Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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787 FXUS63 KDMX 052344 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 644 PM CDT Sun May 5 2024 ...Updated for the 00z 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 /00Z TAFS THROUGH 00Z TUESDAY/... Issued at 641 PM CDT Sun May 5 2024 VFR conditions to prevail over the next 6 hours as midlevel cloud deck continues to move off to the east. Additional cloud cover fills in from the southwest overnight, blanketing terminals through the daytime hours. Chance for some MVFR cigs at KFOD and KDSM through the morning. Left SCT deck at KFOD due to lower confidence. MVFR cigs at KOTM possible for the duration of the afternoon hours. Showers and storms begin to arrive at KFOD near the very end of the TAF period. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Cogil AVIATION...Jimenez