Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jan 17 2023 20:22:56 FOUS30 KWBC 172022 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 322 PM EST Tue Jan 17 2023 Day 1 Valid 16Z Tue Jan 17 2023 - 12Z Wed Jan 18 2023 ....16Z Update... The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 2 Valid 12Z Wed Jan 18 2023 - 12Z Thu Jan 19 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE LOWER ARKANSAS, LOWER MISSISSIPPI, LOWER TENNESSEE AND LOWER TO MIDDLE OHIO RIVER VALLEYS... ....2030Z Update... No major changes were made to the inherited Slight Risk area for Wednesday/Wednesday Night. A few minor changes were noted however, based mostly on the latest CAMs guidance... on the southern end of the Slight in LA/AR, most of the guidance suggests very little pre-frontal precipitation before the main squall line moves through. Generally, the further north you go the more prefrontal convection is expected. Thus, other than a nominal westward shift closer to the Texas border per latest trends in the guidance, no changes were made there. The Slight Risk was also expanded a row of counties or 2 north further into southern IL/IN. In these areas, "leftover" convection is being depicted in most of the guidance to remain robust enough to keep the flash flooding threat a concern. The QPF in these areas was increased a bit from inherited as well. The Slight Risk area was also expanded a row of counties or 2 east into western KY and northern TN. Think here the amount of prefrontal rain/storms will be maximized prior to any frontal squall line that may go through there. Either way, training convective cells will be the greatest concern into the evening hours, though lack of instability may limit rainfall rates at any one time. Everywhere in the Slight Risk area, the threat for flash flooding is certainly on the lower side (closer to 15%), both due to lack of instability and overall dry soil conditions. Thus, at this point there is no reason to think any upgrades will be needed. For more on the meteorology, see the previous discussion below. Wegman ....Previous Discussion... PW values expected to rise to 2 to 3 standard deviations above the mean from eastern portions of the Southern Plains, northeastward into the Lower Arkansas, Lower Mississippi, Lower Tennessee and Lower to Middle Ohio River Valleys as low level flow strengthens off the western Gulf in response to strong height falls pushing into the Central to Southern Plains day 2. Strong frontal convergence along the cold front pushing eastward from eastern sections of the Southern Plains toward the Lower Mississippi Valley Wednesday will support enhancing convection in the above mentioned axis of anomalous PW values beginning Thursday morning.=20 There may be a period of training of cells parallel to this front from northern Louisiana, northeastward through eastern Arkansas, western Tennessee and western Kentucky. Hourly rainfall rates of 1"+ possible in area of training. The frontal/pre-frontal convective line should become more progressive Wednesday evening/Wednesday night into early Thursday as it pushes eastward from the Lower Mississippi Valley and into portions of the central Gulf coastal region, lessening the threat of training and heavy rainfall amounts. The slight risk was confined to the regions where training may occur during the first half of the day 2 period and matches the model consensus max qpf axes. The strengthening south southwesterly flow ahead of the strong eastward moving height falls will also support strengthening isentropic lift along and north of the west-to-east-oriented warm front forecast to stretch south of the Ohio River day 2. The slight risk was maintained along and north of this front along and south of the Lower to Middle Ohio River where there may also be a period of training of cells in a southwest to northeasterly direction Wednesday afternoon into Wednesday night. With respect to changes from the previous outlook for this period, no significant changes made to the slight risk area, while the eastern portion of the marginal risk area across Mississippi and Alabama was trimmed westward between 80 and 160 miles. Oravec Day 3 Valid 12Z Thu Jan 19 2023 - 12Z Fri Jan 20 2023 ....2030Z Update... The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!50SG3bDy8_Zcfw-JBuW_p0RT-rUHTv45h21a34rvyhK1= ZYNKLBJOenLPwOhTByeZLxkShAu5Pa9kRMgnezjZ9fJ89ok$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!50SG3bDy8_Zcfw-JBuW_p0RT-rUHTv45h21a34rvyhK1= ZYNKLBJOenLPwOhTByeZLxkShAu5Pa9kRMgnezjZpC6MssE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!50SG3bDy8_Zcfw-JBuW_p0RT-rUHTv45h21a34rvyhK1= ZYNKLBJOenLPwOhTByeZLxkShAu5Pa9kRMgnezjZ7cbTrY8$=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) .