Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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420 FXUS63 KDMX 201937 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 237 PM CDT Fri Sep 20 2024 .KEY MESSAGES... - Spotty showers and thunderstorms in southern Iowa early Saturday morning, then more widespread thunderstorms in the afternoon and evening, continuing through Sunday. - A few stronger storms are possible on Saturday with pockets of heavy rain possible on Saturday and Sunday (especially in southern Iowa). - Cooler Sunday through next week with highs in the 60s and 70. && .DISCUSSION... Issued at 237 PM CDT Fri Sep 20 2024 High pressure has settled across the area today resulting in plenty of sunshine, mostly sunny skies, and low humidity. Temperatures this afternoon have warmed into the mid to upper 80s this afternoon with dewpoints in the 50s. A quick zoom out on satellite tells us this quiet day will be short lived. Off to the west two phased waves are visible, one across the desert southwest and the other across the northern Rockies. These will move across the area this weekend, bringing chances for stronger thunderstorms and heavy rain through the weekend. The first wave of precipitation will arrive around midnight or shortly after as spotty showers and thunderstorms lift into the area out of Missouri on the nose of a slug of warm air advection out of the southern plains. There is still some variability amongst the CAMs as to placement with most keeping the bulk of the activity into Missouri through Saturday morning. The better forcing arrives later Saturday afternoon when more widespread shower and thunderstorms are expected across the area. MLCAPE is generally near or under 1000 J/kg with modest shear which would prevent better updraft organization. As such, a few stronger storms are possible with hail or a stronger wind gust, but at this time the overall severe threat is on the low side. The southern closed low lifts into the area late Saturday into Sunday, with lingering forcing from a trailing boundary behind the northern wave. This will prolong precipitation across central and southern Iowa on Sunday and into early Monday. PWATs increase in southern Iowa on Sunday, approaching 2 inches. There remains uncertainty as to the placement and precise magnitude of the rain totals for the weekend, but most ensemble guidance indicates southern Iowa will be the winners with lesser amounts north. The EC is the most robust with 2-3" of QPF south of I-80 while the GEFS keeps totals closer to 1.5 inches. HREF guidance is in for the first half of the event and shows pockets of 3+ inches possible in isolated areas. Much cooler air filters in on Sunday with highs in the 60s expected. Temperatures remain cool next week, near to a few degrees below average for this time of year. Precipitation trends into next week are less clear with significant differences between synoptic models middle of next week. The GFS features a large closed low across the area while the Euro keeps this feature well off to the southwest. Details will be refined in the days to come. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1231 PM CDT Fri Sep 20 2024 VFR conditions are expected through the TAF period. Scattered showers and a few thunderstorms will move into southern Iowa after 06z tonight. A few may reach KOTM around or after 12z, however confidence is low at this time so have kept from TAFs. More widespread showers and storms are expected later Saturday afternoon which will be addressed in future updates. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Hagenhoff AVIATION...Hagenhoff