


Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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245 FXUS63 KDMX 100415 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1115 PM CDT Wed Jul 9 2025 ...Updated for the 06z Aviation Discussion... .KEY MESSAGES... - First round of storms arrives late tonight into Thursday morning. Heavy rain is the primary concern. Localized amounts exceeding 3 inches possible (40% confidence). - Severe weather enters the picture tomorrow with wind being the primary threat. A tornado or two cannot be ruled out. - Heaviest rainfall expected Thursday night with more severe weather potential returning Friday afternoon. && .DISCUSSION... Issued at 249 PM CDT Wed Jul 9 2025 The peak of the H850 ridge was centered over central into southern Iowa this morning with a moisture plume of 12C+ over Nebraska. The main moisture transport axis is noticeable from the festering convection in eastern Nebraska. A secondary moisture axis, albeit high-based and shallow, will be the catalyst for a few scattered showers and storms this afternoon. Updrafts will be narrow and short- lived along this boundary. Highs will top out just below 90 degrees, warmest across the south. The main sequence of an extended string of active weather begins in the west tonight as the aforementioned moisture plume is advected in along the LLJ. The orientation of the LLJ won`t change much at all until a front arrives late Friday night. We`ll be set up for heavy rainfall. PWATs around the 2 inch mark along with warm cloud depths exceeding 3500m make for efficient rainfall production and less ice introduction. The LLJ will nearly match the vector of the mean wind, orienting Corfidi vectors to the south, albeit low in magnitude. This means that any MCS that forms will naturally propagate southward and into the instability axis, helping to maintain its intensity. Storm motions will be slow, leading to localized high rainfall amounts. Overall, the N-S QPF swath in most guidance makes sense spatially with amounts exceeding an inch in this max region commonplace. Given the rainfall benefactors mentioned above, can`t rule out localized amounts reaching or exceeding 3 inches. Strong cold pools from the moisture content will allow for gusty winds with the main MCS clusters, but with this threat sparse and fleeting due to weak effective shear (<20 kts) at this point in time. An EML will begin to build in along the southwest flow and will focus the moisture away from the low-levels and steepen lapse rates during the day. Meanwhile, a PV anomaly from northern CA will flatten the upper- level ridge, opening Iowa to a series of synoptic shortwaves from the Intermountain West. Mesoscale features will also be in play due to any remnant outflow/debris from overnight activity. Much of the 12z CAM guidance produces an MCV in central Iowa which would be a local enhancement to lift--and available vorticity for tornadogenesis. While these smaller scale features will not be accurately known until presently analyzed, they boost the potential for continued precipitation through Thursday. Both on the CAPE gradient and potentially at peak heating above the EML where moisture is preserved. Gusty winds will again be possible with storms in the afternoon, but the primary hazard will again be heavy rain. The primary shortwave arrives Thursday night along with another push of 2 inch PWATs and favorable warm cloud depths. The orientation of LLJ again lurks over western and central Iowa, this time with a stronger moisture transport magnitude. This time period will contain some of the heaviest rainfall of the week, aided even more by a stalled warm front somewhere across the state. Another widespread 1-2"+ and locally higher amounts will be along this front. The triple point then approaches the weakly- capped environment on Friday. Deep-layer shear parameters along the warm front favor severe weather, although some of the model output could be bloated by simulated cold pools. Surace-based parameters at the mercy of mesoscale debris in the warm sector. Trends will be monitored. The cold front will then be dragged across the state Friday night into early Saturday, bringing more rain, this time appearing more progressive due to it being a cold front. More synoptic energy arrives by Sunday, but the moisture content at this time appears questionable. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 1109 PM CDT Wed Jul 9 2025 VFR conditions with light winds still prevail early this overnight period, though clouds are continuing to increase west to east with with storms moving towards the Missouri River. These storms will continue to push eastward through the overnight period reaching KFOD first, by around 09Z and then other sites thereafter, but confidence is higher in northern sites (KMCW) and KALO, though thunder more questionable by the time storms reach KALO. Similarly, some questions remain in southward extent, but KDSM likely to see at least rain if not storms too, with KOTM generally more on the southern edge. Have updated to prevailing or tempo groups based on latest guidance but adjustments may still be needed as storms move into the area. Heavy rain may decrease visibilities more than currently indicated while stronger storms, especially west near KFOD, could have some gusty winds. Additional shower/storms are possible Thursday afternoon into evening with greater confidence late Thursday night into Friday morning, but confidence in timing/impacts too low to include explicit mentions at this time. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Jimenez AVIATION...05