Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jan 27 2025 17:01:36 FOUS30 KWBC 271521 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1021 AM EST Mon Jan 27 2025 Day 1 Valid 16Z Mon Jan 27 2025 - 12Z Tue Jan 28 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. ....16z update... The bulk of stronger convective cells are translating further south and east into the southern deserts of California where the risk of flooding is reduced. Still, as the upper-low spins directly over=20 Southern California, some lingering lingering showers may still=20 intersect with the most at risk burn scar areas over the next=20 3-6hrs. Still, the potential for .25"/hr rates is well below=20 earlier this morning and about 10-15% . Given these probabilities=20 there remains a few more hours of non-zero risk; but the coverage=20 potential falls below the 5% for a categorized area, and so the=20 Risk area was removed with this update. Gallina ~~~~Prior Discussion~~~~ Light to moderate shower activity in association=20 with a deep closed low looks to continue for a bit longer early=20 this morning over portions of Southern California, gradually=20 diminishing by midday as the low weakens and pivots inland and=20 brings an end to the (now very low) potential for sub-hourly=20 (15-min) rainfall rates of 0.25"+. Maintained the inherited=20 Marginal risk for excessive rainfall for this very low-end=20 potential, primarily due to elevated concerns for any lingering=20 shower activity over the recent burn scars. This activity should=20 largely come to an end by 18z, and the Marginal risk will likely be discontinued with an update later this morning or afternoon. Churchill Day 2 Valid 12Z Tue Jan 28 2025 - 12Z Wed Jan 29 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Churchill/Wegman Day 3 Valid 12Z Wed Jan 29 2025 - 12Z Thu Jan 30 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF NORTH TEXAS AND SOUTHERN OKLAHOMA... An upper level cutoff low ejecting out of the Southwest into the Plains will provide the forcing for ascent for a developing low over North Texas Wednesday and Wednesday night. Return flow of Gulf moisture ahead of the low will advect north into Texas and Oklahoma along with increasing instability. The typical diurnal increase of the LLJ Wednesday night will greatly increase the coverage and intensity of storms along the developing low's cold front, while the warm front locally increases lift into Oklahoma. Since the upper level low will be slow-moving (though increasing in forward speed with time), this will allow the storms that form to train over the same areas. Soils in the area have been drier than normal, meaning most of the rain will be beneficial, however where storms train over more flood-sensitive areas and urban areas, localized flash flooding is possible. Ensemble guidance have increased in the areal coverage of at least 1 inch of rain, though the pattern is much more favorable to narrow streaks of much heavier totals where the storms track. Thus, confidence has increased enough to introduce a Marginal Risk area. The more significant flash flooding risk will be largely north and east of the Day 3 Marginal Risk area going into D4/Thursday. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!61CwTyyYqutgZQDg5H5J9HcaLALt5-kqZBuVvrLhlLxc= fqyzcRC_BoWMZxdPmlTcODOtoZCJb2U97r0M9sb3A0Orz-U$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!61CwTyyYqutgZQDg5H5J9HcaLALt5-kqZBuVvrLhlLxc= fqyzcRC_BoWMZxdPmlTcODOtoZCJb2U97r0M9sb3G2415H0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!61CwTyyYqutgZQDg5H5J9HcaLALt5-kqZBuVvrLhlLxc= fqyzcRC_BoWMZxdPmlTcODOtoZCJb2U97r0M9sb3ctAnO8o$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .