Area Forecast Discussion
Issued by NWS Quad Cities, IA IL
Issued by NWS Quad Cities, IA IL
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084 FXUS63 KDVN 280305 AAB AFDDVN Area Forecast Discussion...UPDATED National Weather Service Quad Cities IA IL 1005 PM CDT Sat Apr 27 2024 .KEY MESSAGES... - Active period continues into the overnight and also into Sunday. - Flash flooding remains a concern overnight into Sunday morning for areas that will have received repeated rounds of storms south of I-80, and this is where a Flood Watch continues. - Scattered severe weather remains possible, mainly well south of I-80 overnight, but also into Sunday although prior convection may have an impact on the magnitude/timing/location of severe weather Sunday PM. - Unsettled weather continues through next week, with periodic rain chances. && .UPDATE... Issued at 1002 PM CDT Sat Apr 27 2024 The primary expectations for the forecast largely continue on track as we head into the overnight hours. An isolated severe risk continues, and a potential for a developing flash flood threat in mainly the Flood Watch area will be something we have to monitor closely with regenerating thunderstorms. A mesoscale convective vortex (MCV) near the Iowa/Wisconsin/ Illinois border region will continue to shift northeast through midnight, dragging a somewhat decaying line of thunderstorms eastward in the zone along/north of I-80. An associated cold pool from the storms` longevity should help continue to push this too east of the CWA. Further south and southwest of our area too, a low-level jet of 45-50 kt as observed on upstream profilers in western Missouri will support isentropic lift along/north of the outflow-modified boundary. This will likely result in storms in central/northern Missouri to continue to thrive with even new development possible to the west of these, all of which will likely clip or advance over the southern CWA. It may depend on cold pool magnitude that develops with this convection in Missouri, as there already is an ongoing meso-high in southeast Iowa "shoving" things along. If that is sufficient enough of a push, it may take the brunt of the severe threat mainly south or just clip the southern tier. Severe winds are the main threat, but cannot rule out a brief tornado threat given still high values of low-level CAPE, especially ahead of the outflow boundary. Of greater concern is the training storms in the southern CWA in a high moisture transport environment. Looping the radar in Missouri shows some attempts at backbuilding, and RAP forecast Corfidi vector do become 5-10 kt across the far south between 05Z-09Z. Similarly, if the cold pool development is sufficient, it may propagate the heaviest rainfall rates along too and just south/southeast of the CWA, but confidence in that occurring is low at this time and the threat still very much includes our south. Given the wet conditions in this area from Friday (1-1.5 inches) and already this evening (additional 0.5-0.75 inches), this area is primed for a flash flood risk if 1+ inch per hour rates set up for 2-3 hours. && .SHORT TERM /THROUGH MONDAY/... Issued at 140 PM CDT Sat Apr 27 2024 Late morning surface analysis shows a surface low centered across eastern Minnesota and western Wisconsin, with a cold front draped to its south across east central Iowa and northwest Missouri. Off to our southwest, another surface low with a warm front and dry line was centered over the Oklahoma panhandle, with storms ongoing along this and ahead of a shortwave in the same location. This shortwave will progress northeast over the next few hours, and will be the driver of our weather over the next couple of hours. The overall forecast remains on track for the area, with shower and storm coverage expected to increase over the next few hours. The first round should be focused along the stalled cold front draped across east central Iowa as we destabilize and reach our convective temperature in the upper 70s. Latest CAMs focus the threat mainly along and northwest of the HWY 151 corridor. Ample 0-6km shear and steep mid-level lapse rates pushing CAPEs around 1000-2000 J/kg may lead to storms capable of large hail initially. The second round of storms will come this evening as the aforementioned shortwave rides the front and drives additional lift across the area. A renewed LLJ will also ensure ample lift and increased vertical shear. There remains some uncertainty as to where storms will initiate and track, which is likely tied to early PM convection and how much it stabilizes that warm sector air in eastern Iowa. Regardless, HREF ensembles continue to paint areas mainly south of Interstate 80 with high POPs. Severe storms will also be possible with mainly a large hail and damaging wind threat with near straight hodographs and cold pool dynamics in play. While low, can`t rule out a tornado threat in the QLCS and with any remnant boundaries from early PM storms. Look for this threat to wane by midnight, with concerns turning more towards a heavy rain/flash flood risk. Speaking of which, we will need to keep a close eye on flash flooding potential with these storms. LLJ will advect in a rather robust PWAT feed across the region with values approaching 1.75" by midnight. Where storms do train, latest CAMs show QPF by Sunday morning approaching 2-4 inches. This looks to be favored mainly in southeast Iowa, west central Illinois and northeast Missouri, where a Flood Watch is now in effect through Sunday morning. Heading into Sunday, scattered showers and storms will persist through the morning and early afternoon, with a renewed round of more widespread linear showers and storms expected by the evening ahead of another robust shortwave ejecting out of the Rockies. There is potential for this activity to become severe, with the Storm Predication Center advertising a Level 1 to 2 risk for the area. The primary threats with storms will be damaging winds and large hail, with a secondary tornado threat if low-level shear can materialize. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Issued at 140 PM CDT Sat Apr 27 2024 Post cold front passage, we will be in for a dry start to the week with high pressure moving across the central Plains and mid-Mississippi River Valley. By mid to late week, a renewed round of showers and storms is expected for the area as a trough in the Rockies ejects several shortwaves across the Plains and Midwest. && .AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 613 PM CDT Sat Apr 27 2024 A stormy period will be in place this evening, with thunderstorms widespread before 06Z in eastern Iowa and northwest Illinois. Winds will potentially exceed 40 kts along and south of Interstate 80 through 04z. Otherwise, thunder may become more sporadic overnight, with rain and mvfr cigs continuing. Sunday, a gradual improvement to higher MVFR to low VFR is expected, with another round of storms moving in during the afternoon from west to east. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...Flood Watch through Sunday morning for IAZ087>089-098-099. IL...Flood Watch through Sunday morning for ILZ025-026-034-035. MO...Flood Watch through Sunday morning for MOZ009-010. && $$ UPDATE...Ervin SHORT TERM...Friedlein LONG TERM...Speck AVIATION...Ervin