Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Apr 01 2023 19:39:47 FOUS30 KWBC 011939 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 338 PM 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 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF NORTHEAST TEXAS INTO THE LOWER MISSISSIPPI VALLEY... The closed low over southern CA (as of 18z Sat) will track into the Southern Plains on Sunday and be responsible for an area of organized convection Sunday afternoon and night. Model agreement in the overall synoptic setup is pretty high. The aforementioned mid level shortwave combined with an upper jet to the north will provide the large scale ascent. This forcing will interact with a lifting warm front, with upwards of 40 kts of 850mb flow resulting in pretty good moisture transport/convergence and PWs around the climatological 90th percentile. QPF differences amongst the models are most likely mainly driven by different handling of the convective evolution. Cells will form Sunday afternoon over portions of northeast TX into southeast OK, and should evolve into an organized area of convection fairly quickly. Mean wind fields would suggest an east northeastward progression of this convection. However as convection organizes it should tend to build into the low level jet and track along the instability gradient. This would support more of a east southeast and eventual southeast progression of the most intense convection. Corfidi vectors and thickness lines also support this east southeast to southeast movement. For this reason we continue to lean away from the guidance that has more of a east to northeast progression of the heaviest rainfall. Guidance such as the 12z HRRR, ARW and Gem Reg seem to have the more realistic evolution based on these thoughts. The system as a whole will be progressive, limiting the higher end QPF/flood potential. However some east to west training seems reasonable given the broad moisture transport along the warm front, and this scenario is supported by some of the 12z HREF members. It seems likely that we will see a swath of 2-4" of rain somewhere from northeast TX towards the AR/LA border and into central MS, although at the moment 5"+ probs from the HREF are zero (indicative of the upper bound cap due to the progressiveness of the system). Still think this supports an isolated to scattered flash flood risk, so the Slight risk will be maintained. The area was adjusted a bit north over northeast TX, and then south over MS to account for the aforementioned expected east southeast movement of stronger convection. Chenard Day 3 The Day 3 outlook will be updated by 2030Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-1qjkyWbm8o2e8DzTbkRfzTuuHhLqQ1OSJvVHiLcDBq9= kxFR9ZVOLtHWmt6ITWtI12Qb3TUMiDEJCywMuST4Jb9t3mA$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-1qjkyWbm8o2e8DzTbkRfzTuuHhLqQ1OSJvVHiLcDBq9= kxFR9ZVOLtHWmt6ITWtI12Qb3TUMiDEJCywMuST4E02QVU8$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-1qjkyWbm8o2e8DzTbkRfzTuuHhLqQ1OSJvVHiLcDBq9= kxFR9ZVOLtHWmt6ITWtI12Qb3TUMiDEJCywMuST4hT9fLWA$=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) .