


Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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345 FXUS63 KDMX 161758 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1258 PM CDT Wed Jul 16 2025 ...Updated for the 18z Aviation Discussion... .KEY MESSAGES... - Rain and storms to clear out faster today, with a heavy rain setup possible in southern Iowa tonight (60% confidence in rain). - Multiple chances of heavy rain this weekend. Slight Risk ERO out for multiple days in a row. && .UPDATE... Issued at 239 AM CDT Wed Jul 16 2025 An MCS moved into Iowa ahead of schedule overnight with most of the model guidance available initializing too far west geographically. Have translated this discrepancy into the PoPs by accelerating the departure of precipitation by about 2 hours. The line of storms that moved through Omaha zapped the main instability axis as expected, so the severe threat in the short term dwindles. Could see some gusty winds where the line of storms latches onto the warm front. Another feature of note is an MCV that has formed in Northwest Iowa. This will keep precipitation going across the north through the morning hours. Scattered convection will also be possible immediately ahead of the MCS due to the LLJ angled into the state. The main baroclinic zone will move across the state during the daytime and usher in dry air from behind, this being the culprit for such cool low temperatures across the north Thursday night. Its trailing cold front will stall somewhere near the IA-MO state line tonight. The mean wind and LLJ will have similar direction and will be blowing parallel to the stalled front, appearing similar to a Maddox frontal pattern for heavy rain. Corfidi vectors point parallel to the orientation of the front, meaning there will be training storms in a prime heavy rainfall environment. PWATs upwards of 2.5" with warm cloud depths over 4000m are collocated. Soundings also have a long, skinny CAPE profile in the warm sector, helping lift parcels evenly throughout the profile. While most guidance keeps the heaviest rainfall south of the state for now, have still preserved PoPs in the overnight period for southern Iowa. The thinking is that location issues could persist through the entire model run. The surface low this afternoon could be further northeast than what is displayed, meaning it would have pulled its cold front further north. The RRFS supports this thinking, the 00z run being one of the models closer to spatial reality. It has the H850 boundary firing off in the bottom row of Iowa counties, producing over 2 inches of QPF along the way. In this regime, there will be spots along the front that overperform, making a push at 5 inches. High pressure gives us a brief pause on Thursday and gives us comfortable temperatures in the process. Highs will only be in the 70s. All eyes then turn to the weekend as that stalled boundary doesn`t really go anywhere, and it will be subject to upper-level northwest flow as well as an open plume of Gulf moisture aimed near the state. The upper-level jet comes into play come late Saturday, so add some deep-layer shear to the mix. && .DISCUSSION... Issued at 256 PM CDT Tue Jul 15 2025 Another warm and humid afternoon is ongoing with temperatures in the 80s and dew points in the 60s to 70s resulting in heat indicies in the upper 80s to upper 90s across the area. Flow out of the south to southwest will continue to bring in moisture off the Gulf into Wednesday morning ahead of the approaching low-level low which will be moving through southern MN through the daytime Wednesday dragging a cold front with it through the state into Wednesday evening. Attention first is on the developing convection in Nebraska this afternoon into evening which will progress eastward towards the Missouri River into late tonight, maintained in NE by a 30-40 knot LLJ. The overall parameter space into our far western CWA will make it difficult for storms to stay in balance with current thinking in line with previous and recent CAM trends of decaying convection moving into western Iowa near to after midnight before any lingering activity continues to push eastward into early Wednesday morning. Although can`t completely rule out a strong storm as the line initially enters our far western CWA, overall expecting any storms to be sub-severe. For any strong storms that can maintain into western Iowa, strong wind gusts are the primary threat followed by locally heavy rain, though activity should be progressive enough to limit the hydro threat overall, especially after several dry days now. What remains uncertain is the coverage and timing of the decaying storm activity into central Iowa and beyond which has significant implications on the any storm development later in the day Wednesday. The aforementioned cold front will be drifting southward through the area through the day and setting up somewhere near the IA/MO border into Wednesday afternoon. Pending any other lingering outflow boundaries/mesoscale details after the morning activity, this is likely where additional development will occur during the afternoon to evening but this boundary in CAMs is anywhere from south central Iowa into northern Missouri making it difficult to pinpoint at this range where the better storm threat is. As noted yesterday, the better shear lags behind the boundary even though instability blossoms in the warm sector south of the front. There remains enough of a favorable environment for a few strong to severe storms develop in the afternoon to evening, especially over southern Iowa, if not further south, but at this point remains conditional on frontal location, amount of early day clearing, and any other mesoscale details. The primary threat will remain strong wind gusts and locally heavy rainfall once again, though the potential placement of rain over southern Iowa is also the area which can take the most amount of rain given antecedent conditions and continuing maturing crops. The LLJ is not as robust on Wednesday night into Thursday, but may help maintain some rain/storms over far southern Iowa into the night before clearing into Thursday morning. High pressure drifts into and through the area later Thursday into Friday with cooler temperatures moving in behind the frontal passage as well. This will bring some pleasant days to end the week with temperatures in the 70s to low 80s. Active weather returns late Friday into the weekend, however, with multiple additional chances for showers and storms at times. Details remain uncertain at this range, but will continue to monitor trends. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1241 PM CDT Wed Jul 16 2025 Lingering rain showers from the overnight activity continues to diminish early this afternoon in the northeast with the main aviation impacts from the lingering lower ceilings with a combination of VFR to MVFR CIGs prevailing at midday. A few IFR CIGs may occur at times as well, especially north to northeast, into this evening though extent of and timing of lower ceilings, especially north, remains a bit more uncertain and updates may be needed. Additional rain chances may impact KOTM late tonight into the early overnight but kept with prob30 group due to location uncertainty with activity potentially occurring south of the terminal. Widespread improvements expected into Thursday morning as VFR conditions return to all terminals. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Jimenez DISCUSSION...05 AVIATION...05