Area Forecast Discussion
Issued by NWS Quad Cities, IA IL
Issued by NWS Quad Cities, IA IL
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362 FXUS63 KDVN 250752 AFDDVN Area Forecast Discussion National Weather Service Quad Cities IA IL 252 AM CDT Sat May 25 2024 .KEY MESSAGES... - A pleasant day is on tap to begin our Memorial Day weekend, with lots of sunshine - Yet another storm system moves in late tonight through the day Sunday, which will support more chances for strong to severe thunderstorms - Chances of showers and a few storms will remain with us Sunday night and Monday - Drier conditions return for Tuesday through Friday && .SHORT TERM /THROUGH SUNDAY/... Issued at 251 AM CDT Sat May 25 2024 As we kick-off our Memorial Day holiday weekend, the weather conditions this weekend will be a mixed bag, with very pleasant conditions today, but a more active day for Sunday. For today, an area of high pressure will build in, which will bring plenty of sunshine with it. If you have any outdoor plans today, it looks like a great day for them! Light and variable winds this morning will turn more southerly as the high pressure system moves east, with southerly winds between 5 to 15 mph expected this afternoon. High temperatures should warm to the middle to upper 70s. This respite from storms will be short-lived, though, as our next storm system moves in late tonight, lasting through the day Sunday. A broad upper-level trough will develop over the Intermountain West region today, with a sub-tropical upper-level jet nosing into the Corn Belt region tonight into Sunday. An area of low pressure will undergo lee cyclogenesis over eastern Colorado today, and both the GEFS and ENS ensembles are progging the low to translate towards our region tonight. Ahead of the surface low, we will contend with a 35 to 45 kt nocturnal low-level jet, which will help enhance the effective shear magnitudes. As a mid-level shortwave impulse ejects from the central Plains, convective initiation will follow and approach our area. Storms appear to move into our region after midnight tonight, but the CAMs show some disagreement on the onset timing of the storms. Still, with the LLJ in place, steep mid-level lapse rates of around 7 to 8 C/km above a low-level inversion, and most-unstable CAPE values around 500 to 1500 J/kg, a large hail threat will be in place. There may also be a lower end tornado threat, mainly due to the orientation of the southwest to northeast 0-3 km bulk shear vectors. CAMs appear to indicate that the convection tonight into Sunday morning will be more disorganized compared to the MCS that moved through Friday morning, but if anything can organize and generate an east to northeast propagating surge or bow, this could tap into this shear to generate some mesovortex-genesis tornadoes. SPC continues to carry a Marginal Risk (level 1 of 5) for severe weather from Independence, IA to Charlotte, IA to Galva, IL and points southwest of this line. Eventually, the Sunday AM convection will end by around noon Sunday, but we aren`t out of the woods yet. There is some uncertainty on how the Sunday afternoon storm potential will play out, but eventually, the aforementioned surface low will translate through our region Sunday PM. If the surface low moves overhead, the more favorable zone for severe convection will shift south of our area, where a more pronounced baroclinic zone should establish. As the surface low moves through, winds will turn more northerly in our area, per the latest suite of CAMs. We may still get some scattered showers and storms, but the focus for severe weather should largely be south of us. Surface-based CAPE Sunday afternoon will increase to between 1000 to 2000 J/kg, but the low-level shear won`t be as strong due to a lack of LLJ. The mid-level jet will remain strong to our south, with upper-level divergence overhead, so modeled hodographs are oriented more straight with very little curvature. At this time, SPC has kept mainly a Marginal to Slight Risk for severe weather in our region, but they have trimmed down the Enhanced Risk, which matches better with my thoughts. The Enhanced is still in place for Hancock and McDonough counties in west-central Illinois. I would be interested to see what SPC does with their new Day 2 outlook that will be issued early this afternoon. The CSU machine-learning severe probs continue to paint decent probabilities for severe weather across our south and east, with all hazards possible, with the most favorable probabilities being for damaging winds and large hail. Finally, some more heavy rainfall is possible with the Sunday activity, given Pwat values around 1.3 to 1.7. IVT per the ENS ensembles are over 97 percent of climatology, so water vapor transport will be supportive of heavy rainfall. NBM probabilities of 1" of rain with the tonight/Sunday precipitation are around 50 to 70 percent for a large portion of the region, so ongoing river flooding will only be exacerbated with this rainfall. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Issued at 251 AM CDT Sat May 25 2024 The long-term period will start off with the remnants of the Sunday convection lingering as the mid-level trough translates through the region. There will be a brief break in showers and storms early Monday before yet another chance of showers moves in ahead of an approaching mid-level shortwave that will dive southeast from the Dakotas. Mixed-layer CAPE appears to be pretty meager, with values progged around 500 J/kg, so we might be contending with showers than thunderstorms. For Tuesday through Friday, we are looking at something we haven`t had in a while: an extended stretch of dry and quiet conditions! Guidance is progging a long-wave ridge over the western CONUS and a surface high pressure settling across the western Great Lakes region for much of next week. Temperatures look to be seasonal, with highs in the 70s for most locations, and lows in the 50s. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 1213 AM CDT Sat May 25 2024 VFR conditions are expected throughout the TAF period as high pressure builds into the region. Light and variable winds this morning will develop for a time before winds turn southerly around or after noon around 5 to 10 knots. && .HYDROLOGY... Issued at 1025 PM CDT Thu May 23 2024 The flood warning for the North Skunk River near Sigourney has been upgraded to Major flood category. Routed water from a sparse data area upstream where the heaviest rain fell a few days prior has led to a rapid rise in the last 6 hours and is now above Major flood stage. The forecast calls for a crest of 24.5 feet by Friday afternoon, but there is uncertainty in the amount of water that remains to move through the reach and the crest may need to be further adjusted. The Wapsipinicon River near DeWitt was upgraded to a Flood warning. Major flood stage is being forecast based on routed flow, and is supported in output from the Hydrologic Ensemble Forecast Service Model Simulation (HEFS), which places high confidence on reaching Major Flood stage (12.5 feet). The forecast has gone up this evening with a crest now over 13 feet next week. This fits near the most likely range from HEFS of 12.8-13.1 feet. Some attenuation is possible as the routed flow moves through the river system, but at the same time there will be additional rounds of rain Friday and Sunday of which could total over 1 to 2 inches. There will likely be changes to the forecast in the coming days as the rain lays out and the extent of the routed flow is better known, so stay tuned! Routed water and additional rain through the weekend is leading to rises on most other tributary rivers and the mainstem of the Mississippi, especially south. Flood warnings or watches are in effect for portions of the Cedar, Iowa, Skunk and southern sections of the Mississippi river so please refer to the latest Flood Statements and Flood Warnings for details. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...None. IL...None. MO...None. && $$ SHORT TERM...Schultz LONG TERM...Schultz AVIATION...Schultz HYDROLOGY...McClure