Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Feb 07 2025 00:54:45 FOUS30 KWBC 070054 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 754 PM EST Thu Feb 6 2025 Day 1 Valid 01Z Fri Feb 07 2025 - 12Z Fri Feb 07 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF CALIFORNIA AND THE OHIO VALLEY... ....California... A compact, dynamic system with a vigorous mid level shortwave and=20 strong left exit region upper level jet forcing should support a=20 short duration period of enhanced rainfall rates, although the=20 quick forward motion of the system will limit overall rainfall=20 magnitudes. Given the low-level ageostrophic response ahead of the=20 upper level jet streak, the latest (00Z) GEFS output shows a quick=20 uptick in southwesterly 850-700 mb moisture transport, peaking=20 between 3-4 standard deviations above normal across the central 2/3 of CA Thursday afternoon and evening. Recent model runs continue=20 to show 1-2+ inches falling mostly within 12 hours, with localized=20 amounts of 3+ inches over the coastal ranges and Sierra foothills=20 per the latest high-res guidance. Given the saturated conditions=20 and brief potential for higher rates (0.35+ in/hr) beginning around 21Z along the coast and by 00Z farther inland, this may result in=20 localized runoff issues, especially over burn scars across Santa=20 Barbara, Ventura, and Los Angeles counties. Gallina/Hurley ....TN Valley into the Southern Appalachians... A round of locally heavy rain is in progress across portions of=20 KY, TN, WV and southwest VA near and ahead of an approaching cold=20 front and near the base of a broad shortwave transiting the Great=20 Lakes. While precipitable water values are run of the mill --=20 0.75-1.25" -- the coolness of the atmosphere is leading to=20 significant saturation, which is aiding precipitation efficiency.=20 ML CAPE of 500-1000 J/Kg is being tapped by increasingly surface=20 based convection closer to the front. Thus far, hourly rain totals have maximized in the 0.5-1" range. Given the ingredients above,=20 hourly rain totals to 1.5" and local amounts of 3" remain=20 possible over the next several hours. The decreasing size of the rainfall pattern with time suggests a decline in the risk as we move through the overnight hours. Some of this region (the=20 northeast portion of the Marginal Risk) is more sensitive than=20 normal to additional heavy rainfall given the 2-4" that fell over=20 the past 24 hours. Overall, an isolated to widely scattered flash=20 flood risk appears to exist now that the convective pattern is=20 narrowing and showing increasing progression. The overall excessive rainfall risk is expected to end during the early morning hours of Friday across northern GA, roughly 07z-08z based on the 18z HREF=20 probabilities of 0.5"+ in an hour. Roth Day 2 Valid 12Z Fri Feb 07 2025 - 12Z Sat Feb 08 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Pereira Day 3 Valid 12Z Sat Feb 08 2025 - 12Z Sun Feb 09 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Pereira Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5N0OJCaTCcemOWB2l6MO6NFFGHD58ya-2S0lif4zwfgo= RpAk83uTGBrCCORYno9FV2l31y2XLPvBOdi0DYgW9wtrXIw$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5N0OJCaTCcemOWB2l6MO6NFFGHD58ya-2S0lif4zwfgo= RpAk83uTGBrCCORYno9FV2l31y2XLPvBOdi0DYgWeh_0ol8$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5N0OJCaTCcemOWB2l6MO6NFFGHD58ya-2S0lif4zwfgo= RpAk83uTGBrCCORYno9FV2l31y2XLPvBOdi0DYgWKXHym70$=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) .