Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Feb 18 2024 08:27:38 FOUS30 KWBC 180827 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 326 AM EST Sun Feb 18 2024 Day 1 Valid 12Z Sun Feb 18 2024 - 12Z Mon Feb 19 2024 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SANTA LUCIA AND SANTA YNEZ RANGES IN CENTRAL/SOUTHERN CALIFORNIA... ....California... A second stronger system is expected to bring another round of heavy rainfall to portions of CA today. This will be a larger scale trough with a much broader IVT plume directed into CA...thus the latitudinal coverage of rainfall will be quite large with several areas of concern for potential flooding. A Moderate risk remains for the Santa Ynez range in Santa Barbara county, and it was expanded northward into the Santa Lucia range from San Luis Obispo into Monterey counties. This is the corridor where the heaviest rainfall is expected through 12z Monday, with the heavier rates first impacting the Santa Lucia range by 00z, and then shifting southward into the Santa Ynez between 06z-12z Monday. By 12z Monday 00z HREF guidance supports 5"+ amounts over the Santa Lucia and 3"+ amounts over the Santa Ynez (with more to come here after 12z). Initially this rainfall will be driven by increasing IVT oriented perpendicular to the terrain, which will support a steady moderate rainfall, but limited instability should keep rainfall rates from getting too high. However with time some weak instability will try to work into the area from north to south near and just ahead of the cold front. This should result in an uptick in rainfall rates...with 00z HREF data showing over a 70% chance of 0.75"/hr rainfall over the Santa Lucia range. This should be enough to result in some areas of significant flooding.=20 The broad Slight risk over the central/northern CA coast into portions of the Sacramento and San Joaquin valley and into the western slopes of the Sierra remains mainly unchanged. Rainfall will move into coastal areas by 21z, and then spread inland thereafter. The IVT axis is expected to make good inland progress, and may actually slow/stall over portions of the Sacramento and northern San Joaquin valleys. To go along with this IVT and convergence axis, upper level flow is forecast to be very divergent within the left exit region of a strong jet. This combination should result in heavy rainfall over these valley locations, with some weak instability also forecast supporting some embedded convective elements and potential localized 0.5"/hr rainfall. The best potential for these higher rates and flash flooding should be between 00z and 12z when steeper lapse rates overrun the moisture plume. This event could end up resulting in both longer duration flooding from the multi round event, and also more rapid response flash flooding given the aforementioned higher rate potential tonight into Monday morning. With high snow levels, some flooding impacts are also possible even in portions of the central/northern Sierra and spilling over into the eastern foothills/valley locations. ....Florida... A Marginal risk was maintained across portions of the east central and southeast FL coast. Plenty of forcing and moisture for heavy rainfall with an approaching mid level trough, strong upper jet and PW values over the climatological 95th percentile. However instability will again be a limiting factor for flash flooding for the central and northern portions of the state. However a warm or stationary front over southern FL will result in some added low level convergence and some pooling of instability there. High res guidance indicates upwards of 1000 j/kg of CAPE over south FL near and south of this front which will be enough to support some heavier rainfall rates and some flash flood risk. The expectation is that an area of organized convection will move across south FL today, dropping a swath of as much as 3-5" of rain from near Naples to Palm Beach and points south. While hourly rainfall of 1-2"/hr is probable with this activity, even the high QPF from the 06z HRRR is barely getting to 50% of FFG. Thus still thinking any flooding will be localized and confined to any more sensitive urban areas. Chenard Day 2 The Day 2 outlook will be updated by 0830Z. Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7o_4YUZwewDmva76OCWLrxKdmbGXhrxKa_Gm7Iw1jTc7= HvNgZUbBlYGV-nrJtmfhi21q98xXZM_DxZHtsnbBD9WPAoo$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7o_4YUZwewDmva76OCWLrxKdmbGXhrxKa_Gm7Iw1jTc7= HvNgZUbBlYGV-nrJtmfhi21q98xXZM_DxZHtsnbBpLQytfA$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7o_4YUZwewDmva76OCWLrxKdmbGXhrxKa_Gm7Iw1jTc7= HvNgZUbBlYGV-nrJtmfhi21q98xXZM_DxZHtsnbBBHvhs7s$=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) .