Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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623 FXUS63 KDMX 072347 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 647 PM CDT Tue May 7 2024 ...Updated for the 00z Aviation Discussion... .KEY MESSAGES... - Scattered showers & storms possible into the night - Chances for showers and storms Wednesday into Thursday. Potential low overall, but severe weather still possible late Wednesday. - Less active to end the week and into early next week with normal to above normal temperatures && .DISCUSSION... Issued at 343 PM CDT Tue May 7 2024 Isolated showers and storms have begun to develop in daytime heating, a few with the lingering theta-e axis far east, and others higher based in the drier air west associated with approaching weaker mid level forcing, which will continue spotty chances into the early morning hours Wednesday. Otherwise, the sprawling parent upper level low will move little into tomorrow and induce a weak surface reflection/inverted trough into western Iowa during peak heating, which will also be aided by a lobe of the aforementioned increase in mid level kinematic forcing. The storm environment is interesting and somewhat nebulous with weak low level shear 1km and below, but strong deep 6-8km shear and extremely elongated hodographs aloft along a sharp north to south gradient (much higher south). While the 500-1500 J/kg MLCAPEs are not alarming, steep low level lapse rates are a good percentage of that (200+ J/kg 0-3km CAPE) with strong shallow updraft stretching potential. This parameter space leads to multiple hazardous weather concerns during the afternoon and evening hours. Even though low level kinematics such as shear and streamwise vorticity are weak, thermodynamically dominate funnels/weak tornado potential is there along and ahead of the inverted surface trough in what will likely be sub-1km LCLs. This would be more favorable with discrete cells farther south realizing the deeper shear and taking on the much slower Bunkers RM motion (<20kts) versus a strong 30-40kt mean wind. Some 2-5km updraft helicity tracks are evident in the 12Z HREF as well, supporting supercell potential coincident with the noted thermodynamics, and there is also some signal in AI/Nadocast guidance. Weak low level shear under much stronger deep shear and elongated hodographs would also be favorable for hail production. Going into the early evening, the stronger mean wind should subside as the upper low is finally on the move and approaches leading to slower cell movement. Although the moisture parameters are fairly season, this slow movement could also lead to locally heavy rains with HREF PMM QPF suggesting isolated 2-4 amounts are possible north. Looking into Thursday, Low level focus and overall synoptic scale lift is weaker, however moisture lingering in the trailing cyclonic flow will lead to at least some chances for showers and a few storms through the day. A strong Upper MS Valley short wave, whose primary response will remain to our northeast, will start a period of relatively inactive northwest flow aloft until the pattern breaks down early next week with little model agreement on how that will unfold. && .AVIATION /00Z TAFS THROUGH 00Z THURSDAY/... Issued at 640 PM CDT Tue May 7 2024 VFR is widely expected to prevail across the TAF sites. Towards the last few hours of the period, showers and storms are expected to develop across the area, potentially affecting all TAF sites. However, have shied away from mentions with this issuance given timing being last couple/few hours of the period. Otherwise, a few enhanced wind gusts may yet be experienced this evening with showers, but coverage and confidence is too low to time out within current TAFs. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Small AVIATION...Curtis