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Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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859 FXUS63 KDMX 131732 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1232 PM CDT Tue Aug 13 2024 ...Updated for the 18z Aviation Discussion... .KEY MESSAGES... - Patchy fog early this morning with some lingering drizzle/mist possible southwest half. - Showers and thunderstorms return late tonight into Wednesday and again Wednesday into Thursday. Heavy rain and a few strong to severe storms are possible. && .DISCUSSION... Issued at 358 AM CDT Tue Aug 13 2024 Active pattern ahead over the next several days with multiple rounds of showers and storms starting late tonight and continuing into Thursday. Prior to that, we start the day today with patchy fog that has been locally dense at times with visibilities as low as 1/4 to 1/2 mile. Lowest visibilities have mainly been transient through the early overnight hours precluding a fog headline at this point but a SPS remains in place. Fog should dissipate shortly after sunrise though some lingering drizzle/mist is certainly possible underneath the stratus deck which is firmly in place over roughly the southwest half of the state. With additional cloud cover moving in later today into tonight, sunshine may be harder to come by for all but the northeast but even then may be filtered today with upper level smoke moving into the state from western wildfires. Temperatures as a result remain below normal through much of the area and in the 70s with areas northeast potentially seeing the highest max temperatures. Theta-e advection increases late tonight into early Wednesday with showers and storms returning to the forecast ahead of a low lifting out of KS/NE overnight into Wednesday. The nose of an increasing 35- 45 knot low level jet will help keep rain/storms going through the night and although can`t completely rule out some stronger storms with moderate shear, generally weak instability should limit storm strength. Pwats of 1.5 to nearing/exceeding 2" will keep a locally heavy rainfall threat nearby, but guidance into 12Z Wednesday mainly keeps the highest QPF values just outside of our area for the most part with a localized 1-2" amount possible in the far southwest. How activity evolves through the night and the amount of lingering cloud debris Wednesday morning will have a significant impact on our next storm threat Wednesday night into early Thursday as the next wave moves through. Forcing overall looks a bit stronger with the potential for much higher values of instability if atmospheric recovery can occur. Soundings suggest the potential for long, looping hodographs with low LCLs putting all hazards on the table if surface-based convection can be realized. Depending on storm mode and the effects of early day activity/clouds, some strong to severe storms are certainly possible with wind or hail, as well as another heavy rain threat with pwats near to exceeding 2" again fueled by a stronger low level jet. Will need to continue to monitor trends through the day but see SPC Day 2 Marginal (Level 1/5) to Slight (Level 2/5) Risk for further details. Additional storms are possible on Thursday into early Friday before another break in activity occurs through at least part of the upcoming weekend as an upper level ridge builds in. Temperatures return to more normal levels with increasing humidity values by mid-late week into the weekend. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1232 PM CDT Tue Aug 13 2024 MVFR to IFR stratus across the area is starting to break up but will continue to impact sites through the afternoon. Winds will start to increase tomorrow morning ahead of the next approaching system, with gusts around 20kts. A few showers may reach KFOD/KDSM/KOTM at the end of the current period as overnight storms in southwest Iowa weaken and lift into central Iowa through the morning. For now have kept from TAF as there is uncertainty as to how scattered they will become by the time the reach TAF sites. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...KCM AVIATION...Hagenhoff