Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Feb 15 2024 00:16:53 FOUS30 KWBC 150016 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 715 PM EST Wed Feb 14 2024 Day 1 Valid 16Z Wed Feb 14 2024 - 12Z Thu Feb 15 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Hurley =20 Day 2 Valid 12Z Thu Feb 15 2024 - 12Z Fri Feb 16 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. ....21Z Update... The previous forecast reasoning still holds, and a blank Day 2 ERO was maintained with the afternoon forecast cycle. With a lack of surface forcing and instability, it will be hard to get rain rates high enough to cause flash flooding in South Texas, a region that has been relatively dry and has high flash flood guidance. Most hi-res guidance shows 24 hour precipitation totals reaching 2-3 inches at most with rainfall rates likely remaining below an inch per hour. The HRRR is more aggressive with QPF due to stronger convergence across South Texas Bush Country, but still just barely reaches totals near floash flood guidance. Kleebauer/Dolan ....Previous Discussion... Lower Rio Grande Valley of Southern TX... Low level moisture will return ahead of a shortwave trough in the southern stream...with precipitable water vales increasing into the 1.5 to 2.0 inch range across southern Texas by 12Z on Friday. The problem continues to be the lack of a low level boundary. Guidance is still able to generate some convection across parts of the Lower Rio Grande Valley with maximum QPF generally in the 1.5 to 2.5 inch range. Relatively dry antecedant conditions combined with a lack of better instability should limit any flooding potential. The area will continue to be monitored for changes with future forecast cycles. Otto/Bann Day 3 Valid 12Z Fri Feb 16 2024 - 12Z Sat Feb 17 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. ....21Z Update... After coordination with the Brownsville and Corpus Christi WFOs, the Marginal Risk area along the Lower Texas Coast was removed from the Day 3 ERO. There is a large amount of spread in QPF totals amongst models, but most ensemble means and deterministic runs continue to show totals only near 1-2 inches with locally higher amounts possible. The coastal plains of Texas would be able to handle this amount of rainfall with only nuisance flooding in urban and poor drainage areas. The forecast could change depending on the placement of the developing surface low. If the low remains removed from the coast over the western Gulf with accompanying instability gradient, then the highest precipitation totals will likely focus over the Gulf. However, if the low develops right along the Lower Texas Coast, then the higher amounts could shift over the coastal plain and potentially cause isolated flooding concerns, especially within the urban centers like Corpus up to Victoria. This area will continue to be monitored as the forecast updates/changes over the next couple days. Kleebauer/Dolan ....Previous Discussion... Continued amplification of the wave at mid-levels over northern Mexico during the period will push a cold front into the southern part of Texas and support showery conditions. The expectation is that a surface low will develop over portions of the western Gulf of Mexico and eventually focus the heavy rainfall away from land.=20 Until that happens...deep moisture will be in place with precipitable water values in excess of 1.6 inches / some 2 to 3 standardized anomalies above climatology for this time of the year / with generally modest low level moisture transport into the region. Given that deterministic QPF is on the order of an inch or two...and the antecedent have been dry over an area of primarily agricultural land usage...it would appear that much of the area could handle the rain with limited exceptions in regions of poor drainage or in urban areas. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6Vs8YjVvMK7tnWO3xqYwpmxtzSN40KVnJistA-JGsEJF= eqcrI8k1Xl57ao65uDpMf5F11W2PUZWJJStdFEVWst3LI4U$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6Vs8YjVvMK7tnWO3xqYwpmxtzSN40KVnJistA-JGsEJF= eqcrI8k1Xl57ao65uDpMf5F11W2PUZWJJStdFEVWqOZSfQI$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6Vs8YjVvMK7tnWO3xqYwpmxtzSN40KVnJistA-JGsEJF= eqcrI8k1Xl57ao65uDpMf5F11W2PUZWJJStdFEVWxlvvEB8$=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) .