Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Oct 13 2024 00:16:56 FOUS30 KWBC 130016 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 816 PM EDT Sat Oct 12 2024 Day 1 Valid 01Z Sun Oct 13 2024 - 12Z Sun Oct 13 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF=20 THE UPPER FLORIDA KEYS & THE FLORIDA GOLD COAST... Satellite and radar imagery have shown shower and occasional thunderstorm activity moistening the column in the mid and upper levels of the troposphere ahead of a shortwave moving through the eastern Gulf of Mexico/FL Panhandle. This moistening trend is apparent both of water vapor imagery and trends in the MFL upper air sounding over the past 24 hours. The overall synoptic pattern=20 favors slow-moving convective cells along and near the Gold Coast=20 given easterly low level flow and westerly upper level winds, with the MFL sounding showing strong veering between the surface and ~600 hPa/15,000 feet. While the mesoscale guidance indicates that=20 the heaviest rainfall is expected just offshore, VAD wind profiles=20 from the MIA, FLL, and PBI terminals show slightly stronger flow at 850 hPa than indicated in 22z RAP mass fields to the northeast of=20 a circulation west of FL Bay and offshore southwest FL. This=20 appears to indicate a better chance of activity moving ashore,=20 particularly at or past 06z. After coordinating with MFL/the Miami=20 FL forecast office, went ahead and raised the threat level to a=20 Slight. The ingredients in place support the potential for a localized=20 higher end flash flood event somewhere within South FL tonight, particularly coastal Miami-Dade and Broward counties. Precipitable water values are ~2.25" and effective bulk shear is 30-40 kts. ML=20 CAPE is mostly 250-500 J/kg except in southern Miami-Dade, but RAP=20 guidance does show a 500+ J/kg uptick overnight. Both quasi-=20 stationary thunderstorms and random mesocyclones are the expected=20 heavy rain threats, with the possibility of 3" an hour totals and=20 local amounts around 6" should activity move ashore and any areas=20 see a couple hours of issues before showers and storms reorient, as they typically do as instability exhausts overland. Weekly=20 rainfall have been 200-600% of average, so the area is fairly=20 saturated. While confidence isn't high, raising to a Slight Risk=20 appears to be the course of least regret. Roth Day 2 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 Sunday is a continuation of today's threat over Southeast Florida. The overall thermodynamic ingredients remain similar, however there is still spread with the mesoscale to synoptic setup. The 12/12Z GFS and 12/12Z ECMWF have trended quicker with the weak wave and suggest the better organized convective risk will now be offshore and over the Bahamas. However the GEM and some HREF members are on the slower side and focus more convection over south Florida. The uncertainty in these details continues to be too large to go with anything more than a Marginal risk at this time. Overall the signals in the models suggest the flood risk on Sunday is trending downward but lingering amounts of moisture and instability parameters suggest at least a localized flash flood risk could persist. Bann Day 3 Valid 12Z Mon Oct 14 2024 - 12Z Tue Oct 15 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!93NwHjZo8zjkIKwi0fsBEkUhgSbEDD4IV_KMuvgJJWPT= gGhKsyTPm658bLJo4TM0DF6mcoOOtFB__jMs-iXr6iZ-5UU$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!93NwHjZo8zjkIKwi0fsBEkUhgSbEDD4IV_KMuvgJJWPT= gGhKsyTPm658bLJo4TM0DF6mcoOOtFB__jMs-iXrAha2KRY$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!93NwHjZo8zjkIKwi0fsBEkUhgSbEDD4IV_KMuvgJJWPT= gGhKsyTPm658bLJo4TM0DF6mcoOOtFB__jMs-iXrujBvDpQ$=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) .