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Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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463 FXUS63 KDMX 022341 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 641 PM CDT Tue Jul 2 2024 ...Updated for the 00z Aviation Discussion... .KEY MESSAGES... - Threat for severe and flash flooding remains through late afternoon into mid evening. - Quiet but warm on Wednesday - Chances for showers and storms returns on late Wednesday night into Friday. Severe threat appears limited but outdoor activities may be impacted from time to time. && .DISCUSSION... Issued at 354 PM CDT Tue Jul 2 2024 Convection has maintained for much of the morning into early afternoon with a recent uptick as peak heating approaches. Much of the forecast area was overcast through late morning but the past few hours has seen some sunshine across the south with an associated surge in temperatures and dewpoints. MUCAPES of 2500 J/KG have developed into southern Iowa with bulk shear values improving to over 50kts across much of central Iowa. Soundings are also very moist and PWATs have increased to over 2" in the south central - a hydro discussion follows below. Surface flow remains modest at this time although somewhat stronger where mixing has been more robust in the southeast. The severe potential remains decent this afternoon into the early evening although lapse rates are not overly strong which may be limiting updrafts at this point. There is a warm front extending near I80 which may provide some focus for additional strengthening and may be an area for the better threat of severe storms. At this point, damaging wind gusts or a tornado may occur as the system continues to organize with hail remaining an outside threat. The storms pass to the east this evening with drier air arriving overnight as weak surface ridging builds toward the Missouri River Valley in the west. Quiet conditions are forecast into Wednesday with pleasant weather although it will be warm with the drier airmass warming nicely by afternoon. Warm advection begins to increase into Wednesday evening and the overnight ahead of the next shortwave as convection develops across the Plains during peak heating Wednesday afternoon and rides the nose of the low level jet across Nebraska toward southwest Iowa. The bulk of models output suggests this clips the southern counties into Thursday morning. Additional convection is expected near northwest towards north central Iowa as well associated with the upper system passing through South Dakota. This upper low slows to a crawl across southern Minnesota into northern Iowa Thursday night into Friday. This is likley to bring a prolonged period of moderate to locally heavy rainfall in the vicinity of northern Iowa through this time and will need to be watched closely given the very wet conditions that exist in this area. Northwest upper flow then remains in place into next week with several systems sliding into the Midwest. Another system approaches by the end of the weekend with another threat of moderate to heavy rainfall, particularly from the Euro solutions which are slowly with the progress of the system. This continues the threat of renewed river rises or flooding should it come to fruition. && .AVIATION /00Z TAFS THROUGH 00Z THURSDAY/... Issued at 635 PM CDT Tue Jul 2 2024 The line of storms that moved through this afternoon has all but departed the area, with all TAF sites now behind the line. However, some additional isolated to scattered showers are expected to pass through the area through the evening hours. These will be fairly transient, but will keep an eye on them for any impacts to TAF sites. Although the main line is out, MVFR to IFR cloud cover trails the system, and will persist into the evening before seeing improvement in the morning hours. However, moisture and light winds tonight may lead to patchy fog development throughout the area, but confidence is low at this time. Therefore, have included 6SM visibility to capture the most likely time period at each site, and will continue to assess the fog/low visibility potential through the evening hours. && .HYDROLOGY... Issued at 354 PM CDT Tue Jul 2 2024 Threat of heavy rainfall and potential flash flooding continues across central into southeast Iowa with PWATS remaining at to slightly above 2". Morning convection helped to saturate areas of central into southern Iowa with rainfall of 1-3" in many locations. The potential for some training during the late afternoon may be sufficient for localized flash flooding and the Flood Watch remains into the evening for much of the area. The current river forecasts, which includes 48 hrs of forecast precipitation, do slow the fall along the West Fork Des Moines river. Rises are forecast across most other basins including the East Fork Des Moines, Des Moines, Winnebago, Shell Rock, Cedar and Iowa River basins including a return to Minor Flood stage at Mason City, Shell Rock, Cedar Falls and Waterloo, Stratford and Des Moines at SE 6th. This may also bring additional impacts to these areas including the Saylorville Lake storage, which is currently forecast to reach 882 ft by the Corps of Engineers. && .DMX WATCHES/WARNINGS/ADVISORIES... Flood Watch until 1 AM CDT Wednesday for IAZ028-038-039-049- 050-061-062-073>075-083>086-094>097. && $$ DISCUSSION...Cogil AVIATION...Dodson HYDROLOGY...Cogil