Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jan 23 2023 00:57:26 FOUS30 KWBC 230057 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 756 PM EST Sun Jan 22 2023 Day 1 Valid 01Z Mon Jan 23 2023 - 12Z Mon Jan 23 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Localized swaths of ~1" of rainfall are possible across coastal areas of SC through the evening hours. This area has already seen 1-1.5" of rain with this system, so this additional rain could be enough to cause some isolated minor runoff concerns. However, even with the recent rainfall, 1 hr FFG is still around 2", and given the progressive nature of the convection this evening it is unlikely amounts will get that high. So while some localized low end impacts are possible, the risk of exceeding FFG appears to be below 5%...thus we opted to remove the Marginal risk with this update. Any low end threat that does exist will end in a couple hours anyways as the convection moves offshore. Chenard Day 2 Valid 12Z Mon Jan 23 2023 - 12Z Tue Jan 24 2023 ....1930Z Update... The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 3 Valid 12Z Tue Jan 24 2023 - 12Z Wed Jan 25 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF FAR EAST TEXAS AND THE LOWER MISSISSIPPI VALLEY... ....2030Z Update... The Slight Risk area across far east Texas and the lower Mississippi Valley remains largely the same. A small expansion of the Slight east to include more of eastern/southern MS and eastern LA was included, as the combination of recent rainfall which has thoroughly saturated the soils as evidenced in the NASA SPoRT imagery, and reasonably heavy forecast rainfall in this area should allow for more widely scattered flash flooding. Much larger changes were made to the inherited Marginal Risk. Most notably areas from far northern TX, OK, the northwestern half of AR, and into southern MO are expecting a significant winter storm from this event as the surface low tracks from central TX across southern AR and into the TN Valley. Thus, excessive rain is not expected. Much of central TX has much too dry antecedent conditions, lack of instability, and the rainfall moves off to the east much too rapidly to cause much of an excessive rainfall threat. Similarly across KY, TN, northern MS, northern AL, expect similar lack of instability to be the primary factor resulting in most of the rain being a light stratiform rain, unlikely to produce enough rainfall, much less heavy enough to cause any significant flooding. One small expansion was made to include much of the western FL Panhandle, as storms are expected to develop ahead of the main line, and the area is getting drenched with rain presently. Wegman ....Previous Discussion... The inherited Slight risk area was expanded a bit to incorporate more portions of eastern Texas and the Lower Mississippi Valley. A closed upper level low will lift into the Southern Plains and Mississippi Valley on Tuesday. Meanwhile, the associated southern stream surface low pressures system will strengthen as it glides across the Texas/Louisiana Gulf Coast. Showers and thunderstorms are likely to develop on the leading edge of the attendant warm front lifting up from the Gulf of Mexico beginning Tuesday morning. The general QPF trend has been wetter, due, in part, to a slower evolution of the 500 mb pattern across the southern tier as depicted by the 00z suite of global deterministic models. The ensembles struggle to pin down the timing of the upper trough's progression. The GFS has remained consistent with its diffuse QPF footprint to the north of the other guidance, while the UKMET and CMC are in the best agreement regarding the axis of greatest QPF. Ensemble probabilities of exceeding 2 inches within the slight risk area is currently between 15-35%. PWATs will be between 1.25-1.75in as Gulf moisture surges into the aforementioned areas. Mid-level winds in excess of 50kts and out of the south will help to transport the moist and unstable airmass northward. Rainfall rates are likely to exceed 1in/hr from eastern Texas through Louisiana Tuesday evening. Kebede Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!57WtNr2P8DTKOfe6ku8l2IKU6kfBoigiS6HBB7hQHsQT= PH9-wX9OaKiNpvEA8ld_axSw7TeSy3g_EGngdlsIpey8-tk$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!57WtNr2P8DTKOfe6ku8l2IKU6kfBoigiS6HBB7hQHsQT= PH9-wX9OaKiNpvEA8ld_axSw7TeSy3g_EGngdlsITXR23uI$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!57WtNr2P8DTKOfe6ku8l2IKU6kfBoigiS6HBB7hQHsQT= PH9-wX9OaKiNpvEA8ld_axSw7TeSy3g_EGngdlsIWTz_m1M$=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) .