Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jan 29 2025 00:13:33 FOUS30 KWBC 290012 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 712 PM EST Tue Jan 28 2025 Day 1 Valid 01Z Wed Jan 29 2025 - 12Z Wed Jan 29 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Bann Day 2 Valid 12Z Wed Jan 29 2025 - 12Z Thu Jan 30 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF NORTH TEXAS AND SOUTHERN OKLAHOMA... ....1930 UTC Update... Minimal changes made to the Day 2 ERO Marginal Risk area across North TX into eastern OK and western AR -- mainly to push the leading (eastern) edge of the outlook area a little farther east, based on the latest guidance/trends. Hurley ....Discussion... An upper level cutoff low ejecting out of the Southwest into the Plains will provide forcing for ascent for a developing low over the Texas and Oklahoma Panhandles Wednesday and Wednesday night. Return flow of Gulf moisture, warmth, and instability ahead of the low will advect north across Texas and into Oklahoma and Arkansas Wednesday and especially Wednesday night. The typical diurnal strengthening of the LLJ Wednesday night will greatly increase the coverage and intensity of storms along the developing low's cold front across Texas, while the warm front locally increases lift into Oklahoma. The surface low will track north into Colorado, contributing to a winter storm there. Meanwhile much of the convection will be associated with the cold/occluded front as it pushes east towards the Mississippi Valley. Since the upper level low will be slow-moving (though increasing in forward speed with time), this will allow the storms that form to train over the same areas. Training convection will be of greatest concern as the storms are first forming over Texas. Soils in the area have been drier than normal, meaning most of the rain will be beneficial, however where storms train over more flood-sensitive and urban areas, localized flash flooding remains possible. Wegman Day 3 Valid 12Z Thu Jan 30 2025 - 12Z Fri Jan 31 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MID-SOUTH AND ARKLATEX REGION... ....1930 UTC Update... Again, based on the latest (12Z) deterministic and probabilistic guidance, have nudged the eastern/northeastern peripheries of the Marginal and Slight Risks respectively a bit more downstream. Rainfall amounts have come up across southern IN, southern OH, and eastern KY on Day 3, and although the deep-layer instability will be lacking, 925-850 mb southwesterly inflow and moisture transport anomalies some 3-3.5 standard deviations above normal would support the expansion of the Marginal Risk area. Hurley ....Discussion... Thunderstorms will likely be ongoing on the northern and western sides of the Slight and Marginal Risks at the start of the period Thursday morning. A vigorous upper level cutoff low will begin to rejoin the jet stream by Friday morning. Before it does so however, it will provide the forcing for numerous showers and thunderstorms across much of the Mid-South and Arklatex region. A 50-60 kt LLJ will pump plentiful Gulf moisture across the Arklatex region Thursday morning. The trailing cold front will push east across Oklahoma and Texas, providing ample forcing for the showers and storms. The primary limiting factor for the storms will be instability. The greatest instability (around 500 J/kg) will be across southern and central Texas, while the greatest forcing will be further north from the Arklatex north and east into the Mississippi Valley. This disconnect may help to diminish the flash flooding potential a bit. However, this will be partially offset by upsloping into the Ozarks across Oklahoma and Arkansas. It appears that many of the storms will be associated with a line that moves east across the area. However, storms embedded within the line may move somewhat parallel to the line towards the northeast, this will allow for the potential for training. Since there will be plenty of Gulf moisture (PWATs above 1.5 inches), the showers and storms will have the potential to cause localized flash flooding issues, especially in the terrain of the Ozarks where upsloping may contribute to locally higher rainfall totals. By Thursday night, the storms will push across the Mississippi River. By then the eastward forward speed of the storms should increase, thus diminishing the flooding potential with time. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6MXVJRcTt2c8Lq_ljW6A1vcKTaB5493doNoSVvXaKwB1= bMYwceIG2SuLPFvGoVpxxkUjB7pMQd1DKkiTSyQn7KO3Rik$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6MXVJRcTt2c8Lq_ljW6A1vcKTaB5493doNoSVvXaKwB1= bMYwceIG2SuLPFvGoVpxxkUjB7pMQd1DKkiTSyQndrazjeo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6MXVJRcTt2c8Lq_ljW6A1vcKTaB5493doNoSVvXaKwB1= bMYwceIG2SuLPFvGoVpxxkUjB7pMQd1DKkiTSyQnye_cx8k$=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) .