Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jan 31 2023 08:12:06 FOUS30 KWBC 310812 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 311 AM EST Tue Jan 31 2023 Day 1 Valid 12Z Tue Jan 31 2023 - 12Z Wed Feb 01 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Chenard Day 2 Valid 12Z Wed Feb 01 2023 - 12Z Thu Feb 02 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF EASTERN TX, NORTHWEST LA, & FAR SOUTHERN AR... Multiple rounds of rain will continue to impact portions of TX into the lower MS Valley over the next 3 days. The risk of some flooding impacts should increase Wednesday into Wednesday night as troughing approaching from the west and an upper jet to the north increases vertical ascent across the region. In the lower levels increasing 850mb moisture transport and convergence should help focus a shower and thunderstorm threat, and with the deep layer mean flow generally parallel to the convergence axis, some repeat activity is probable. Instability is likely to be a limiting factor for this event, with surface temperatures in the 30s and 40s not usually supportive of a notable flash flooding potential. However there will be a strong warm nose above the low level inversion, which will support some weak elevated instability. This combined with the increasing large scale forcing should support some locally heavier convective elements embedded within a broader region of showers...and there is some support for hourly rain locally getting towards 1" in an hour. The magnitude of the flash flood risk remains a bit uncertain given the aforementioned question regarding instability and thus rainfall rates. However a deciding factor for keeping this threat in the Slight risk level is antecedent conditions. Much of the Slight risk areas has seen rainfall the past couple days, with NASA SPoRT-LIS soil moisture percentiles above the climatological 90th percentile and USGS streamflows running above average. Some of this area will see some additional rainfall Tuesday as well, so soil conditions should remain pretty saturated heading into Wednesday. Thus the combination of sensitive soil conditions combined with the uptick in forcing/rainfall rate potential by Wednesday supports the continuation of the Slight risk across portions of east TX into western LA. This area has the best overlap of more saturated soil conditions and potential for rainfall rates getting close to or exceeding 1" in an hour. Locations most prone to flash flooding are atop the aforementioned overly saturated soils, in more heavily urbanized communities that contains a greater concentration of hydrophobic surfaces, and poor drainage areas. Chenard Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_lJyXB2BhpSwoB5FKgnNeiAmBXDi7NpHs5HmZ6xG3lyi= KG-3kdMuQoywceMXZxa73RSCpdx59UXp9MmlzLjkkQHeOFc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_lJyXB2BhpSwoB5FKgnNeiAmBXDi7NpHs5HmZ6xG3lyi= KG-3kdMuQoywceMXZxa73RSCpdx59UXp9MmlzLjkdecTTC0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_lJyXB2BhpSwoB5FKgnNeiAmBXDi7NpHs5HmZ6xG3lyi= KG-3kdMuQoywceMXZxa73RSCpdx59UXp9MmlzLjkZtvyCB8$=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) .