Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Oct 11 2024 15:55:40 FOUS30 KWBC 111555 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1155 AM EDT Fri Oct 11 2024 Day 1 Valid 16Z Fri Oct 11 2024 - 12Z Sat Oct 12 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Easterly low level flow will bring showery conditions to the central and southeast Atlantic coast of FL from this afternoon into tonight. 12Z soundings showed precipitable water values at or below 1.5 inches that resulted in limited instability. That...combined with a relative lack of organization shown currently on satellite or in the short-range hi-resolution guidance...suggests that=20 rainfall rates or totals are not likely to reach levels of concern=20 for flash flooding. Thus we will continue to carry no risk area in=20 the ERO. Bann Day 2 Valid 12Z Sat Oct 12 2024 - 12Z Sun Oct 13 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE UPPER FLORIDA KEYS INTO THE SOUTHEAST FLORIDA URBAN CORRIDOR... Moisture and instability return northward into southern FL Saturday into Saturday night, with PWs increasing towards 2.25" and CAPE over 1000 j/kg. Meanwhile a weak wave moving into the eastern Gulf of Mexico may result in an uptick in low level flow and convergence. Thus expect we should gradually see an uptick in convective coverage this weekend over the Keys into south FL. Easterly low level flow and westerly upper level winds support the potential for slow moving convective cells near the coastal convergence axis. Timing remains a bit uncertain, and the better convective coverage may end up more over the Keys this period (where flash flooding is harder to come by), but given the increasing moisture and instability there is at least a conditional threat of localized flash flooding Saturday into Saturday night into the more urban areas of southeast FL. If deep convection does indeed develop then urban flash flooding is possible from the upper Keys into southeast FL. Chenard Day 3 Valid 12Z Sun Oct 13 2024 - 12Z Mon Oct 14 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE UPPER FLORIDA KEYS INTO THE SOUTHEAST FLORIDA URBAN CORRIDOR... The risk on day 3 is a continuation of the threat on day 2 over Southeast FL. The overall thermodynamic ingredients remain the same, however there is a chance that forcing will be stronger by Sunday. Still some timing and positional differences amongst the guidance, but the general consensus is for a weak wave to move across FL Sunday, which should both result in a subtle uptick in mid/upper forcing and locally enhance lower level convergence. Thus currently expecting a greater chance of loosely organized convective clusters Sunday into Sunday night...and with wind fields still supporting slow moving cells...this activity could tend to anchor along the coastal convergence axis for a while. Thus isolated urban flash flooding is considered possible. Certainly a chance that a Slight risk may be needed for one of these weekend days...but given some uncertainty with the synoptic evolution and convective coverage, think a good first step is just introducing Marginal risks for both days 2 and 3 (Sat and Sun) and continue to monitor trends. Chenard Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4GQcszuBbHTQqUV-JZm2WCZ8s-U2vWpzu3SCAiPhS7jf= r8GDsRzRyDXn-NgoVyCfBWPRKNUhl6ZI1Y_PCJA-Bd2kRI8$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4GQcszuBbHTQqUV-JZm2WCZ8s-U2vWpzu3SCAiPhS7jf= r8GDsRzRyDXn-NgoVyCfBWPRKNUhl6ZI1Y_PCJA-PoDVF8o$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4GQcszuBbHTQqUV-JZm2WCZ8s-U2vWpzu3SCAiPhS7jf= r8GDsRzRyDXn-NgoVyCfBWPRKNUhl6ZI1Y_PCJA-Sp6s6VM$=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) .