813 FXUS63 KDMX 081713 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1213 PM CDT Tue Jul 8 2025 ...Updated for the 18z Aviation Discussion... .KEY MESSAGES... - Several rounds of storms to end the week, possibly beginning as early as Wednesday night. - Monitoring Thursday into Friday timeframe for very heavy rainfall potential. Stay tuned on this. && .UPDATE... Issued at 428 AM CDT Tue Jul 8 2025 Thunderstorm complex is beginning to move out of the area with some remnant light to moderate rain lingering over far southern Iowa. This system did produce some wind gusts in excess of 60 mph. In addition, a band of heavy rainfall did occur just southeast of the Radar over southwest Ankeny and into the Saylor Township where 5+ inches of rain occurred. This did cause significant ponding in that area but much of this runoff will have a short trip through the Saylor Creek and into the Des Moines river. The Walnut Creek and Four Mile Creek basins did have 1-3 inches across their basins that will cause within bank rises. The precipitation will continue to decrease in areal coverage over the next several hours. Ridge of high pressure will settle back over the state today. Similar to the past several afternoons, model soundings are suggesting the potential for convective temperatures to be reached though there remains some uncertainty how strong if any of an elevated mixed layer settles over Iowa. The uncertainty there along with the lack of another trigger would suggest thunderstorm potential is spotty at best. Per trends, CAMs are likely overzealous on weak convective potential during the afternoon hours today and on Wednesday. Looking ahead, thunderstorm chances may return to the area as early as Wednesday night as the low level jet begins to lean back into Iowa sending waves of theta-e advection across the state. This could lead to another complex of storms moving over portions of central and western Iowa. These storms have been following the more southerly Corfidi vectors and would expect the same here if an MCS does develop. More active weather is on the way for Thursday and into Friday as a stronger upper level system arrives. While some severe weather is possible, monitoring this timeframe for the potential of a Maddox Frontal type of heavy rainfall event. The current setup ahead of the main short wave has an east-west boundary over Iowa with an abundance of Gulf moisture lifting north with 2 plus inch pwats continuously fueled by the low level jet. The global models QPF fields are beginning to pick on this but potentially not the extreme ends that could be possible. Continue to monitor this period! && .DISCUSSION... Issued at 244 PM CDT Mon Jul 7 2025 Early afternoon upper level water vapor imagery from GOES-East shows a cyclonic spin over the southern Manitoba province with the shortwave trough axis into the Dakotas. Convection is ahead of this area while over Iowa there are low level cumulus clouds, particularly over eastern and southern Iowa, with a ribbon of high clouds from southwest into north central Iowa. Temperatures have warmed well into the low and middle 80s and this is nearing the convective temperature in forecast soundings. While there is a slight warm layer aloft, we may be able to overcome this for a few storms this afternoon over southern Iowa with a few storms already over eastern Iowa. With these storms favoring more airmass variety with little available shear, main concern would be sub-severe gusty winds as thunderstorms collapse with this activity diminishing toward sunset. As we head into this evening, will be watching clusters of thunderstorms over South Dakota and northeastern Nebraska start to head southeastward along the MUCAPE axis over western Iowa. These storms could be severe with damaging wind gusts up to 70 mph possible into a few of our western counties such as Sac and Crawford mid to late evening. The outflow looks to push out ahead of these storms making them becoming out of balance. Thus, current expectation is that the severity wanes quickly east of roughly Highway 71 and south I-80. Still, specifier gusty winds of 40 to 55 mph may still occur with this most likely for areas south of I-80 and also likely west of I-35. Rainfall amounts will generally be around or under an inch, though a few places in western or southern Iowa could receive between 1.5 to 2 inches per latest HREF localized probability matched mean. With the expected progressive nature of these storms, not anticipating any short-term hydrology concerns. All of these storms should be largely out of our service area by or shortly after sunrise Tuesday. However, a few showers or storms may continue Tuesday along a surface boundary over southern or eastern Iowa. Additionally, a few storms may try to develop in the afternoon over north central Iowa along the 850mb boundary. Subcloud dry air may contribute to a few gusty winds, but this should all be below severe limits with deep layer shear being less than 25 if not 20 knots. While the previous sentences make it sound wet, expectation is that many places will stay dry during the day Tuesday over central Iowa. High pressure will transit across the region Tuesday night into Wednesday providing a less active period of weather with seasonable temperatures. However, this is short-lived as a shortwave trough off the west central coast moves eastward flattening the Rockies ridge as it nears the state by late Thursday. There will be some phasing of the thermodynamic and kinematic fields and a favorable instability and deep shear space as the shortwave lifts through the region. This will make for periods of thunderstorms from Thursday night through Friday night over Iowa. Strong to probably a few severe storms will be possible in this period per the pattern and supported by various AI and ML guidance. Efficient rainfall processes may be in play with deep warm cloud depths and precipitable water values of 1.5 to around 2 inches, though the heavy rainfall concerns may be mitigated depending on storm speeds. While ensemble means have just a 30% chance of over an inch in 24 hours, the deterministic 0 or 6z GFS, ECMWF, and CMC have between 1 and 3 inches in some 24 hour period between late Thursday and late Friday. Early week soil moisture percentiles are above the the level north of roughly Highway 30 and while there will be some drying between later Tuesday through late Thursday, this area may be more vulnerable to renewed water issues if those rainfall amounts fall over the more vulnerable basins. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1213 PM CDT Tue Jul 8 2025 VFR conditions are forecast through the period, but will be monitoring the potential for fog development around 12z Wednesday. FEW to SCT cumulus may develop this afternoon and perhaps an isolated storm. However, the chance of any storm impacting a site is too low to include any mention. Winds from the northwest will be light at or less than 7 knots through the afternoon. Winds do become a bit variable overnight through the end of the period, though any prevailing direction will likely have a northerly component to it. Regarding fog, confidence with its formation led to no inclusion at this point with uncertainty in cloud cover and the extent of low level saturation. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Donavon DISCUSSION...Ansorge AVIATION...Ansorge