DISCUSSION
Issued at 205 PM CDT Fri Jul 26 2024

It was rather impressive this morning with the storm that parked over Appanoose County. The elevated boundary, copious amounts of moisture with precipitable water values over 1.3 inches and deep warm cloud depths, moisture transport into the boundary, and hardly any low level flow kept storms nearly stationary. A CoCoRaHS observer had over 2 inches west of Centerville with a trained, reliable spotter north of Centerville recording almost 4 inches with those reports as of 7 or 8am. PoPs were held into this afternoon over our southeastern forecast area as these storms continued to fester, but have now since diminished. Along the boundary, which extends from southeastern Iowa into north central Iowa, stratus clouds were stout this morning. However, these clouds have been breaking up leaving a mixture of sunshine and clouds this afternoon in many areas of central Iowa. There does remain high level wildfire smoke over the state, which will likely linger aloft through Saturday, resulting in hazy, vibrant red and orange sunrises and sunsets barring any clouds.

All recent runs of convective allowing models (CAMs) except the RAP are showing isolated storms popping early this evening somewhere over central Iowa. This would likely be along the weakening elevated boundary, but with nebulous forcing it raises questions about whether anything will develop. With all of the uncertainty will just run with token PoPs/sub 15%, but will need to monitor. Similar to Thursday evening, if a storm does develop, brief downpours, lightning, and perhaps gusty winds given dry subcloud air would be the main concern.

For the remainder of the discussion covering Saturday through late next week, will break out by first discussing the upcoming heat wave and then storm chances. Looking at high temperatures, 850mb temperatures today should peak around 18 to 20C and result in highs mainly in the 80s over central Iowa. Saturday and Sunday may be a touch warmer than today, especially if we start the day sunnier than today. As we move into early next week, 850mb temperatures increase about 2C each day Sunday to Monday, Monday to Tuesday, and likely Tuesday to Wednesday. This should place much of central Iowa into the upper 80s to middle 90s on Wednesday with the latest National Blend of Models (NBM) showing probability of reaching or exceeding 90 degrees at 50% or higher across central Iowa. ECMWF is showing very little in the way of any extreme forecast index (EFI) or shift of tails during the upcoming heatwave meaning that while it will be hot and humid, this is not unusual for late July or early August.
Still, seasonal humidity levels are likely from this weekend into next week (dewpoints a few degrees either side of 70). Combined with the heat, this will result in heat index values well into the 90s to near 100 degrees Monday and Tuesday with more widespread heat index values above 100 degrees on Wednesday. A heat headline is certainly possible Tuesday if not Wednesday, especially considering the cumulative effect of heat on the body. The experimental HeatRisk is showing level 3/major HeatRisk (out of a max of 4) in a few places over southern Iowa Tuesday afternoon with more widespread level 3/major HeatRisk over southern Iowa into parts of central Iowa on Wednesday.

Now, onto the storm chances. While there is broad scale ridging over the region today, a shortwave beneath the ridge that is over Arkansas at midday today will drift northeastward. This shortwave and weak low level thermal lift could be the impetus for scattered storms. Some of the more convective happy models are showing this early afternoon Saturday somewhere over southern or central Iowa.
This, like tonight's chance, is quite low and have drawn in some low PoPs over southern Iowa in the afternoon with the main hazard being gusty winds, lightning, and brief downpours. The more likely period for any storms from this shortwave will be as it moves into the state Saturday night into Sunday, particularly over the eastern half of the state. Shear is lacking so not expecting more than locally heavy downpours and lightning. As this pulls into the western Great Lakes Sunday, another upstream shortwave will quickly be approaching from the Dakotas. This should bring a more widespread chance of scattered storms later Sunday evening into Monday, including the possibility of a few severe storms given the instability and higher deep layer shear values associated with this shortwave compared to Saturday night/earlier Sunday. This low severe risk is supported by the SPC day 3 marginal over much of the forecast area along with the Colorado State University's machine learning random forest outlook.

Around Wednesday, a more amplified shortwave trough will be moving through the northern states. The timing of this wave has varied from Tuesday night to Thursday, but regardless of when this comes through the region, there will be storm chances. Right now, NBM has too broad temporal and spatially the PoPs, but that is the uncertainty of this time. Severe weather may be in play with the stronger kinematic fields and instability, but where and as already mentioned when remain big question marks. CSU's machine learning random forest outlook has broad brush low probabilities throughout the middle of next week - not atypical for late July and early August.

AVIATION /00Z TAFS THROUGH 00Z SUNDAY/
Issued at 627 PM CDT Fri Jul 26 2024

Areas of MVFR ceilings may affect KMCW and KALO areas through 02z or so, with isolated showers near KDSM. The thunder potential there seems too low to mention at this point with nothing currently nearby and the likelihood diminishing into the evening. Otherwise VFR conditions are anticipated for the remainder of the period.

DMX WATCHES/WARNINGS/ADVISORIES
None.