659 FXUS63 KDMX 010342 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1042 PM CDT Sat May 31 2025 ...Updated for the 06z Aviation Discussion... .KEY MESSAGES... - Warm temperatures and smoky skies continue today into Sunday. Some surface smoke possible, mainly west. - Shower and thunderstorm chances return to the area late Monday night, lasting through Tuesday into early Wednesday. Potential for severe weather and heavy rainfall, mainly Tuesday night. && .DISCUSSION... Issued at 247 PM CDT Sat May 31 2025 A nearly perfect end to May has been slightly squandered by the wildfire smoke that continues to stream south out of Canada today, filtering sunshine and muting what would otherwise be blue skies over Iowa. Fortunately, most of this smoke has remained aloft through mid-day, keeping the impacts limited to the gray skies. Its possible some light concentrations of smoke will diurnally mix down to the surface this afternoon, as evidenced by the HRRR and RAP smoke models. However, the smoke aloft has been thinning out on visible satellite through the day and ceiling observations imply that the smoke aloft is at around 20 kft. Therefore, confidence is pretty low in this happening. As we get into the evening, a shortwave passing to the west of the forecast area will pull another plume of smoke down behind it. Reduced visibilities and haze/smoke have been observed in the Dakotas, indicating that subsidence behind the wave has allowed smoke to work its way down to the surface. Most of this smoke should remain to the north and west of the forecast area, but we may still see some spill into the northwestern portions of Iowa. Even then, this smoke should be spreading out and dispersing as it continues south. Weather conditions remain generally the same through Sunday as upper level ridging builds in from the west, keeping temperatures warm and skies smoky. HRRR and RAP smoke modeling suggests another chance for smoke to diurnally mix down to the surface tomorrow afternoon in western Iowa a similar signal to todays. However, tomorrows surface smoke may be more plausible than todays given the recent shortwave passage, so will want to keep an eye on that through tonight and into tomorrow. Any air quality impacts tonight or tomorrow will be assessed by the Iowa DNR. Upper level ridging continues eastward over the area on Monday but will be short lived as two waves begin to merge into broad troughing Monday night into Tuesday. This will bring the return of showers and thunderstorms to the forecast area. Showers and storms in the area begin with the initial push of theta-e advection starting late Monday night into Tuesday morning. Instability will be fairly low (< 1000 J/kg) overnight, but will have support from a moist low level jet to help precipitation along through the night. Showers and thunderstorms persist through the day on Tuesday low and mid level moisture transport persist through the day. As we progress through the day on Tuesday, the cold front will slowly track north with instability increasing ahead of it, and maximizing in the eastern half of the state by Tuesday afternoon. This currently looks to be the most likely time and location for severe weather, given the current guidance. Deep layer shear wont be overly impressive ahead of the front (~30 to 40 kts of 0-6 km shear), but there will be a modest supply of low level shear (also ~30 kts of 0-1 km and 0-3 km shear). Likewise, looping hodographs boast 100+ m2/s2 of SRH, although become quite messy further aloft. All this to say there is certainly the potential for organized storms and severe weather on Tuesday afternoon, although will want to see how high resolution guidance handles the saturated profiles from the overnight and morning convection. Better shear will be present along and behind the cold front, which may indicate the potential for linear storms along the boundary, but this will also be better discerned by the high resolution models. The storm prediction center has issued a Day 4 15% risk for severe weather (comparable to a slight risk, which is level 2 out of 5) for the eastern half of the forecast area on Tuesday, echoing this potential for strong storms. Finally, in addition to the severe weather chances, anomalously moist profiles will be present with this system as the gulf opens up, resulting in precipitable water (PWAT) values of 1.8 2 over much of central Iowa through Tuesday. These values are roughly 175 to 200% of typical values in central Iowa this time of year (average PWAT is around 0.90 to 1.00), which suggests the potential for some decent rainfall. Grand ensemble probabilities for over 1 of rainfall in 24 hours is roughly 50 to 60% over central Iowa and NBM probabilities for 1 of rainfall in 24 hours is similar, but with a band of slightly higher probabilities around 60 to 70% in central Iowa. A few deterministic models also suggest an area of 2+ rainfall over southern Iowa. Area rivers should be able to handle an inch or two of rainfall, but will certainly want to monitor for any higher amounts Tuesday given the moisture profile present. Precipitation moves out Wednesday morning, with another wave passing to our south Wednesday night into Thursday, although guidance is a bit split on if this will reach up into Iowa. Will continue to evaluate conditions into the second half of next week through the coming days. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 1042 PM CDT Sat May 31 2025 Incoming smoke remains mainly aloft over Iowa, with smoke reaching the surface over much of the Dakotas and now edging slightly into northwest Iowa. Potential for surface visibility reductions is the main concern tomorrow, although confidence is still low in timing and intensity. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...DMD AVIATION...Dodson