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A plume of late season heat and humidity is aimed at the central Midwest. In terms of sensible weather it means three things, we'll be either steamy, stormy, or in some cases both.

As expected, the region is now positioned near the northern periphery of the heat dome. The door is opened to hot sultry conditions right on through the week. The strength of the heat will be determined by the position of the thermal ridge and associated low level jet. The next few days models indicate the best support for MCS development and associated storm clusters is just north of my area, near the Minnesota border and off towards the Great Lakes where a capping inversion is less likely. Positioned on the ring of fire, that's the area that's under the gun for repeated thunderstorm chances with strong storms and locally heavy rain.


From a distance, the big picture seems clear without a pair of glasses. However, you put on the spectacles and the picture reveals some details that make it far more mysterious and challenging to forecast for the remainder of the week. Those devilish details are cold pools and outflow boundaries, which depending on their strength have the ability to bleed into the area, particularly during the overnight and early morning hours. That could bring storms further south than currently indicated, especially vulnerable would be my northern counties. Obviously that would lead to a wetter solution than is currently one the table.

Additionally, if storms do get further into the thermal ridge, the associated cold pools and debris clouds would hinder our ability to warm to the toasty levels some models are depicting. Such a scenario can really cause havoc with temperatures and result in unwanted busts.


At least for Tuesday, I will cautiously lean toward the drier solutions most models are depicting. Assuming we get the necessary capping and sunshine, I expect highs in the range of 90-95 with dew points 69-73. That will amp the heat index towards advisory levels around 100 degrees and accordingly the NWS has posted a heat advisory from noon until 8 PM.

Temperatures thereafter are contingent on what happens with storms Wednesday night through Friday. Unfortunately models are not good at determining mesoscale details in the set-up we'll be facing. That leaves me with low confidence as to whether or not the heat can remain intact at such a high levels beyond Tuesday. Some signals indicate the need for additional heat advisories (especially over the south). Others show convective debris and cooler solutions. I could see either scenario playing out but I'm leaning more towards highs in the upper 80s to near 90...several degrees cooler. It's going to be a day to day challenge to figure temperatures out.


By now you may have noticed that much of the problem with forecasting temperatures is tied to precipitation. (Will we see it or not). I've already stated I don't look for much Tuesday. If it does happen it's probably going to be across the far north, particularly around HWY 20 towards the Minnesota border.

Tuesday night or early Wednesday we have another chance and then models go off in all sorts of directions. With plenty of instability, potential outflow boundaries, and the active storm track just north, there's opportunity just about any day Wednesday through Sunday. However, picking a specific day or time is impossible and once again leads to low confidence and a broad brush approach with chances 30-50 percent throughout the period. Just know it can happen with the understanding there will be many dry hours, especially during the day.

Here's a sampling of what models are showing for total rainfall Tuesday night through Friday morning. Notice the emphasis is focused on northern Iowa, Minnesota, and Wisconsin, and maybe a bit of NW Illinois.



The WPC (Weather Prediction Center) BLEND

Notice the CAMS (convective allowing models) indicating more substantial rains further south...for what it's worth!




I think the bottom line in the big picture is the fact this is some tough forecasting that relies on complex factors that can't be seen in the large scale grids at this point in time. We are going to need to take it one day at a time with a nod to warm humid conditions into the weekend with at least small to moderate rain chances daily. That's the best I can do for now as I'm stuck in the middle, along with the rest of you. Roll weather...TS

PS The Cedar Rapids airport picked up 1.12" of rain early Monday. I believe that is the first time this year that 1 inch of rain fell in a 24 hour period. That is incredibly tough to do with the type of weather we experience here in the Midwest. A big thumbs up to CR for breaking that streak.