Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Nov 19 2023 08:29:33 FOUS30 KWBC 190829 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 328 AM EST Sun Nov 19 2023 Day 1 Valid 12Z Sun Nov 19 2023 - 12Z Mon Nov 20 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. ....Southern Kansas/Northern Oklahoma... Model QPF still suggests that a non-zero threat for excessive rainfall exists across south-central to southeast Kansas and north-central to northeast Oklahoma late as strengthening mid to upper level dynamics are trying to draw favorable moisture/instability ingredients into the region ahead of a sharpening mid-level trough later this evening into the early morning hours on Monday. Precipitable water values only approach 1.3 inches and fairly quick steering flow/cell motion vectors, rain-rates and totals are more likely than not to reach even the naturally lower FFG values of the Flint Hills of SE Kansas into Osage county, OK (<2"/hr). still see the risk of excessive rainfall being non-zero but less than 5 percent. So an incident of flooding can not be fully ruled out, though most rain will be highly beneficial. Bann Day 2 Valid 12Z Mon Nov 20 2023 - 12Z Tue Nov 21 2023 ....There is a Marginal Risk of Excessive Rainfall Over Portions of the Lower Mississippi Valley and Gulf Coast States... Once again...there was very little change to the overall synoptic set-up/evolution on Monday into early Tuesday. The only exception is that the solutions continued to trend faster/more progressive by the latter part of the outlook period and the Marginal Risk area was nudged a bit more to the east. The axis of strongest forcing is still expected to intersect the return moisture flow off the western and central Gulf of Mexico. This flattens the overall flow with increased westerly steering, allowing for a tad increased axis of training/repeating for stronger updrafts along/ahead of the cold front...which when combined with very strong moisture flux...should allow for very intense rainfall rates in the range of 2-2.5"/hr. The big question remains the duration of such rates any place and whether there is repeat convection or training. While the area of concern has been in a longer term drought and top 40cm soil conditions are at or below 30% moisture content (generally below 10th percentile historically), the sheer rates over dry soils may result in limited infiltration initially with increased run-off potential.=20 While an incident or two of flash flooding remains possible, but nearly all parameters continue to fall below thresholds for an upgrade to a Slight Risk. Bann Day 3 Valid 12Z Tue Nov 21 2023 - 12Z Wed Nov 22 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE EASTERN U.S. TO THE GULF COAST... The center of low pressure taking shape on Monday is expected to make its way into the Ohio Valley Tuesday morning and reach the eastern Great Lakes late Tuesday/early Wednesday. A cold front associated with the low will be the primary focus for convection capable of producing heavy to excessive rainfall. There should be plenty of moisture already in place ahead of the front given a period of strong moisture flux. By the latter part of the period...divergence aloft from northern Georgia across parts of the Carolinas and into the Mid-Atlantic region increases as the axis of a 130 to 150 kt upper level jet approaches. This should help supply the upper support while backing low level winds continue to feed low level moisture inland and result in a maximum of low level moisture flux convergence along and east of the front. As was the case on Day 2 farther south...while the area of concern has been in a longer term drought and top 40cm soil conditions are at or below 30% moisture content (generally below 10th percentile historically), the sheer rates over dry soils may result in limited infiltration initially with increased run-off potential. As such, an incident or two of flash flooding remains possible, but nearly all parameters continue to fall below thresholds for an upgrade to a Slight.=20 Closer to the Gulf coast...trimmed the southern portion Marginal Risk a bit but there were still enough signals that locally heavy rainfall could be on-going at the start of the Day 3 period to preclude removing the Marginal risk area all together at this time. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4PwrOrxAy1JAlA_9mFJZ7s6XdM6XJq5MsMLZc_-2bxEj= RZbUKSB1BD5YCvi3lN_07BFvKRVy0ZTcdHSnt_1_-ZHxUYA$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4PwrOrxAy1JAlA_9mFJZ7s6XdM6XJq5MsMLZc_-2bxEj= RZbUKSB1BD5YCvi3lN_07BFvKRVy0ZTcdHSnt_1_YhKRgwg$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4PwrOrxAy1JAlA_9mFJZ7s6XdM6XJq5MsMLZc_-2bxEj= RZbUKSB1BD5YCvi3lN_07BFvKRVy0ZTcdHSnt_1_ukDLUk4$=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) .