Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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455 FXUS63 KDMX 060502 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1202 AM CDT Mon May 6 2024 ...Updated for the 06z Aviation Discussion... .KEY MESSAGES... -Warmer Monday as southeast winds increase with near advisory winds across the northwest. -Strong to severe thunderstorms Monday evening into early Tuesday. Damaging wind and perhaps few tornadoes are the primary hazards. Pockets of locally heavy rain also possible. -Another round of showers and a few storms on Wednesday with localized heavy rain possible, mainly north. && .DISCUSSION... Issued at 245 PM CDT Sun May 5 2024 A rather fine afternoon across Iowa with filtered sunshine along with light winds as surface ridge slides east across the state. Upper low south of the state has some showers approaching southeast Iowa but this is expected to remain south of the forecast area the rest of this afternoon into the evening. Otherwise, quiet conditions persist into tonight as warm advection intensifies ahead of a strong shortwave passing through the Rockies. This continues into Monday with deep southerly flow and moisture returning through the day. Surface pressure gradient tightens considerably with rapid lee side cyclogenesis and southeast winds intensify through the day. This is likely to produce near advisory winds in the northwest by later in the afternoon into the evening. Will not issue an advisory at this time but continue to monitor for potential headline. The moisture return is expected to be in a fairly narrow corridor in advance of the surface boundary with the instability axis reflecting this in a relatively narrow width across Iowa by early Monday evening. The highest instability is in the south and west up to around 1500 J/KG along with strong bulk shear in excess of 40kts. CAMS are all fairly consistent with the development of a linear system in eastern Nebraska during the afternoon with a QLCS passing into Iowa during the evening hours. Instability initially should be sufficient for stable evolution of the system. However as the system progresses eastward, the cold pool is likely to eventually win out as the instability wanes. This makes the west and south the best threat for severe wind gusts and a few tornadoes as SRH values of 200+ m2/s2 will exists ahead of the line. Eventually, the cold pool will overtake the updrafts with the line weakening farther east. Rainfall is also expected to be quick hitting and relatively heavy as PWATs increase to 1-1.5" ahead of the line. While not expected widespread flash flood issues, the heavy rain may lead to renewed river flooding on a few of the basins within central Iowa. Subsidence passes over the state for much of Tuesday with relatively low chances of showers although some showers in the north are possible along a residual boundary. A better chance for additional showers and a few storms arrives on Wednesday as another shortwave approaches the state. An inverted trof acts as a focus for the activity which increases by the afternoon. Both GFS and ECMWF indicate the northern half of Iowa for decent QPF which would only add to any runoff and potential to also induce additional rises or potential flooding on area rivers. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1158 PM CDT Sun May 5 2024 MVFR stratus to move into sites from the southwest, impacting KFOD, KDSM, and KOTM. Cloud bases will rise to VFR, but remain BKN through the afternoon hours. Gusty southeast winds will have gusts up to 30kts after 18z, increasing after 00z ahead of showers and thunderstorms. Cigs are expected to sink to MVFR and IFR with these storms. Have added thunder mention to KFOD and KDSM to reflect initial arrival time. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Cogil AVIATION...Jimenez