Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Oct 04 2024 19:35:55 FOUS30 KWBC 041935 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 335 PM EDT Fri Oct 4 2024 Day 1 Valid 16Z Fri Oct 04 2024 - 12Z Sat Oct 05 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Coastal trough with an embedded surface low will settle just off the TX coast with prevailing northeast flow centered from CRP down to BRO. This will aid in advection of elevated moisture with PWATs jumping >2" by this afternoon leading to a bit more environment moisture to work with for locally heavy rain opportunities. There's still a sharp gradient within the theta-E alignment with the best instability axis located directly along the coast and out into the neighboring Gulf. The setup is borderline conducive for heavier totals, but mainly confined to that immediate coastal plain where the convective pattern is likely to settle. Considering the very high FFG's located within the zone of interest, the main threat will be relegated to the urban zones like Brownsville to perhaps Harlingen, but even that far inland might be a stretch. The current probabilities are inflated due to two CAMs members already insinuating a heavy rain footprint overhead with more to come. The radar is not in agreement and the 12z HRRR has the best handle amongst the CAMs this morning, and that signal is fairly meager for a flash flood threat. Will continue with the non-zero wording, but will remain very localized for flash flood concerns, if any occur, and not within the 5% threshold necessary for a risk area addition. A nil ERO will be maintained across the CONUS as a result. Kleebauer Day 2 Valid 12Z Sat Oct 05 2024 - 12Z Sun Oct 06 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR COASTAL DEEP SOUTH TEXAS... A lingering coastal trough will remain parked off the South TX coast with a prevailing northeasterly flow pattern situated from South Matagorda Bay down into the Lower RGV with elevated PWATs situated along the coastal plain. The combination of marginal instability and improving deep layer moisture will present an opportunity for scattered to numerous convective cells pivoting onshore from the adjacent Gulf. Current neighborhood probs for >3" are very elevated (60-80%) over the course the D2 time frame with=20 a majority of the precip falling in the first 6-8 hrs of the period before slowly waning. The 12-15 hour period from the end of D1 through the first half of D2 is signaling locally upwards of 5-7" in the hardest hit locations with the accumulating factor of=20 precip from period to period relating to the flash flood chances as we move into D2. In coordination with the local WFO BRO in South=20 TX, a targeted MRGL risk was added across the coastal portions of=20 the region, including parts of Kenedy, Willacy and Cameron=20 counties.=20 Kleebauer=20 Day 3 Valid 12Z Sun Oct 06 2024 - 12Z Mon Oct 07 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE SOUTH FLORIDA PENINSULA... A broad expanse of elevated moisture within a disheveled tropical wave/trough axis over the Gulf will migrate eastward towards the FL Peninsula by later Sunday with an increasing heavy rain threat situated over the Southwest coast of FL, expanding eastward over the Everglades and eventually the metro corridor in Southeast FL. Recent trends within both deterministic and ensembles have increased areal coverage of 2+" precip potential to include now both coasts within South FL with the precip maximum creeping closer to 4" locally as we move forward with time. The prospects of flash flooding will only look to increase so long as the trend remains and the CAMs begin noting heavier pockets of precip as we introduce better convectively allowing physics into the setup. Recent ECMWF AIFS ML output pinpoints the introduction of heavier rain across=20 the above area allowing for heightened confidence for the threat.=20 FFG indices will remain high just given the regions impacted, but=20 the urban setting will still be present for the greatest expected=20 impacts during the period. The previous MRGL risk was maintained,=20 but in coordination with the Miami WFO, the risk was expanded to=20 include the metro corridor on the opposite coast up to just south=20 of Lake Okeechobee. Kleebauer=20 Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_XNJoeln7YG9pCZ3OlMTD3CjlQ_6QqsB5KfK_tlIDQcB= 6GooA4efMLWZzQq862Di14Y56_GjuKiPlaeztRF37R69HwA$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_XNJoeln7YG9pCZ3OlMTD3CjlQ_6QqsB5KfK_tlIDQcB= 6GooA4efMLWZzQq862Di14Y56_GjuKiPlaeztRF30zbjU1c$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_XNJoeln7YG9pCZ3OlMTD3CjlQ_6QqsB5KfK_tlIDQcB= 6GooA4efMLWZzQq862Di14Y56_GjuKiPlaeztRF3K3ERTkw$=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) .