Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Apr 01 2023 07:24:41 FOUS30 KWBC 010724 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 323 AM EDT Sat Apr 01 2023 Day 1 Valid 12Z Sat Apr 01 2023 - 12Z Sun Apr 02 2023 Deep convective activity is expected to be most robust but generally progressive Saturday morning along the southern edge of a departing deep layer cyclone moving from the Great Lakes into New England. The best overlap of available moisture and instability that shows persistence is in the vicinity of the AL/GA/FL border junction. There's a bit of dispersion in the 00z QPF guidance in this region, but an inspection of one of the instability fields from the 00z GFS suggests that the mesoscale guidance/HREF are on to something regarding the highest chances (which are low) of 2"+ being across portions of the FL Panhandle, FL Big Bend, and portions of southern AL and southern GA. The 0-100 cm moisture is telling, showing a dry patch across south-central GA which allowed their removal from the Marginal Risk area. To the north across the Carolinas, the front is more progressive and moves through right as the instability is increasing. The moisture isn't overly stellar in the Carolinas either, generally below 1.5". Coordination with CHS, CAE, and ILM led to the removal of the Marginal Risk area in those regions.=20 Some 1-2" totals may occur over a relatively short period, with the FL Panhandle and surroundings most likely to experience isolated/ localized training along the tail end of a cold front.=20 Cell mergers and mesocyclones cannot be ruled out. The rapid movement of the convection will likely limit the potential for flash flooding to isolated areas.=20=20 Roth 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!9ITUovihseyQzrw1v97ZktyVk_tsJv0kENHg_aJBexfS= PG2YFiYgdR03RYmc-DMQ6uTepnGFdTsWym5KF20607gPu_g$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9ITUovihseyQzrw1v97ZktyVk_tsJv0kENHg_aJBexfS= PG2YFiYgdR03RYmc-DMQ6uTepnGFdTsWym5KF206WYtt32Q$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9ITUovihseyQzrw1v97ZktyVk_tsJv0kENHg_aJBexfS= PG2YFiYgdR03RYmc-DMQ6uTepnGFdTsWym5KF206fCO3xto$=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) .