Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Feb 09 2023 15:53:22 FOUS30 KWBC 091553 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1052 AM EST Thu Feb 09 2023 Day 1 Valid 16Z Thu Feb 09 2023 - 12Z Fri Feb 10 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE WESTERN FLORIDA PANHANDLE, SOUTHERN ALABAMA, AND SOUTHWESTERN GEORGIA... A Marginal Risk of excessive rainfall has been maintained for the western FL Panhandle, southern AL, and portions of southwestern GA for the updated Day 1 ERO, due to a stalling cold front moving into the region this morning. The only meaningful change from the prior issuance was to shrink the northern and western extent of the Marginal as precipitation from this morning slides eastward. Precipitable water values ahead of the front values currently range from 1.4-1.6 inches (well above the 90th percentile per TLH sounding climatology), with sufficient instability (MUCAPE of 250-750 J/kg, per the HREF mean) suggesting that rainfall rates may locally approach 2"/hr at times. There is also the possibility of repeating rounds of heavy rainfall, given the stalling of the trailing front (with HREF 3" neighborhood exceedance probabilities as high as 20-30% over the western FL Panhandle). However, antecedent soil conditions in the region are quite dry, with NASA SPoRT 0-40 cm soil moisture values indicated to be as low as the 10-20th percentile. This should significantly limit the areal extent of any flash flooding, along with the fact that any 3" exceedance will likely occur over a period of longer than 6 hours. Nevertheless, poor drainage/urban areas will be the most at risk of realizing any isolated flooding impacts. It's also worth noting that the amount of rainfall that ultimately occurs today will have important implications for Friday and Saturday, as the FL Panhandle and surrounding portions of AL/GA may see many additional rounds of locally heavy rainfall going into the weekend. Churchill/Snell Day 2 Valid 12Z Fri Feb 10 2023 - 12Z Sat Feb 11 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE WESTERN FLORIDA PANHANDLE, SOUTHERN ALABAMA, AND WESTERN GEORGIA... A stalling frontal zone is expected to result in a lingering axis of significant tropospheric moisture (precipitable water values of 1.3-1.6 inches, above the 90th percentile climatologically) from the FL Panhandle and southern AL northeastward into south-central GA, SC, and southeastern NC on Friday and into Friday night. Despite the presence of these anomalously high PWATs, large-scale lift is still expected to remain fairly limited (as the aforementioned upper-low slowly digs south into the far western Gulf) with very little instability expected (generally less than 250 J/kg of MU CAPE, but near 500 J/kg in the vicinity of the FL/GA border per the HREF mean). Thus a fairly narrow Marginal Risk area was maintained, with rainfall totals generally expected to range from 1-2 inches across the area (with localized higher amounts possible due to the potential for training cells across the stalling frontal zone). Given the relatively dry antecedent conditions and already limited potential for rainfall to exceed the high FFG, any instances of flash flooding are expected to remain isolated and primarily confined to areas of poor drainage. Churchill Day 3 Valid 12Z Sat Feb 11 2023 - 12Z Sun Feb 12 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF NORTH CAROLINA, SOUTH CAROLINA, GEORGIA, EASTERN ALABAMA, AND NORTHERN FLORIDA... An upper-level cut-off low is expected to meander east-northeastward across the Southeastern states on Saturday, dropping 1-3 inches of rainfall and resulting in at least a Marginal Risk of excessive rainfall from northern Florida through Georgia, eastern Alabama, South Carolina, and much of North Carolina. Despite the expected lack of instability (GFS MU CAPE near 0 J/kg), tropospheric moisture levels are expected to remain very elevated, with precipitable water values ranging from 1.25-1.75 inches (at or above the 90th percentile climatologically) with large-scale lift provided from the traversal of the upper-low (and expected surface cyclogenesis). A possible Slight Risk area has yet to be identified, as the exact track of the upper-level low (and eventual surface low) will play a crucial role in determining the specifics of the rainfall amounts and associated impacts. Dry antecedent conditions are also preceding this system, and rainfall amounts on both Thursday and Friday will be crucial in determining where a Slight Risk will ultimately be introduced. Regardless, this system will bring a continued threat for isolated flash flooding (at a minimum), particularly across urban terrain and poor drainage areas. Churchill Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4k73EUdknAk5Az5qlAS5og9jGXZZw1TGC-Isd_YwrjAQ= i_yIKmRmWY8IYsEWTP3IEd85zBd0CO7gblvXLHkysF9HSoM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4k73EUdknAk5Az5qlAS5og9jGXZZw1TGC-Isd_YwrjAQ= i_yIKmRmWY8IYsEWTP3IEd85zBd0CO7gblvXLHky9q3S84E$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4k73EUdknAk5Az5qlAS5og9jGXZZw1TGC-Isd_YwrjAQ= i_yIKmRmWY8IYsEWTP3IEd85zBd0CO7gblvXLHkyrV1fI9s$=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) .