Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Nov 19 2023 20:05:14 FOUS30 KWBC 192005 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 304 PM EST Sun Nov 19 2023 Day 1 Valid 16Z 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 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). This area of the country has also been very dry the last few weeks, which should help soils retain most rainfall. More specifically, 12z HREF neighborhood probabilities for greater than 2" of rain in 6-hours max out at 20-25% in north-central Oklahoma tonight, but even these amounts shouldn't create a notable flash flood risk. The risk of excessive rainfall and isolated flash flooding is non-zero, but less than 5 percent. Bann/Snell 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... 20z Update... Only minor changes were made to the previous outlook in order to confine the MRGL to an area most likely to see isolated flash flood concerns. New hires guidance, including the 12z HREF, now encompasses the entire D2 period and indicates the potential for localized 2-3" totals. The best chances for these amounts are forecast between northern Louisiana and central Mississippi, where more organized supercells could track and overlap. Here, 12z HREF neighborhood probabilities reach 30-40% for at least 3" in 6-hours. Rainfall amounts up to 2" are possible elsewhere in the MRGL risk and could lead to isolated runoff concerns. In general, the flash flood risk is greatly reduced due to the very dry ground conditions in place. Limiting the flash flood risk to a mostly urban threat. Snell Previous Discussion... 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 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!8wVKprZ95P-yoK31SwMg-ogsME_89BEk8x0Ouk3Dfeqd= DToOpnD-QF1E3fP8mYRJfOJIvUiTqBQ6b_pJMO7UNpX6a2o$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8wVKprZ95P-yoK31SwMg-ogsME_89BEk8x0Ouk3Dfeqd= DToOpnD-QF1E3fP8mYRJfOJIvUiTqBQ6b_pJMO7UjOTL5mU$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8wVKprZ95P-yoK31SwMg-ogsME_89BEk8x0Ouk3Dfeqd= DToOpnD-QF1E3fP8mYRJfOJIvUiTqBQ6b_pJMO7UagM1bWQ$=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) .