Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Feb 26 2023 15:52:57 FOUS30 KWBC 261552 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1052 AM EST Sun Feb 26 2023 Day 1 Valid 16Z Sun Feb 26 2023 - 12Z Mon Feb 27 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE CENTRAL PLAINS THROUGH THE UPPER MISSISSIPPI RIVER VALLEY... Forecast remains on track regrading the expected developing convection across the central Plains tonight and expanding into the Upper Mississippi Valley through early Monday as a strengthening low pressure system moves northeast. The only notable change to the Marginal Risk area in the 16z update is to include more of northwest Illinois given the somewhat susceptible soil there from previous rainfall and light snowmelt. The upper-level low currently over the Southwest is expected to eject into the southern High Plains by tonight while opening up into a sharp negatively-tilted trough. This will result in lee side cyclogenesis and the strengthening potent surface low to race northeastward toward Iowa by Monday morning. CAMs show convective initiation by around 23z Sunday near the TX/OK Panhandle, which should organize into a QLCS within a few hours and move east. While the individual storms will certainly be capable of locally heavy rain, they will be fast moving and start out scattered along the line. Heavy rain should be more prevalent along the northern part of the convection and near the surface low, where storms become more elevated and into the comma-head portion of the storm just to the north of the low center. This is also the typical location of a bookend vortex and potential larger scale MCV should bowing segments develop, which are also known to contain locally higher rainfall. Tropospheric moisture content will be plentiful (tapping into both the eastern Pacific and western Gulf of Mexico), with PWATS into the 1-1.5" range. These moisture values are 4-5 standard deviations above the climatological mean and above the 95th percentile according to both the 00z EC & GFS. However, the fast-moving nature of the developing storm system will limit excessive rainfall potential. Total rainfall amounts in the Marginal Risk area are currently forecast to be in the 1-2" range, with CAMs only showing a maximum of 3.5" possible. The Marginal Risk area from central/eastern Kansas to far southwest Wisconsin covers areas that are most likely to be affected by both the initial line of storms and the comma-head region of the low; therefore, running the greatest risk of localized flooding concerns. One area of concern that will be evaluated for a potential upgrade to a Slight Risk with this evenings update is from central Iowa to far northwest Missouri. This area appears to have the greatest threat of repeating showers and thunderstorms, but should still remain relatively short-lived. There are several factors working against this becoming more of a widespread flooding threat. First, the storms and the developing low will all be moving rapidly towards the northeast as the entire system swings along with the aforementioned trough as it joins the 110 kt southwesterly jet. Thus, no one area will see very heavy rainfall for very long. Second, instability is moderate, with MUCAPE values peaking near 1,250 J/kg. The relative lack of instability should hinder how strong the cells can get, which will limit how heavy the intense rainfall will be. Finally, most of the Marginal Risk area has dry antecedent conditions, with soil percentiles on average at 10-20% saturated. Any areas that pick up heavy rain may see that rainwater drain off into the local river basin and limit flooding impacts. Snell Day 2 Valid 12Z Mon Feb 27 2023 - 12Z Tue Feb 28 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 3 Valid 12Z Tue Feb 28 2023 - 12Z Wed Mar 01 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-_3tZ7sG5jlRN5YS8JLO9noEiszdck2eldPZ05kRvsbt= aSjtCQTuzPXYoCIHEWNm_4Eo9WfmAtojgBBVEJF5hBDDoFA$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-_3tZ7sG5jlRN5YS8JLO9noEiszdck2eldPZ05kRvsbt= aSjtCQTuzPXYoCIHEWNm_4Eo9WfmAtojgBBVEJF5M47pS7U$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-_3tZ7sG5jlRN5YS8JLO9noEiszdck2eldPZ05kRvsbt= aSjtCQTuzPXYoCIHEWNm_4Eo9WfmAtojgBBVEJF55PC3oQw$=20 $$ =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .