868 FXUS63 KDMX 162350 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 650 PM CDT Wed Apr 16 2025 ...Updated for the 00z Aviation Discussion... .KEY MESSAGES... - Elevated fire weather conditions through the remainder of this afternoon; gusty breezes prevail into Thursday - 20-30% chance of a few storms over southern and eastern Iowa toward and after sunrise Thursday morning with any activity diminishing by midday. - Storm chances increase as high as 60 to 80% north of US 34 late afternoon into the evening hours. Severe storms possible with main severe hazard being large hail. Initial storms before and around sunset west of roughly Highway 169 could have damaging wind gusts and perhaps a tornado. - More seasonal temperatures this weekend with renewed shower and storm chances Sunday. && .DISCUSSION... Issued at 200 PM CDT Wed Apr 16 2025 Upper level water vapor imagery shows mid-level ridging pushing into the state while an upper low is off the California coast with a shortwave trough over western Canada. Early afternoon visible satellite imagery has varying degrees of high clouds spread across Iowa while low level warm air advection is ongoing. Temperatures are well above normal well into the 60s and 70s this afternoon. Gusty winds from the southeast are prevailing along with relative humidity values between 20 and 30% resulting in elevated fire weather conditions. There have been a handful of fire hotspots - mainly prescribed burns - detected by satellite through the veil of clouds. Into tonight, a wave of strong low level theta-e advection in concert with a 30 knot low level jet develops ahead of a lead shortwave trough passing over the state. Convective allowing models (CAMs) are more muted in their signal of convection toward daybreak Thursday compared to previous runs of the global models. While there is still a chance of an isolated severe storms or two with large hail over our southern or eastern forecast area toward daybreak into Thursday morning (e.g. MPAS suite vs other CAMs), this is less likely than thought in previous days. Any ongoing storms are expected to wane in the morning as the low level jet weakens and an elevated mixed layer (EML) spreads over the state ahead of surface low pressure moving over eastern Nebraska. There looks to remain quite a bit of cloud cover at varying levels per the latest HREF cloud cover guidance. However, if the cloud cover ends up being less than forecast, forecast temperatures may need to be boosted as they are near the 25th percentile of the initial National Blend of Models guidance. The EML should cap off any storm development in the afternoon until closer to or shortly before sunset when storms are expected to quickly develop along a cold front stretched over northwestern Iowa into east central and southeast Nebraska. Forecast soundings from the 12z HRRR and 9z RAP show potential for a brief window of surface based storms, but this is conditional on the boundary layer heating sufficiently to overcome any lingering inhibition. If surface based storms do form, there could be 1000 J/kg or more of MLCAPE and the hodographs also show favorable low level turning for rotating storms (supercells). However, winds between 500m and 1 to at times 2km show less speed shear such that this keeps low level storm relative helicity (SRH) values low. While large hail will be the main severe concern, damaging wind gusts and a tornado may be possible in this window around sunset. With the loss of daytime heating coupled with a restrengthening EML, any surface based storms will transition to elevated storms. Interestingly, the full hodograph becomes elongated as the LLJ develops, but with storms transitioning to elevated they will likely be only realizing more of a linear hodograph. With good ventilation and steep mid-level lapse rates, the main concern here would be large hail. Storms are expected to weaken and lessen in coverage later in the evening and especially after midnight. While there may be some lingering showers into Friday morning, the western Canada trough elongating back into the southwestern US will aid in pushing the cold front through the area with increasing subsidence and cold air advection behind it. Additional convection is likely along the front, but this looks to be just southeast of our forecast area at this time later Friday afternoon. The cold front will stall south of the state and should result in dry conditions on Saturday. Deterministic models agree that a shortwave trough will track over or near the state late in the weekend. This along with ensemble means from the various global of the probability of a tenth of an inch of precipitation point to renewed shower and storm chances around Sunday. && .AVIATION /00Z TAFS THROUGH 00Z FRIDAY/... Issued at 649PM CDT Wed Apr 16 2025 VFR conditions are generally anticipated into the evening with nothing beyond patchy mid and high level cloudiness. A few periods of MVFR visibilities due to smoke cannot be ruled out, but confidence is insufficient to mention at any particular location at the moment. There is some potential for showers east into the early morning hours Thursday. Thunder may briefly occur as well, but confidence is too low to include until short term trends note otherwise. At least MVFR stratus is expected to overspread central IA Thursday as low level moisture increases. Although not mentioned as of yet, chances for thunderstorms will increase at or just beyond the valid period (18/00z) into Thursday evening. && .DMX WATCHES/WARNINGS/ADVISORIES...None. && $$ DISCUSSION...Ansorge AVIATION...Small