POPCORN STORMS BREAK THE HEAT...
Hit and miss storms were scattered around the area the past 24 hours. They sprung up like popcorn hitting some spots and avoiding others altogether. Thus, some received the rains they needed but far more missed out. Here's the Doppler estimates out of the Quad Cities through Wednesday evening. The dark greys and blue green colors indicate where 1/2 to more than an inch of rain came down. Morrison, Illinois picked off 1.2 inches and Lowden, Iowa was close to an inch representing some of the heavier reports I've seen. Some isolated spots probably had more than 2 in.
The front that generated the storms has taken its weak convergence and wind fields into Missouri and that will lead to a relatively cool but dry day Thursday. Despite a weak ridge of high pressure more clouds than sun is expected which should hold highs in the 70s. The EURO shows this.
That's 5 to 15 degrees cooler than we were at 1:00 PM Wednesday.
That leads us into the weekend and a pattern that has the potential to be wet at times. The driver in all of this is a digging short wave that cuts-off over Iowa. That creates a slow moving system that generates the forcing necessary for showers and storms Friday through Sunday, perhaps even Monday on some solutions.
The models are not in agreement on how this plays out but it does seem the threat for severe weather should remain to the west and south Friday. While a few scattered showers and storms could be around during the day, robust convection is likely to develop in the SW third of Iowa late Friday. This is expected to grow linear Friday evening into an MCS that will carry heavy rains of 1-3" or more wherever it decides to go as it moves southeast Friday night. Most solutions keep the activity Friday night confined to the SW half of my are (southeast Iowa and WC Illinois) and that makes sense to me. SPC shows a slight risk of severe storms Friday just to the west of my area.
Saturday as a surface low takes shape south of the upper air energy, showers and storms with it should redevelop and rotate northward into my southern counties, eventually moving north with time Saturday night and Sunday. With the system moving only slowly east, vorticity rotating around it will delivery occasional periods of rain and storms into Monday. That said, there will be plenty of dry hours. However, the precise movement of the upper air low will determine where the most significant rains will fall. With models not in sync yet there is discrepancy. One thing is for sure there is plenty of moisture for locally heavy rain where the right dynamics come together. Available water vapor Saturday night on the EURO tops 2.5" in SE Iowa. That's the type of air mass than can crank out torrential rainfall.
The 18Zz EURO shows that in the area where water vapor is maxed out Saturday night. Note the intense rain over the the area near and south of I-80 with a weak surface low near Keokuk.
Between what falls Friday night through Saturday night the18z EURO depicts some healthy rains, especially down around HWY 34 in SE Iowa where some amounts could be excessive.
The 0z EURO (6 hours later) is much further south Saturday night and you can see what a difference that makes in its rainfall output. Much more manageable.
The 18z GFS cranks out its heaviest rains near the Missouri Iowa border.
The 0z run (6 hours later) is further north in Iowa but decreases amounts further east in Illinois. You can compare above and below.
Hopefully you can see in just a six hour period how the EURO went south and the GFS went north. This illustrates how the models are really struggling with the intensity and placement of the 500mb energy, bouncing around from run to run. Until they get a handle on that forecasting rain amounts will be very challenging. Hopefully Thursday's data brings more clarity to the situation.
With all the clouds and periods of precipitation the weekend will be somewhat humid but certainly not hot. Highs are expected to stay in the 70s in most areas through Monday. Here's the average temperature departure over the next 5 days. Not looking like July!
To sum it up, high temperatures look well below normal into early next week. After Thursday, rain chances exist Friday through Monday. Overall the heaviest should remain over the south but I think even the north will end up with a good shot of at an inch or more. Substantially heavier amounts are possible across the south, especially from I-80 south. We should know more Thursday as trends become more apparent. That's all for now, roll weather...TS