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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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422 FXUS63 KDVN 151755 AFDDVN Area Forecast Discussion National Weather Service Quad Cities IA IL 1255 PM CDT Thu Aug 15 2024 .KEY MESSAGES... - Ongoing mainly elevated MCS on track, with minimal severe risk.However, heavy rainfall with the 1.9 to 2.1 inch PWAT feed indicated by SPC mesoanalysis still looks like the main impact this morning. Ponding of water in urban areas still looks feasible due to high rainfall rates. - A severe risk remains for this afternoon and evening with all modes of severe weather possible if storms can develop locally/in the DVN CWA. The most likely time frame for severe storms looks to be 4 to 10 PM. - After a chance for a few isolated showers on Saturday, a pattern change will bring mainly quiet weather over the rest of the weekend and for the first half of next week. Temperatures look to be near normal. && .SHORT TERM /THROUGH TONIGHT/... Issued at 325 AM CDT Thu Aug 15 2024 Today...Large upper wave/MCV seen on several types of imagery currently rolling acrs western into central IA ATTM, with leeside warm air advection wing elevated MCS the main show locally. Brunt of other south to southwestern flank convection will continue to feed south and southeastward acrs MO along better instability gradient. But the local activity will continue into mid morning before supportive 20-30 KT south/southwesterly LLJ diurnally diminishes. Looks like a low chance for any severe/precip loaded microburst winds this morning, but the high PWAT feed mentioned above fueling high precip rates will produce swaths of 1-3 inches of rain by the time it winds down later this morning. Thus ponding water and some nuisance urban/small stream flooding still possible. Then the same uncertainty comes into play of how fast the convective debris decays to allow for the potential warm up of temps in the 80s and sfc DPTs in the 70s to make for high instability with model projected SBCAPEs of 3000-4000+ J/kg. MLCAPEs may breach 3000 J/kg. These kind of buoyancy levels with the main upper trof axis and sfc front approaching from the west inducing effective shear values of 35-45 KTs could be trouble if sctrd convection can take off locally. All modes of severe including tornadoes would be possible, and large hail up to golf ball size. But again with the debris needed to clear/thin in time to get the heating and those CAPE values, as well as the air getting worked over currently, a lot of convective uncertainty exits. Fcst soundings show convective temps in the mid to upper 80s, and fcst high temps very challenging with the potential of values ranging from the mid 70s to mid/upper 80s. Could also see the scenario where very little or isolated convection occurs on the fringes of the DVN CWA and more coverage areas/prime convective initiation grounds take off to the east and south of the local fcst area. But still with the chance of isolated to sctrd strong storms firing in the CWA by late afternoon or early evening, with have to cover with the adequate CHC POPs. Again if they go locally, expect supercell structures and all modes of severe possible with the southern into central CWA the most likely initiation zones. Tonight...After the evening storm/shower chances or activity decreases, westerly post-frontal sfc winds will help temps drop into the 60s through Friday morning. Will bank on lingering cloud cover and the west wind speeds themselves to limit any fog production, but it may still have to be kept in mind acrs the heavy rainfall areas and sfc winds decouple. Spotty to isolated showers may linger in the south and east to after midnight in lingering lift zones adjacent to the passing boundary. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Issued at 325 AM CDT Thu Aug 15 2024 Friday...Model ensembles continue with the idea of the upper trof evolving into a seasonably large cut-off upper acrs the northwestern GRT LKS at week`s end. Cyclonic steering flow wrapping around this feature, with embedded vort spokes and more importantly steepening low to mid level lase rates will likely produce isolated to sctrd afternoon into evening showers and even some thunderstorms. The northeast half of the DVN fcst area will be more at risk of this activity. Fcst soundings show developing inverted-V soundings, and other thermodynamic/kinematic vertical profiles that would support a stronger cell being able to produce hail and downburst wind gusts. Even a passing shower may produce wind gusts of 40-50 MPH if the 40- 45 KT top of the mixed layer is correct. The deep mixing profiles will make for breezy west winds Friday afternoon, and make the most of the thermal profiles for warm high temps in the mid to upper 80s in many locations. Saturday through Sunday...Latest suite of medium range ensembles and upper jet progs now suggest the upper trof to remain adjacent to the area enough to produce more isolated to sctrd afternoon showers in the east on Saturday. Then eastward trof migration and northwesterly steering flow amplification acrs the mid to upper MS RVR Valley should make for a dry and seasonable Sunday. Monday through Wednesday...Longer range progs suggest higher amplified northwesterlies to the lee of large plains/Rockies upper ridge complex, making for near to slightly below seasonable temps. Western GRT LKS sfc ridge to prevail with fair weather. The area may then be suspect to a clipper type wave in the steering northwesterlies for a precip chance sometime by mid next week. && .AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 1239 PM CDT Thu Aug 15 2024 IFR to MVFR ceilings with low clouds will continue this afternoon with some breaks towards the late afternoon and evening. If some clearing is realized, some showers and thunderstorms are expected to develop and traverse the area during the evening hours. This would bring some MVFR conditions in storms, but otherwise VFR conditions should prevail. MLI and BRL will have the best chance for seeing showers or storms so introduced a prob30. CID might see some storms near 00Z before they more east, but opted to leave mention out due to the uncertainty of development and placement. Overnight some visibility reduction into MVFR category may be seen, but left mention out of TAFs at this time. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...None. IL...None. MO...None. && $$ SHORT TERM...12 LONG TERM...12 AVIATION...14