Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jan 27 2023 20:20:26 FOUS30 KWBC 272020 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 319 PM EST Fri Jan 27 2023 Day 1 Valid 16Z Fri Jan 27 2023 - 12Z Sat Jan 28 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Putnam Day 2 Valid 12Z Sat Jan 28 2023 - 12Z Sun Jan 29 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHEAST TEXAS & SOUTHWEST LOUISIANA... ....2030 UTC Update... Only minor modifications were made to the current Marginal Risk area to adjust for the latest 12Z global and hi-res guidance. There remains some concern with the timing in development of storms as the southerly low-level flow ramps up and a coastal warm front pushes northward, with storms potentially not initiating until the end of the day 2 forecast period early Sunday morning. However, several pieces of guidance from both the global and hi-res models agree on the chance for heavy rainfall prior to 12Z, specifically the potential for a few swaths of more intense rain rates in the hi-res guidance. This is supported by a gradual increase in instability near the coast as well as the previously noted influx of anomalously high Gulf moisture. Putnam ....Previous Discussion... A digging longwave positively-tilted trough will direct a weakening shortwave across the Red River Valley and into the Ozarks Saturday night. Meanwhile, deep Gulf moisture will be directed northward from the Bay of Campeche into eastern TX and southwest LA, as a front pushes south and east out of the Plains and into northeast TX through AR. As is typical of most January nights, instability will be the primary limiting factor. MUCAPE across AR will struggle to even get to 100 J/kg. Meanwhile we'll be doing a bit better in that arena further south, especially across southeast TX. Thus, the main change from inherited was to remove the Marginal Risk across much of AR in favor of areas closer to the Gulf Coast. In deference specifically towards the GEM Regional, which is typically a reasonably accurate representation of convective potential around the Gulf Coast, much of the Marginal Risk area was retained across southeast TX and southwest LA. Besides greater instability, the GEM-REG indicates the potential for multiple inches of rain from training convection in the Marginal risk area. Antecedent conditions remain favorable in the Marginal Risk area with nearly saturated soils, though that may be mitigated somewhat by the dry conditions expected between now and Saturday night. PWATs will increase Saturday to 1.5" along the TX Gulf Coast, which is over 2 sigma above normal for this time of year. The LLJ will increase to 50 kt across northern LA/southern AR, while further south in the Marginal Risk area, expect the LLJ to be closer to 30 kt. Nonetheless this will advect plentiful Gulf moisture into the area which will support training convection. While the forcing will be greater further north, again the lack of instability should disallow short-term heavy rainfall rates, even if there are training cells into southern AR. Wegman Day 3 The Day 3 outlook will be updated by 2030Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7A1P__CdErXrxFOF61T4Rjb06gCWGjkZtpPpyAnt1Fs5= l5vy-i2Z5RhcodaK9i_PxmvL6atbAJFHUIUXzBQ-oB-CeRQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7A1P__CdErXrxFOF61T4Rjb06gCWGjkZtpPpyAnt1Fs5= l5vy-i2Z5RhcodaK9i_PxmvL6atbAJFHUIUXzBQ-b3iIopw$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7A1P__CdErXrxFOF61T4Rjb06gCWGjkZtpPpyAnt1Fs5= l5vy-i2Z5RhcodaK9i_PxmvL6atbAJFHUIUXzBQ-ZWr2Fzk$=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) .