Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Mar 16 2024 07:38:44 FOUS30 KWBC 160738 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 338 AM EDT Sat Mar 16 2024 Day 1 Valid 12Z Sat Mar 16 2024 - 12Z Sun Mar 17 2024 ....A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS IN AND NEAR SOUTH- CENTRAL AND SOUTHEAST TEXAS... Difluence aloft ahead of an upper level low moving slowly across=20 Arizona teams up with a quasi-stationary front to continue the=20 potential for heavy rainfall in the front's vicinity. The guidance=20 has shifted northward when compared to this time yesterday, which=20 led to a similar shift in the Slight Risk area. Slight warming in=20 the temperatures at 700 hPa imply that the heavy rain threat should edge northward, which appears to be beginning per recent radar=20 reflectivity trends in southeast TX, but how far north remains the question. Inflow at 850 hPa from the Gulf should pulse up to 25-30 kts at times, importing ML/MU CAPE of 2000 J/kg or so. Effective=20 bulk shear should be sufficient for organized convection, capable=20 of producing hourly rain totals to 2" and local amounts to 4". The=20 guidance indicates a couple rounds of convection this period, early and late. Dispersion continues concerning where within southern and eastern TX the heavy rainfall is most likely to occur, but the=20 amounts still appear high enough to maintain the Slight Risk threat in the outlook. There was some accounting for the heavy rainfall=20 that fell on Friday near the southern border of LA/TX in helping to define the eastern edge of the Slight Risk area. Roth Day 2 Valid 12Z Sun Mar 17 2024 - 12Z Mon Mar 18 2024 ....A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS NEAR THE SOUTHERN LOUISIANA/TEXAS BORDER... Organized convection in the vicinity of a front, which should be=20 somewhere the southern border of TX/LA Sunday morning, is expected to lead to heavy rainfall for portions of the northern Gulf coast. Sufficient 850 hPa inflow off of the Gulf of Mexico, up to 40 kts, will lure precipitable water values of 1.5-1.75" into the region=20 and MU CAPE up to 2000 J/kg. Difluence aloft should be fostered by=20 increasing troughing across the Great Lakes, Midwest, and=20 Mississippi Valley. There is some signal in the guidance for=20 cooling temperatures at 700 hPa, which is of concern as the=20 1000-500 hPa thickness diffluence is now very close to the LA=20 coast. This means that there is some chance that organized=20 convection could shift slightly offshore LA at some point in its=20 evolution, leading to decreasing confidence in heavy rainfall the farther east you go in LA. Both the 00z NAM and 12z-00z ECMWF are=20 on the north side of the guidance envelope (which usually isn't=20 good news for the ECMWF solution) while the remainder of the=20 guidance lies closer to the Gulf coast, including the normally=20 northward- biased 00z UKMET. The guidance shows a bit of=20 progression to the convective pattern, as an upper trough sharpens=20 across the Ohio and Mississippi Valleys and helps act to shift the=20 moisture plume/best 850 hPa inflow east with time. Hourly rain=20 totals to 2.5" with local amounts to 4" are possible where limited=20 cell training occurs and/or mesocyclones happen to develop. Because of the heavy rainfall that occurred on Friday near the southern=20 TX/LA border, and per coordination with the LCH/Lake Charles LA=20 forecast office, added a targeted Slight Risk area to areas where=20 soils recently became more sensitive. Roth Day 3 Valid 12Z Mon Mar 18 2024 - 12Z Tue Mar 19 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Roth Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8camMbG3zPaA-QrPasJZOKqhBKY76Xwl32j4H9JoxwIt= qtu1qOE_gdmyvu52P-_7POCtm0E2OzDTXBPMUAV1bAAD11U$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8camMbG3zPaA-QrPasJZOKqhBKY76Xwl32j4H9JoxwIt= qtu1qOE_gdmyvu52P-_7POCtm0E2OzDTXBPMUAV19rs7AaU$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8camMbG3zPaA-QrPasJZOKqhBKY76Xwl32j4H9JoxwIt= qtu1qOE_gdmyvu52P-_7POCtm0E2OzDTXBPMUAV1eDY4JDI$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .