Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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404 FXUS63 KDMX 210454 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1154 PM CDT Fri Sep 20 2024 ...Updated for the 06z Aviation Discussion... .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 /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 1150 PM CDT Fri Sep 20 2024 VFR conditions to prevail over the next 6 hours. Low confidence rain at KOTM after sunrise, but will be short lived. Showers and thunderstorms will form along a cold front after 18z, highest confidence near KMCW and KALO. Isolated severe winds possible with storms in the daytime hours. Storms will fill in southward after sunset, reaching KOTM after 06z. Have added in SHRA mentions to reflect timing confidence. Rain will persist well into Sunday across the southern half of the state. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Hagenhoff AVIATION...Jimenez