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Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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627 FXUS63 KDMX 200854 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 354 AM CDT Sat Jul 20 2024 .KEY MESSAGES... - Scattered showers with a few thunderstorms off and on through the weekend into early next week. Overall severe weather threat remains low, though a locally heavy downpour is possible. - Continued mild through the weekend with highs in the 70s followed by gradual warming through the upcoming week. && .DISCUSSION... Issued at 350 AM CDT Sat Jul 20 2024 Overall pattern continues to feature an upper ridge over the western U.S. and a closed low over Canada north of the Great Lakes with a broad trough in between. This trough remains fairly stagnant through about mid-week keeping off and on shower and storm chances in the forecast today through about Wednesday. A shortwave nudging into the region helped kick off precipitation last night though amounts overall remain more minimal into the early overnight hours through much of the area, a few hundredths to a few tenths, as of 2AM. The exception is over southwest Iowa where precipitation amounts and rates have been a bit higher with amounts approaching 0.5 to 1" closer to the Omaha area. This shortwave will be very slow moving today through Sunday as it crosses into and through central Iowa. As a result, early day scattered showers will continue to slide eastward through the morning hours with additional widely scattered shower or storm development this afternoon into evening. Forcing remains weak with instability limited and shear minimal today thus making the main hazard, if any storm can form, lightning or a localized heavy downpour as otherwise any storm that does form will likely be pulse storms, up and down quickly given the limited shear to work with. Although uncertainty remains high in exact location of showers/storms at any one time due to the scattered nature, chances are highest over western into northern Iowa (roughly the western third of the state) where HREF probabilities of 24-hour QPF over 0.5" ending at 6Z Sunday are 40- 60%, with a few localized higher values of 60-80%. Still can`t rule out funnel cloud potential if any clearing can occur with the low coming across the area providing good surface vorticity. 0-3km CAPE looks to reach upwards of 100-200, depending on the model, mainly over northern into western Iowa, however, NST (non- supercell tornado) parameters in the NAM and GFS indicate localized areas in parts of central to eastern Iowa as well. If any activity does occur, it should be limited to peak heating and dissipate by this evening. As we get into tonight, some drying may occur. Given our overall light winds which are expected to continue through Sunday, any pockets of clearing could lead to some patchy fog potential, especially north or west. Scattered showers or a few storms will remain in the forecast on Sunday, especially during the afternoon into early evening. Although instability actually looks to be higher on Sunday, shear and forcing continues to remain weak keeping storms generally non-severe, but the funnel cloud potential will remain during peak heating on Sunday and may even be higher than today. Periodic shower/storm chances continue into mid-week with the overall pattern remaining unchanged, as mentioned previously, and weak impulses moving through the overarching flow at times. Most of these chances Monday-Wednesday will remain diurnally driven with the bulk of any shower/non-severe storm activity during the afternoon to early evening. Temperatures this weekend remain in the 70s with a slight warming trend through the week with temperatures remaining in 80s, but approaching the upper 80s to even the return of some 90s by next Friday into Saturday. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 1152 PM CDT Fri Jul 19 2024 Scattered light showers are around KDSM/KFOD currently and will be in the vicinity early in the period. Cigs will gradually decrease later tonight and into Saturday and there will be a period of MVFR at times near at all sites except KOTM and could have locally IFR near KFOD. Conditions will gradually improve later in the afternoon and into the evening. Light winds will continue and be 8 kts or less. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...KCM AVIATION...Donavon