


Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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159 FXUS63 KDMX 080552 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1252 AM CDT Tue Jul 8 2025 ...Updated for the 06z Aviation Discussion... .KEY MESSAGES... - A few thunderstorms southern Iowa this afternoon, but most places staying dry. - Severe storms possible over western Iowa mid to late evening into early Tuesday morning. The main hazard is damaging wind gusts up to 70 mph. - Additional shower and storm chances Tuesday with severe weather unlikely. Renewed, widespread storm chances at times Thursday night to Friday night. && .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, subsevere 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 80th 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 /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 1251 AM CDT Tue Jul 8 2025 A line of storms will move across portions of south-central Iowa early on in the period with DSM most likely to be impacted. Brief MVFR/IFR is possible at DSM with a period of heavy rain likely roughly between 06-07Z/Tuesday. Additionally, gusty erratic winds (40+ kts) are possible as the thunderstorm rolls through. Confidence is much lower to the southeast near OTM as the line will be gradually weakening, so have included a PROB30 for thunder in the TAF. Aside from the potential for MVFR ceilings at MCW for a brief time Tuesday AM, VFR should prevail at the terminals for the majority of the day and winds will remain light. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Ansorge AVIATION...Uttech