Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Oct 29 2023 07:06:48 FOUS30 KWBC 290706 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 305 AM EDT Sun Oct 29 2023 Day 1 Valid 12Z Sun Oct 29 2023 - 12Z Mon Oct 30 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM EASTERN TEXAS INTO THE MID-SOUTH & LOWER OHIO VALLEY...=20 =20=20 ....Southern Plains into the Ohio Valley...=20=20 Precipitable water values will be in slow decline this period, maximizing in the 1.75-2" range early on before falling into the 1.25-1.5"range by Monday morning. A positively-tilted upper level trough will be approaching the region from the west and north causing some forward progression to the front across Texas and the Lower Mississippi Valley with time. The degree of low-level inflow and effective bulk shear available could organize convection into training bands Sunday morning, assuming sufficient instability, as the flow is fairly uniformly out of the west-southwest with height. MU CAPE of 250-500 J/kg should be sufficient to achieve hourly rain totals of 1-2" at times early on, which would be a problem across area terrain and places that rained heavily thus far, but the 00z NAM indicates the instability fades with time on Sunday and Sunday night. Local amounts in the 2-4" range are indicated by the available guidance overall. The size/extent of the Slight Risk area has as much to do with current soil saturation and ongoing heavy rainfall as it does with the possibility of additional heavy rainfall. There was some temptation to raising the threat level to a Moderate Risk, but the minimal/declining instability forecast remains the biggest drawback.=20 =20=20 Roth Day 2 Valid 12Z Mon Oct 30 2023 - 12Z Tue Oct 31 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent.=20 =20 Interior Southeast Texas... The 00z UKMET, 00z Canadian Regional, and 00z NAM advertise 1-2" rains across portions of this area along a slowly progressive front. There have been pockets of 300%+ of average weekly rainfall in this region, which has led to 3 hourly flash flood guidance being below 3". While precipitable water values are sufficient for possible issues -- in the 1.5" neighborhood -- instability will be scant, generally under 250 J/kg per 00z NAM forecasts. This should lead to hourly rain totals under 1".=20 Believe the risk of excessive rainfall is non-zero, but not high enough to achieve the 5 percent threshold at this time. Should guidance trend upward on the instability, a Marginal Risk could be considered at a later time. Roth Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-cwLvZNhU1caTp2mn0svuMestqiLWzUe7kq3mA7rB6DC= hXXPVaDdRRdrXFof84S1BGYQA-QsHwJwRld5ug1G596EhM4$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-cwLvZNhU1caTp2mn0svuMestqiLWzUe7kq3mA7rB6DC= hXXPVaDdRRdrXFof84S1BGYQA-QsHwJwRld5ug1GTtPdBBI$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-cwLvZNhU1caTp2mn0svuMestqiLWzUe7kq3mA7rB6DC= hXXPVaDdRRdrXFof84S1BGYQA-QsHwJwRld5ug1GLzeh3pM$=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) .