Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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954 FXUS63 KDMX 091958 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 258 PM CDT Tue Jul 9 2024 .KEY MESSAGES... * A few scattered showers/thunder north this evening. * Expanding/more widespread showers/thunder Wednesday. * Low-end scattered shower/thunder chances at times Sat/Sun - best east. * Heat builds in late week/weekend - HI Values into 100s by Sun && .DISCUSSION... Issued at 255 PM CDT Tue Jul 9 2024 Beryl remnants continue to slowly churn NE into/through the region, with its center currently working through the MO/IL/KY/TN intersections. With regards to sensible weather, precip from Beryl will only just clip far SE Iowa today/tonight and expanded cloud cover into central Iowa will suppress high temperatures a degree or two today. Otherwise quiet overall conditions may be briefly disrupted by a few scattered shower/thunder opportunities over northern Iowa later this afternoon and evening with a combination of sunshine/deep mixing and little to no cap. With very weak wind profiles, these would be transient and short live in nature with only real risk being lightning. More widespread opportunities for showers/thunder will begin to present themselves late overnight as a stronger compact shortwave rides southward through the mean flow, on the backside of the exiting Beryl remnants. This has been well advertised and continues to be well resolved in guidance, so have generally kept with near likely PoPs, but have hesitated to go much higher with expectation of hi-res/CAM depictions predominantly scattered in nature. Similar to yesterday and potential showers/thunder later today, little expectation for much more than some moderate to heavy rain and lightning. Strongest updrafts may produce some small hail with MUCAPE depictions around 2000 J/kg, but unlikely anything will be able to sustain long enough or tap into full CAPE potential to produce a notable severe threat with continued weak wind profiles and moist profiles overall. As previous discussion noted, a landspout may be possible with supportive low level stretching progged, especially with likely outflows around to help product areas of vorticity. Wednesday will be the end of the most notable precipitation opportunities across the area within the going forecast. Though as the area remains supplanted within NW large scale flow, compact embedded shortwaves may produce periodic opportunities for a few scattered showers and storms, as noted within deterministic synoptic models at times Friday through Sunday. Very hard to latch onto anything of note at this time with timing and location variances, so have kept with the low end NBM PoPs at this time. Of more not through the weekend will be the building heat as western heat dome begins to ooze into the central CONUS. Bulk of the heat remains expected to stay W/SW of the area, but enough will build in by late weekend to see highs rise into the low to mid 90s and heat index values into the lower 100s deg F. This is all well aligned within NBM with MaxT spreads of only a couple/few degrees through the weekend. Uncertainty grows substantially into next week though with spreads reaching 10 to 12 degrees or so with guidance uncertain on evolution of northern stream shortwaves and heat dome evolution. Another aspect to casually watch is Td`s may be a little low given all the recent moisture and peak agriculture ET ongoing this time of the year. Low 70s Td`s are bad enough already, but could be closer to mid-upper 70s at times. Primary consequences there would be possibly suppressing MaxTs a degree or two, but also pushing heat index values closer to 110 deg F. Regardless, be prepared for uncomfortable temperature and humidity conditions this weekend and into early next week. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1238 PM CDT Tue Jul 9 2024 VFR conditions will prevail for much of the period. This afternoon a few scattered thunderstorms are possible in northern Iowa. Higher chances for impacts are at KMCW for a few hours. It is possible an isolated storm may reach KFOD, however with less confidence have kept from the TAF for now. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Curtis AVIATION...Hagenhoff