After another hot and muggy day with a severe weather risk that was ultimately kept to the north of the state, Iowa is preparing for a redo with a somewhat cleaner setup. Before we get into any of the nit and gritty details, it’s important that there is a lot of wild cards at play with how things will setup from a synoptic scale. There is an ongoing Mesoscale Convective System (MCS) across Minnesota, Wisconsin, and Iowa at this hour that continues to weaken as it moves off to the southeast. There is some general rain behind this system as well which does complicate matters. Our current idea for this morning has all precipitation out of the area by 10 a.m. this morning at the very latest (potentially earlier as the western end of this line weakens). The rain itself isn’t the concern, but instead the cloud cover.
Infrared satellite imagery has the cloud bank associated with this MCS with this extending into Central Minnesota. If this lasts too long over eastern Iowa this morning, it may have a negative effect on the severe weather later in the day. This will have to be monitored and forecasts will need to be adjusted should this happen. There are also some isolated showers and thunderstorms popping up in South Dakota, Nebraska, and areas in Iowa. This isn’t too much of a concern either as it appears to be fast moving and isn’t widespread, but again will need to be monitored. The MCS should carry on to the east of the state and leave behind outflow boundaries and cloud debris across the Ohio River Valley. This will likely be the one of the main ingredients to allow the first round of severe thunderstorms to develop in a linear fashion in the same areas. Due to the linear fashion (potentially as a bow echo), the primary threat with this will look to be damaging winds.
To the west in Iowa where storms will another set of severe thunderstorms is expected, clear skies with hot and muggy weather will prevail for the majority of the day. Highs will be in the 90s with dew point points in the 70s and even some 80s leading to heat indices in the 100s. Like yesterday, this will create an extremely unstable atmosphere with CAPE (Convective Available Potential Energy) numbers into the 7000 to 8000 j/kg range for some. This will be the primary ingredient for storm development later in the day. This very unstable environment fueled by raw instability and increasing winds in the mid-levels will allow several significant severe cells to form across eastern Iowa.
Current expectations have cells forming in the mid afternoon along a semi-discrete line from Dubuque to Centerville and eastward. All modes of severe weather will be possible – if not likely – including very large hail to the size of baseballs, damaging winds to 70 MPH, and an isolated tornado or two. This activity should continue off to the southeast before eventually lining up and forming yet another summertime mesoscale convective system or mesoscale convective vortex – potentially with a widespread and significant damaging wind threat as it continues off to the east when it interacts with past synoptic features. As with everything, this will be monitored during the day with adjustments to forecasts as needed.
Stay tuned to the Iowa Weather Network for the latest information!