Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Apr 01 2023 15:57:15 FOUS30 KWBC 011557 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1156 AM EDT Sat Apr 01 2023 Day 1 Valid 16Z Sat Apr 01 2023 - 12Z Sun Apr 02 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Locally heavy rainfall remains probable across portions of AL/GA into the FL panhandle. However amounts exceeding flash flood guidance appear unlikely, and thus we opted to remove the Marginal risk with this update. A line of strong to severe thunderstorms is expected to move across portions of PA/NY this afternoon. While these storms will produce briefly heavy rain, the quick movement of the cells should generally prevent a flood threat. There is some chance we could see localized urban high water across portions of eastern PA towards NYC as storms enter a slightly more unstable environment with higher lower level dewpoints. However, even here storms will be moving so quick that the flood risk should be low. The overall environment certainly favors severe weather as the main impact with this activity, and thus while the urban minor flood threat is non-zero, we will continue to go with no areas in the ERO. Chenard Day 2 Valid 12Z Sun Apr 02 2023 - 12Z Mon Apr 03 2023 A southern stream shortwave interacting with a Gulf Coast warm front along with sufficient moisture/instability is expected to produce locally heavy rainfall from eastern Texas into the Lower Mississippi Valley. Its general progression should keep amounts from becoming particularly extreme. Some low- to mid-level frontogenesis tracking roughly between the ArkLaTex, near the AR/LA border, and through the ArkLaMiss into MS, but even amongst the GFS and NAM guidance the axis of such is different. As the placement remains a question mark due to the north-south spread in the guidance, with the 00z Canadian Regional unusually on the southern side and the 00z NAM remaining up north. The ECMWF has been steadily shifting northward. Instability and low-level inflow/effective bulk shear should be sufficient for convective organization. Hourly rain totals up to 2" with local amounts in the 2-4" range are expected in this region. A couple narrow swaths of 1-2" of rainfall fell Friday into Friday Night across southern AR and from northeast TX across northern LA and should have saturated soils to some degree. The Slight Risk remains in place and like the QPF splits the difference in the guidance.=20 =20 Roth Day 3 Valid 12Z Mon Apr 03 2023 - 12Z Tue Apr 04 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL IN AND AROUND SOUTHERN AL & THE FLORIDA PANHANDLE... While there are differences amongst the guidance mass fields, there is a general signal for a moisture plume with precipitable water values at or above 1.5" to become stuck vaguely near the FL border with AL and GA. Instability, low-level inflow, and effective bulk shear appear sufficient for convective organization. The flow should be fairly unidirectional with height from the west-southwest, leading to concerns for cell training. With low-level inflow slightly convergent, cell mergers can't be ruled out either. The low- to mid-level frontogenesis seen on Sunday should be exiting to the east and northeast. The guidance spread in amounts is fairly wide, with the 00z NAM the driest and the 00z ECMWF the wettest, showing local amounts of 5". Soil moisture across portions of southern AL and the FL Panhandle and Big Bend is elevated, and rainfall during the day Saturday (and possibly Sunday) could lead to further saturation. The model guidance has a general signal for 1-3" in this area, which could fall as quickly as an hour or two. Considering the above, a Marginal Risk area was added for this region. Roth Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6BmdBjzrvzZaLaHp8zCQZ7JGjrw4Jes_1WFV64-MspDz= fkBdcThYc14_bGX8tLrTqaBWq2zfgNUuiu4ZXjlO1Lqrbu0$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6BmdBjzrvzZaLaHp8zCQZ7JGjrw4Jes_1WFV64-MspDz= fkBdcThYc14_bGX8tLrTqaBWq2zfgNUuiu4ZXjlO5NL9ldo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6BmdBjzrvzZaLaHp8zCQZ7JGjrw4Jes_1WFV64-MspDz= fkBdcThYc14_bGX8tLrTqaBWq2zfgNUuiu4ZXjlOPkuu2oo$=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) .