723 FXUS63 KDMX 112345 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 645 PM CDT Wed Jun 11 2025 ...Updated for the 00z Aviation Discussion... .KEY MESSAGES... - Severe storms possible over northern Iowa this afternoon into mid- evening with main hazards being damaging wind gusts and large hail - Locally heavy rainfall tonight over northern Iowa with isolated flash flooding possible with these chances highest in urban areas or over smaller basins - Lull in storm coverage Thursday morning with additional storms in the afternoon and early evening with limited severe chances - Not a washout, but chances for storms at times into early next week with organized storms possible early next week && .DISCUSSION... Issued at 218 PM CDT Wed Jun 11 2025 A more active period of thunderstorm chances is in store over the next week largely driven by shortwave troughs being carried through the low amplitude flow. This flow can be viewed on the upper level water vapor imagery from GOES-East with one wave over the Dakotas and Nebraska and another nearing the northern Rockies. This first shortwave is reaching the state this afternoon interacting with a stationary front that is draped over far northern Iowa from just north of Sheldon to just north of Algona to north of Waterloo. This front has provided some level of convergence despite the weak surface flow with a storm along the Iowa/Minnesota border. Expectation is that additional storms will be able to form along northern Iowa this afternoon and push eastward into early this evening. Now, the weak flow does result in weaker effective shear despite the traditional deep shear values looking favorable for storm organization. Surface based CAPE values over 1500 J/kg are common south of the front already this afternoon and with the dry mid-level air, downdraft CAPE values are over 1000 J/kg. The steep low level lapse rates and still more than sufficient SBCAPE values should allow for good parcel acceleration on storm development phase that pushes past the 12kft freezing level and into the hail growth zone. This will result in a large hail threat. Further, the large downdraft CAPE values, inverted V soundings, and surface dewpoint depressions over 20 degrees F also point to the hazard of damaging wind gusts. This is shown in various convective allowing models (CAMs) such as the 12z HRRR, 0/12z ARW cores, and 12z FV3, which have small, but varying swaths of severe wind gusts (>50 knots/58 mph) over northern Iowa this afternoon into early this evening. Already have seen severe gusts up in WFO Sioux Falls service area with the one storm this afternoon. This first wave of storms will exit into northeast Iowa mid to late evening, but regeneration of additional storms is expected over Siouxland as a weak low level jet points into that region, especially late tonight into the overnight. While severe weather is not expected, locally heavy rainfall will be possible as these storms track roughly eastward following the weak 850-300mb flow along the stalled front over northern Iowa. Efficient rainfall is certainly possible given the deep warm cloud depths and precipitable water values over 1.5 inches pooling along the boundary. Rain totals of 1 to 2 inches are possible somewhere along this boundary whether in northern Iowa or southern Minnesota. A few CAMs (e.g. ARW, HRRR, FV3) also show amounts over 4 inches in varying locations, with these CAMs impacting the localized probability matched mean of the 12z HREF. Flash flood guidance (FFG) values over northern Iowa range from 1.75 to 2 inches for 1 hour, 2 to 2.5 inches for 3 hours, and 2.5 to 3 inches for 6 hour. With relative soil moisture (RSM) percentiles in the normal range (30th to 70th percentile) at the 0-10cm and 10-40cm layers, the FFG seems a bit low from an empirical sense for mid-June. So, urban areas and/or smaller basins, if the higher rainfall moves over those areas, could have isolated flash flooding. As for rivers, monthly average USGS streamflows are average and there is capacity and expectation at this point is mainly within stream bank rises. The exception would be if one of those higher QPF CAM solutions verifies and this could result in more than within stream bank rise. As we move into Thursday, there should become a minimum in coverage of any showers or storms in the morning hours that lasts into at least part of the afternoon. The second shortwave nearing the northern Rockies today looks to pass largely north of the state Thursday afternoon and night. This would keep the focus for much of the storm activity north of the state, though a few storms may move across northern Iowa mid to late afternoon into the early evening hours. These could pose an isolated hail or gusty winds threat and is currently captured in the day 2 SPC outlook. Further south outside the marginal risk area, a few storms may develop during peak heating over central Iowa. Instability may reach 1000 J/kg, but shear is weak so outside of perhaps some sub-severe hail and wind gusts as storms collapse, the activity over central Iowa looks to be more of the sub-severe variety. Depending on where the rain falls tonight (Wednesday night/early Thursday) will determine what kind of flash flooding or river flooding risk, if any, will exist later on Thursday. Low shower and storm chances will persist in parts of the state, mainly northern and eastern Iowa on Friday as shortwave energy passes north of the state and a 500mb closed low drifts northeastward over Missouri. A front may clear the state by Saturday with this weekend favoring drier, though not fully dry conditions. The machine learning/artificial intelligence (ML/AI) severe probabilities are also low or non-existent in this period. Chances for more organized storms may develop as a warm front lifts over the region and Iowa returns to the warm sector early next week. Instability and shear parameter space would point to some strong to severe storm risk with this supported in the ML/AI severe probabilities as well. && .AVIATION /00Z TAFS THROUGH 00Z FRIDAY/... Issued at 642 PM CDT Wed Jun 11 2025 Showers and storms still moving across parts of northern Iowa. Storm chances will be near KALO early in the period. Additional storm may redevelop overnight especially near KMCW after 06z. Outflow from this afternoon`s storms is settling south and may get far enough south to pass KDSM and bring east/northeast wind. This outflow does make wind direction projections less certain and when that outflow will dissipate. Renewed cumulus development will occur on Thursday with scattered showers and storms again developing during the afternoon. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Ansorge AVIATION...Donavon