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Area Forecast Discussion
Issued by NWS Quad Cities, IA IL
Issued by NWS Quad Cities, IA IL
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879 FXUS63 KDVN 102026 AFDDVN Area Forecast Discussion National Weather Service Quad Cities IA IL Issued by National Weather Service La Crosse WI 326 PM CDT Wed Jul 10 2024 .KEY MESSAGES... - There is a chance (40-60%) of scattered showers and thunderstorms this afternoon/evening. An isolated severe storm or two will be possible with heavy downpours, gusty winds, and funnel clouds the main threats. - Increasingly humid Friday and into next week. Heat indices well into the 90s and even low 100s are forecast Sunday and Monday. - Sunday through Tuesday, while thunderstorms will very likely (80%) fail to develop, if they do, severe thunderstorms would be possible. - Moderate to major river flooding continues on the Mississippi River with most sites crested or cresting in the coming days. && .SHORT TERM /THROUGH TONIGHT/... Issued at 258 PM CDT Wed Jul 10 2024 19z WV satellite shows an upper trough advancing south-southeastward over southern MN with multiple shortwaves rotating around this feature over SW MN, IA, and NW IL. Per radar and visible/IR satellite, thunderstorms have already developed in the CWA and two the our west in S central IA. This afternoon and evening, expect additional thunderstorms as temperatures at the surface rise into the 80s and temperatures aloft cool considerably as the upper trough advances overhead, allowing MLCAPE to rise to 1000-2000 J/kg. WHile deep layer shear is lacking, this should be enough buoyancy for stray severe hail to be possible. Additionally, presence of a surface mixed layer suggests a risk for a severe wind gust or two and the otherwise unorganized updrafts collapse, with this risk tempered by the shallow nature of the surface mixed layer, resulting in DCAPE values of only around 800 J/kg. Finally, given the pattern - an upper trough moving overhead, a well-mixed boundary layer, and the presence of outflow boundaries providing areas of vertical vorticity - cannot rule out funnel clouds and a brief non-supercell tornado. Moving ahead to tonight, light winds and near-surface moisture courtesy of the afternoon/evening convection may lead to the development of fog. With GLAMP/HREF/SREF probs suggesting around a 25-35 percent chance for visibility reductions, perhaps even under a mile, have introduced patchy fog into the forecast for a few hours very late tonight. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Issued at 258 PM CDT Wed Jul 10 2024 Thursday, last gasp shortwave looks to rotate southward west of the departing upper trough. A few showers and thunderstorms may develop, but continued lack of shear suggests the chance for a severe thunderstorm is very low. Friday through Tuesday, return flow due to high pressure in the southeastern CONUS will cause conditions to become noticeably more humid with dewpoints in the 70s favored by the weekend. As this occurs, heights aloft build, with the potential result being triple digit heat index values during the afternoon Sunday and Monday afternoons. Along with the potential for hazardous heat and humidity, multiple ridge riding shortwaves look to eject downstream over the Upper Midwest Sunday through Tuesday. Given the moist advection regime described above, MLCAPE may approach 3000 J/kg as winds aloft increase, with sfc-6km bulk shear perhaps topping 40 kts Sunday and Monday evenings. All that said, the operative word in MLCAPE is potential as those warm temperatures aloft will very likely (80%) keep a tight lid on proceedings. Thus, while overall pattern - and CSU ML outlooks - suggest a chance for severe thunderstorms, have only included thunderstorms of any kind in the official forecast for NE IA and NW IL those afternoons. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1242 PM CDT Wed Jul 10 2024 Aviation concerns over the next 24 hours focus on thunderstorms this afternoon and fog early Thursday morning. Probability appears to be great enough (50% or greater) to introduce TEMPO groups at each site. Similarly, with near surface moisture from showers and thunderstorms a good bet and winds becoming near calm late tonight, have gone with a short period of MVFR fog at each site as sunrise approaches. && .HYDROLOGY... Issued at 124 PM CDT Mon Jul 8 2024 Precipitation in the next few days, especially in Iowa, is expected to be dry or very light. Thus, routed flow will continue on all of our rivers. The Mississippi River is currently cresting at major levels upstream of Camanche, IA, and near crest through Illinois City. The crest may take 1 to as much as 3 days to pass. From Le Claire to Burlington, the respective crests will commence within the next 1 to 2 days. Keokuk is now forecast to crest within Moderate Flood category beginning Friday. Gregory Landing is forecast to remain near 19.5 feet through the week. Tributary Rivers: The Cedar River at Cedar Rapids crested below flood stage and will fall over the next several days. On the Cedar River at Conesville, minor flooding will continue. It will see a secondary crest near 14.4 feet Wednesday night into Thursday. The Wapsipinicon River at Dewitt is forecast to remain in moderate flooding category through late on Friday. The Iowa River at Oakville is seeing high water levels due to backwater affects from the Mississippi River. It is forecast to remain near 11.4 or 11.5 feet through midweek and then rise to near 12.1 feet late Thursday into Friday. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...None. IL...None. MO...None. && $$ SHORT TERM...ARX/77 LONG TERM...ARX/77 AVIATION...ARX/77 HYDROLOGY...Gunkel