Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Oct 02 2023 00:46:11 FOUS30 KWBC 020046 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 844 PM EDT Sun Oct 01 2023 Day 1 Valid 01Z Mon Oct 02 2023 - 12Z Mon Oct 02 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS SOUTHEAST PORTIONS OF THE FLORIDA PENINSULA... ....Florida Peninsula... 0100 UTC Update -- Based on the latest observational and mesoanalysis trends, along with recent HRRR and HREF runs, have curtailed the northern portions of the Slight Risk out of the Space Coast and much of the Treasure Coast. 18Z HREF exceedance probabilities for the overnight (>1-2"/hr rates and >3"/12 hrs between 00-12Z) are not as robust compared to last night-early this morning, however are sufficient to maintain a Slight Risk across SE FL along and ahead of the front, especially given the current trends/more numerous cells. ....New Mexico/West Texas and western portions of the Oklahoma Panhandle... 0100 UTC Update -- Based on the latest convective trends (satellite/radar/mesoanalysis), along with the recent HRRRs and 18Z HREF exceedance probabilities, have expanded the Marginal Risk to include the remaining portion of southeast and south-central NM and much of West TX. Expanding thunderstorm coverage with periods of training will maintain an isolated flash flood threat across eastern NM into portions of western TX through 05Z. Rainfall rates of 1-2"/hr will be possible in isolated areas. For further information, please refer to the latest mesoscale precipitation discussion or MPD #1122, which is in effect until 0530 UTC. Hurley Day 2 Valid 12Z Mon Oct 02 2023 - 12Z Tue Oct 03 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHERN HIGH PLAINS OF NEW MEXICO AND TEXAS... ....20Z Update... ....Southern High Plains... No major changes were made to the ERO risk areas for Day 2/Monday. The Slight Risk remains in place for eastern NM and portions of the TX Panhandle as a deep trough ejects out of the Rockies, which when added to increasing Gulf moisture ahead of the trough will result in widespread shower and thunderstorm development in the Slight Risk area. Training will be the primary concern as the storms largely struggle to move east, instead tracking NNE to NE. Expect heavy rainfall rates as high as 2 inches per hour with the strongest storms. NASA Sport imagery shows the area is at to a bit below normal as far as soil moisture conditions go, so it will likely take multiple rounds of storms to result in widely scattered flash flooding except where any bigger towns or flood sensitive areas are hit with the heavier rains. ....Florida... The front over the center of the Peninsula now will make its way to the southern tip of the state by Monday/Day 2. Predominantly easterly flow will allow for a renewed round of convection in the Miami-Ft. Lauderdale area, and as with the past few days will be slow moving and moisture-laden. Thus, the threat for flash flooding remains in the urban areas predominantly. Out over the Everglades it's much more difficult for heavy rains to result in flash flooding, so the Marginal Risk area was trimmed from the west to highlight the greatest threat being in the urban areas. For the Keys, any excessive rainfall induced flooding would likely be compounded by tidal flooding. Wegman ....Previous Discussion... ....Southern High Plains of New Mexico and Texas... Confidence has increased enough to warrant an upgrade of the New Mexico/west Texas Marginal to a Slight Risk. The Southern High Plains will be under the influence of deep diffluent flow from a potent upper trough propagating through the West on Monday. This will be coupled with the arrival of a strong upper jet aloft and favorable low level jet dynamics. Cape values in the 1000-1500J/Kg range and moisture anomalies well over 2 standard deviations (1-1.5in") should support thunderstorm activity (some severe) with excessive rainfall potential. ....Florida... Albeit weaker than today's threat, Monday's heavy rainfall threat will shift to southern Florida as the surface front, which will continue to be the focus for storms, shifts southward. Instability will weaken on Monday so any excessive rainfall threats will likely be few and far between. The main threat from potential heavy rainfall will be over urban areas. Kebede Day 3 Valid 12Z Tue Oct 03 2023 - 12Z Wed Oct 04 2023 ,...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE GREAT PLAINS AND THE EAST COAST OF FLORIDA... ....20Z Update... Once again no major changes were made to the inherited forecast. Over the Plains, the Marginal Risk area looks good for the uncertainty as to where the strongest storms will develop. The overall area was nudged a row of counties east, and trimmed on the western side, particularly across western SD, where the center of the low is expected to track, which will end the rainfall threat more quickly. More of ND may be able to be trimmed with future updates due to lack of instability on the northern side of the low, but the confidence wasn't quite there to make that change. ....Florida... An easterly wave is expected to move into the Space Coast Tuesday and especially Tuesday night. This area has been hard-hit with rainfall the past few days, and so while the rainfall forecast at this point is meager along the coast, there remains some chance that slow-moving/training storms could cause localized flash flooding, especially right along the coast. This is a low-confidence Marginal, and any bigger changes in frontal position could result in bigger changes to the Marginal Risk area. Wegman ....Previous Discussion... A rapidly developing mid-latitude cyclone, supported by a deep upper-level trough will produce thunderstorms (some severe) and moderate to heavy rainfall across the Great Plains on Tuesday. Confidence has diminished a bit since the last issuance regarding excessive rainfall over parts of the Northern Plains, therefore the Slight Risk has been removed. The broad Marginal area remains due to the potential for excessive rainfall, particularly over parts of the Central Plains where favorable instability within potential severe storms could enhance rainfall rates. PWATs will be well over 1 inch across the Plains on Tuesday with impressive low level winds. Kebede Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8smlfaH_zHr23zKJxBxku_tpvcqX1K5_nMpSBu6kc5bN= EI8o5M60dLowo2pcwPltPdtIoow7HqTsJq8piLAejqF2qDY$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8smlfaH_zHr23zKJxBxku_tpvcqX1K5_nMpSBu6kc5bN= EI8o5M60dLowo2pcwPltPdtIoow7HqTsJq8piLAeVbt6KJM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8smlfaH_zHr23zKJxBxku_tpvcqX1K5_nMpSBu6kc5bN= EI8o5M60dLowo2pcwPltPdtIoow7HqTsJq8piLAeudD2aJo$=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) .