Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Feb 26 2023 08:07:00 FOUS30 KWBC 260806 QPFERD =20 Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 304 AM EST Sun Feb 26 2023 =20 Day 1 Valid 12Z Sun Feb 26 2023 - 12Z Mon Feb 27 2023=20 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE CENTR= AL PLAINS THROUGH THE UPPER MISSISSIPPI RIVER VALLEY... 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 negativel= y-tilted trough. This will result in lee side cyclogenesis and the strength= ening potent surface low to race northeastward toward Iowa by Monday mornin= g. CAMs show convective initiation by around 23z Sunday near the TX/OK Panh= andle, 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 ra= in should be more prevalent along the northern part of the convection and n= ear the surface low, where storms become more elevated and into the comma-h= ead portion of the storm just to the north of the low center. This is also = the typical location of a bookend vortex should bowing segments develop, wh= ich are also known to have locally higher rainfall. Tropospheric moisture c= ontent will be plentifu l (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 deviat= ions 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 amoun= ts 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 a= re most likely to be affected by both the initial line of storms and the co= mma-head region of the low; therefore, running the greatest risk of localiz= ed flooding concerns.=20 There are several factors working against this becoming more of a widesprea= d flooding threat. First, the storms and the developing low will all be mov= ing rapidly towards the northeast as the entire system swings along with th= e 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 h= ow heavy the heaviest 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 dra= in off into the local river basin with little flooding to note.=20 No changes were made to the Marginal Risk area for this morning's update, a= s the guidance has come into good agreement that the area highlighted by th= e Marginal Risk remains the area with the greatest risk of localized flash = flooding, as this corresponds with where the heaviest rainfall amounts are = forecast. Snell/Wegman =20 =20 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 p= ercent. Wegman =20 Day 3 Valid 12Z Mon Feb 27 2023 - 12Z Tue Feb 28 2023 =20 The probability of rainfall exceeding flash flood guidance is less than 5 p= ercent. Wegman =20 =20 Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7ho_W9s7spKmnwxM0IDVnA6r1XNLMz1jVpzLOO1cjZTp= JY06b1Nev0Iy9QXWvESmQol206_bWTD2tc9BThhZNz8Gjtw$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7ho_W9s7spKmnwxM0IDVnA6r1XNLMz1jVpzLOO1cjZTp= JY06b1Nev0Iy9QXWvESmQol206_bWTD2tc9BThhZNHj_rs4$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7ho_W9s7spKmnwxM0IDVnA6r1XNLMz1jVpzLOO1cjZTp= JY06b1Nev0Iy9QXWvESmQol206_bWTD2tc9BThhZGG29uUg$=20 =20 =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) .