Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Nov 25 2022 08:10:09 FOUS30 KWBC 250810 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 309 AM EST Fri Nov 25 2022 Day 1 Valid 12Z Fri Nov 25 2022 - 12Z Sat Nov 26 2022 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE MIDDLE AND UPPER TEXAS GULF COASTS... Another round of heavy rainfall is expected to develop this evening through early Saturday morning across portions of Texas, particularly the middle to upper Texas Gulf coasts, which may lead to some instances of significant flash flooding due to the repeating nature of the storms. As of early this morning, the closed upper low is beginning to move into far western Texas and is expected to slowly track east over the next 24 to 36 hours. After yesterday's rainfall event, there is a lull in activity early this morning with a stationary boundary draped offshore and generally northeasterly flow in place. The bulk of today should be relatively quiet but beginning after 21Z, but especially later tonight into early Saturday morning, another round of heavy rainfall is expected to develop. The combination of the strong upper divergence provided by the closed upper low and a jet streak positioned along the coast will provide favorable forcing for ascent across much of the outlook area. In the low levels, anomalously high moisture is expected to be drawn northward through central and eastern Texas with the latest forecast guidance showing upwards of 1.8" to 2"+ PWs over the risk area by this evening, especially along the Texas coast. With the low level jet ramping up after 00Z and upwards of 30 to 40 kts of inflow at 850 mb, deeper convection should develop and track near the mid to upper Texas coasts through early Saturday morning and the slower progression/movement of the synoptic features likely will allow for training/repeating rounds of convection at times within the plume of deeper moisture. Forecast guidance shows an axis of instability hugging the coast (upwards of 1500 J/kg at times) while lesser amounts of near 500 J/kg spread inland into portions of east-central Texas. The amount of instability and how far inland it reaches remains one of the uncertainties and could impact the intensity of the rainfall and its impacts. At this time, the thinking is that the intense rain (1-2" hourly totals with isolated 3" hourly totals possible) will likely be found along the coast as supported by the 00Z HREF probabilities. Areal averages of 2-3" appear likely with isolated amounts of 3-4" possible within the Moderate Risk area. Over the last 24 hours, portions of this area picked up 1" to locally 3"+ of rain so some of the soils are beginning to saturate with the latest NASA SPoRT soil moisture product shows saturation levels reaching 80-90+ percent for the top 40 cm. As a result, this additional rainfall falling on more susceptible locations (including highly urbanized centers) leads to an increased flash flood risk with some potential for localized/isolated instances of significant flash flooding within the Moderate Risk if the training/repeating rounds set up. Taylor Day 2 Valid 12Z Sat Nov 26 2022 - 12Z Sun Nov 27 2022 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE LOWER MISSISSIPPI RIVER VALLEY AND THE CENTRAL GULF COAST... Locally heavy rainfall will remain possible across portions of eastern Texas, central Gulf Coast, and the Lower Mississippi River Valley Saturday into early Sunday. A closed upper low, slowly moving over Texas, is expected to lift to the northeast during the period, gradually increasing its speed while also weakening and opening up. At the start of the period, a large area of favorable forcing for ascent will be found over eastern Texas immediately downstream of the upper low while in the lower levels, southerly flow will help draw northward deeper moisture. Precipitable water values are forecast to reach or exceed 1.5" in the outlook area, which is between 2-3 standard deviations above normal. However, deeper instability is likely to remain closer to the coast with amounts up to 500 J/kg likely. This should limit the greatest intensity of the rainfall to the coastal areas despite having the deeper moisture lifting well north and the favorable forcing ahead of the progressing upper low. Rainfall amounts of 1-2" over the period are likely in the Marginal Risk area with some signal for isolated higher amounts across southern Louisiana eastward across the central Gulf Coast. Some of these locations picked up a good soaking rainfall in the last 24 hours and as a result, the soils may be a bit more sensitive to additional rainfall. However, the lack of deeper instability and increasing progressiveness of the system offsets a higher risk category at this time and should keep any flash flooding concerns for urban areas or other sensitive flood prone areas. Taylor Day 3 Valid 12Z Sun Nov 27 2022 - 12Z Mon Nov 28 2022 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Taylor Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5w-z8OiFFQeQ3m7wirvEWhJknY6ka29BzJruG6zLWV6r= 1tzv3WmO0uDATMhPp1r1gxivOorHr_8fFIWRWTBBfwwqtpA$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5w-z8OiFFQeQ3m7wirvEWhJknY6ka29BzJruG6zLWV6r= 1tzv3WmO0uDATMhPp1r1gxivOorHr_8fFIWRWTBBnnGTx1M$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5w-z8OiFFQeQ3m7wirvEWhJknY6ka29BzJruG6zLWV6r= 1tzv3WmO0uDATMhPp1r1gxivOorHr_8fFIWRWTBBcJLCVjY$=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) .