Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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402 FXUS63 KDMX 041736 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1236 PM CDT Sat May 4 2024 ...Updated for the 18z Aviation Discussion... .KEY MESSAGES... - Thunderstorms passing across Iowa early this morning into early afternoon with low end wind and hail risk. - Additional strong to severe storms on Monday evening into Tuesday && .DISCUSSION... Issued at 331 AM CDT Sat May 4 2024 A surface low has ejected across the central plains and towards the midwest through the overnight. Convection has ridden the surface warm front into the area with storms persisting thanks to low-level jet reinforcement. By 3 AM storms were entering western parts of the area, but have lost some steam thanks to weak instability into Iowa as the primary axis falls short of the area. This line of storms will continue progress across the area through the morning, exiting east in the early afternoon. MLCAPE through today remains around 500 J/kg with rather modest lapse rates, though deep layer (0-6 and 1-6 km) shear within sounding comes in at 40-50 kts. Given the parameter space, expect some small hail and wind risk with storms, however the severe threat remains on the lowers side into the afternoon. At the same time, hydro concerns remain in the back of our minds. Given recent heavy rains in recent days, a few areas are more sensitive (rivers in northern Iowa in minor flood and south-central Iowa which saw flash flooding earlier in the week). The good news here is that storms are fairly progressive which will mitigate most issues. HREF LPMM places a widespread 0.75-1.0" across the area with a few pockets of 1.5+" possible. Sunday will bring a welcome reprieve in the active period with weak ridging into the area behind the departing low. This is short-lived as the next system will be on our doorstep, swinging across the Rockies. By Monday will will move across the plains. In Iowa this will make for a breezy afternoon as the pressure gradient tightens ahead of the system. Recent model runs have slowed the progression of the system, lifting it across Iowa later Monday evening and into the overnight before exiting on Tuesday. A plume of instability cuts across the area with 1500+ J/kg MLCAPE and deep layer shear exceeding 40 kts. Model soundings indicate tall skinny CAPE profile with sweeping hodographs through the lowest 2 km. With 0-1 km SRH exceeding 200 m2/s2, tornadic activity is something to be aware of, in addition to the hail and wind concerns. The week remains active with another system on Wednesday/Thursday. Details on this will be forthcoming as this system is closely associated with the Monday/Tuesday system and will be heavily influenced by it. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1235 PM CDT Sat May 4 2024 Widespread MVFR ceilings are expected this afternoon with breezy northwest winds. The ceilings dissipate this evening as winds decouple and become much light. Patchy fog is likely late tonight given residual moisture across much of central Iowa along with the weakening winds. VFR conditions are expected into Sunday as surface winds increase from the south. && .DMX WATCHES/WARNINGS/ADVISORIES...None. && $$ DISCUSSION...Hagenhoff AVIATION...Cogil