Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Mar 07 2023 08:26:01 FOUS30 KWBC 070825 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 325 AM EST Tue Mar 07 2023 Day 1 Valid 12Z Tue Mar 07 2023 - 12Z Wed Mar 08 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF CENTRAL/EASTERN OKLAHOMA AND NORTHWEST ARKANSAS... The forecast remains on track for the new Day 1 period as the threat of heavy rain increases across portions of the Southern Plains after 00z tonight. An upper-level pattern featuring a longwave trough over the West and a ridge axis spanning from the central Gulf Coast to the Ohio Valley combined with a sharp frontal boundary and increasing moisture will lead to the threat of flash flooding. Shortwave energy rotating through the base of the western trough will amplify the downstream mid-level flow as backing flow aloft over the southern Plains and lower MS Valley will encourage the return of low-level southerly flow. Moisture will become increasingly focused north along a well-defined front draped across the Red River Valley of the South and stretching east-southeast across the lower MS Valley. Initially, the forcing along the front will be rather modest, but by the evening and overnight hours, the arrival of low-amplitude shortwave energy in the deep layer southwest flow aloft along with some uptick in the low-level jet should encourage the development of showers and thunderstorms along and north of the front for areas of central/eastern OK and north-central TX, before gradually shifting into adjacent areas of northwest AR and southwest MO in vicinity of the Ozark Plateau. The initial convection extending to the north of the front is also likely to be co-located along an inverted trough, which will support convergence and stationary/training cells as the low-level jet continues to pump moisture northward. Aside from increasing isentropic ascent, there will also be the nose of at least a modest axis of elevated instability with MUCAPE values of 500+ J/Kg advancing up across south-central OK that will facilitate convective development, with 1000+ J/kg not that far away in northern TX. The PW anomalies increase with time and reach upwards of 3 standard deviations above normal in the 00Z-12Z/Wednesday time frame, with actual PW values close to 1.50" and near the daily max moving average for FWD and OKC according to SPC's sounding climatology page. This will be reflective of not only the low-level Gulf of Mexico moisture transport, but also the infusion of mid and high-level subtropical moisture from the eastern Pacific Ocean which is showing up in a well-defined manner in the global models. The convection that does develop will likely be capable of producing rainfall rates as high as 1 to 1.5 inches/hour given the relatively efficient moisture transport regime and available instability, and the guidance supports the potential for multiple rounds of convection that may repeat/train over the same area. CAMs suggest the potential for maximum rainfall amounts upwards of 3-4" during this timeframe, with the greatest chances for these higher amounts across parts of central and eastern OK. 00z HREF has 30-40% neighborhood probabilities of exceeding 3" here. The only minor trend with recent guidance is to initiate convection farther to the southwest over parts of northern TX and limit the heavy rainfall potential over southwest MO. Additionally, these intense rainfall rates may fall over some relatively sensitive soil conditions as a result of the most recent rainfall event. The latest NASA SPoRT soil moisture anomalies in the 0-40 cm layer are running high (locally in the 80 to 95 percentile range). USGS data also shows streamflows running high along the OK/AR border and over into the Ozark Plateau. Thus, given the sensitive antecedent conditions, and heavier rainfall potential for the latter part of this period, a Slight Risk has been maintained with only minor adjustments to the Marginal Risk area. Scattered areas of flash flooding can be expected within the highlighted area. Snell Day 2 The Day 2 outlook will be updated by 0830Z. 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!99NqF_HGsWRgvrGqHUQuXb4nbGqkNHmib7JEgv5VWY1Y= D9D4BRuVXTo0Dnt9-lozsNaFK2PS38uJ_fquaNS0V6w9_Rs$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!99NqF_HGsWRgvrGqHUQuXb4nbGqkNHmib7JEgv5VWY1Y= D9D4BRuVXTo0Dnt9-lozsNaFK2PS38uJ_fquaNS0fYA2oxk$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!99NqF_HGsWRgvrGqHUQuXb4nbGqkNHmib7JEgv5VWY1Y= D9D4BRuVXTo0Dnt9-lozsNaFK2PS38uJ_fquaNS02_pvSws$=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) .