581 FXUS63 KDMX 141743 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1243 PM CDT Thu Mar 14 2024 ...Updated for the 18z Aviation Discussion... .KEY MESSAGES... - Areas of showers and storms likely through the morning and into the afternoon. Threat of severe weather has decreased. - Critical fire weather conditions may develop Saturday. && .DISCUSSION... Issued at 224 AM CDT Thu Mar 14 2024 Overnight radar imagery is full of activity with widespread shower and thunderstorms stretching from NE/KS and through northern MO into southern Iowa. This is all associated with an upper shortwave that has broken off from a large parent upper low closing off over the western conus. The most intense thunderstorm activity so far has remained just south of the state within the deeper instability axis, generally along and south of a surface warm front. Showers and storms have bled north into southern Iowa, however stubborn dry air has chewed into progression and coverage with northerly extent. A few stronger cores remain possible in far southern Iowa through early morning, posing a threat for small hail and gusty winds. Rain gauges in the area suggest up to 0.75" has fallen in a few areas, so pockets of 1"+ amounts are certainly possible before this activity pushes east later this morning. Focus for rainfall chances shift further north this morning and afternoon as a fractured mid-level def zone moves through. Again, a very dry airmass sitting just off to our north and east will impinge on the precipitation shield and limit the spatial extent of appreciable QPF. Still looking at the potential for 0.25" to 0.50+", mainly between Hwy 30 to Hwy 18 and lesser amounts or even no additional rainfall to the north and south. Conditions clear out tonight as the dry air spills back south in the mean northwesterly flow behind the departing wave. While no precipitation is expected through the weekend, fire weather concerns crop up Saturday as a front sweeps south through the state. Deep boundary layer mixing behind the front + dry airmass should have no problems undercutting NBM dewpoints, which like most model guidance has exhibited a high bias with dewpoints in recent days. Taking the 25th percentile of NBM guidance lowers RH values into the 20% range during the peak heating hours. Winds near the top of the mixed layer are ~30-35 kts and should have little trouble transporting to the surface within deeply mixed, unidirectional northwest flow. Conditions turn cool and blustery Sunday into Monday as a deep upper low dives into the Great Lakes and shoves a colder airmass southward into the region. Wind chills come Monday morning will be in the single digits and teens, a far cry from the warmth we've seen as of late. The cool spell does not last long as warm air advection returns by mid-week beneath building heights aloft, sending temps back above normal with highs in the 60s looking likely. && .AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 1236 PM CDT Thu Mar 14 2024 A widespread mix of cigs across Iowa early this afternoon ranging from IFR to local LIFR over southern Iowa to improving conditions over northern Iowa with VFR expected at KMCW by early this afternoon and possibly as far south as KDSM by late afternoon. An area of rain over central Iowa will slowly diminish through the afternoon before ending. Cigs will then improve with VFR expected at most sites by late this evening. A northeast wind will increase later this afternoon and evening before diminishing into Thursday. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Martin AVIATION...Martin