Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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845 FXUS63 KDMX 242006 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 306 PM CDT Mon Jun 24 2024 .KEY MESSAGES... - Heat Advisory into the evening across central and west. Heat Advisory in the southwest on Tuesday - Severe potential and heavy rain potential return central and south on Tuesday into Tuesday night. - More convection potential on Thursday night into Friday with additional heavy rainfall across portions of central Iowa. && .DISCUSSION... Issued at 305 PM CDT Mon Jun 24 2024 Sultry airmass has pushed back into the state this afternoon with heat index values of 100-110 across much of central into western Iowa. The heat advisory has been extended up to the I35 corridor to include the Des Moines metro and Ames areas. Otherwise, warm mid level temperatures with +12C at 700mb has pushed across much of the forecast area during this afternoon. This has effectively capped convection for the moment across central Iowa despite MUCAPE values of +6000 J/KG in western Iowa. Convection is more likely to develop farther north into Minnesota later today along the northern edge of the cap and then scoot southeast, possibly clipping the far northeast counties of the forecast area but more likely remaining to the northeast of our area. This convection is expected to produce strong to damaging winds as it pushes to the southeast into the overnight along with locally heavy rainfall. Otherwise, the airmass remains very warm and muggy into tonight with lows in the 70s. Tuesday into Tuesday night is setting up as a complex forecast as a weak boundary settles into the state during the day. The hot and muggy conditions persist south of the front with near heat advisory conditions once again in far southwest Iowa and have included a small advisory for that area. Otherwise, CAMS continue to indicate some convective development by mid to late morning near the convergence boundary in central Iowa somewhere near the Highway 30 or Interstate 80 corridor. Some training of this appears possible into the afternoon and some locally heavy rainfall may occur. Outflow from this and the placement of the boundary are likely to affect the eventual evolution of convection into Tuesday evening and night with central and southern Iowa remaining the most likely areas for storms. Damaging wind remains the biggest concern with the storms later in the day into Tuesday night given the strong instability and decent downdraft CAPE. Some large hail may also occur as well. This convection moves swiftly to the southeast on Tuesday night and exits into Missouri and Illinois. Wednesday into Wednesday night is quiet with drier and cooler air overspreading the state in the wake of the front. The bulk of Thursday is also relatively tranquil, however moisture and warm advection return with a vengeance by the evening as strong low level flow from the southwest pushes into western Iowa. Convection is likely to spread into the west during the evening and push across much of central Iowa during the overnight. A strong low level jet around 50kt will feed moisture rich air into the state maintaining convection overnight along with PWATS around 2" leading to locally heavy rainfall and the potential for some severe weather. This convection lingers into Friday with possible redevelopment ahead of a boundary pushing across the state. Eventually, subsidence arrives by late day into Friday night with cooler and drier air for much of the weekend. However, the active pattern returns into early next week with additional chances of rainfall. && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 305 PM CDT Mon Jun 24 2024 Mostly VFR conditions for much of the period with convection edging along the north and east portions of the forecast area. Convection may begin to increase in coverage toward the end of the forecast period, mainly along the KDNS-KDSM-KCID corridor. Surface winds remains south to southwest this afternoon with the gustiness decreasing this evening as mixing decreases. Winds begin to switch to the northeast across northern Iowa by the end of the period as a weak boundary dives into the state. && .HYDROLOGY... Issued at 305 PM CDT Mon Jun 24 2024 Major to historic flooding continues along portions of the West Fork Des Moines River as well as mainstem Des Moines River above Saylorville Lake. There has not been much in the way of changes to going forecasts, however the river may fall more slowly in expected due to upstream readings in Minnesota. If we do make any changes to the forecast in the Des Moines basin or elsewhere the changes would likely be downward slightly. Looking ahead to potential rainfall through the week, the most immediate concern for heavier rainfall will be Tuesday, as most of the rainfall today is expected to avoid our forecast area. Fortunately for those being impacted by river flooding in northern Iowa, the higher QPFs currently favor southern Iowa, and even if heavier rainfall develops north, it will quickly drop south with the front. That being said, any heavy rainfall could still delay improvement to flood conditions, if only briefly. Additional shower and thunderstorm chances are expected again Thursday night into Friday. That additional rainfall may either result in quicker rises, higher crests or slower falls. When it comes QPF its location, amounts and timing are everything in terms of the river response. Make sure to stay up to date on the latest forecasts and river information, and use extreme caution in flooded areas. && .DMX WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 8 PM CDT this evening for IAZ004>006-015- 016-023>025-033>036-044>048-057>060-070>073-081>083-092>094. Heat Advisory from noon to 7 PM CDT Tuesday for IAZ070-081-082- 092>094. && $$ DISCUSSION...Cogil AVIATION...Cogil HYDROLOGY...Zogg