb ridge that Iowa sits on the periphery on begins to shrink and move to the west. Temperatures through most of the long-term will be cooler, with highs generally in the 80s and overnight lows falling into the 60s across much of the state. The long term looks to be fairly dry as well. There are some lower thunderstorm chances Wednesday night into Thursday as a shortwave is expected to ride overtop of the ridge. Most of the activity should be out west in Nebraska. The placement of the shortwave as it moves through will be better assessed tomorrow and Wednesday. Thursday night, a low develops over the Dakotas and will move to the east. This low will drive higher shower and thunderstorm chances as it moves through, bringing with it a cold front, leading to much lower temperatures than we've seen to start the weekend.
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