Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Nov 11 2025 00:16:23 FOUS30 KWBC 110016 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 716 PM EST Mon Nov 10 2025 Day 1 Valid 01Z Tue Nov 11 2025 - 12Z Tue Nov 11 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Bann Day 2 Valid 12Z Tue Nov 11 2025 - 12Z Wed Nov 12 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Gallina Day 3 Valid 12Z Wed Nov 12 2025 - 12Z Thu Nov 13 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF NORTHERN CALIFORNIA AND FAR SOUTHWEST OREGON... ....20z update... 12z guidance suite shows a quite similar evolution and general timing, if a touch slower, resulting in a slightly northward shift to the overall forecast rainfall placement. As such, a few dozen mile northward expansion of the Marginal Risk across SW Oregon was made, though intersection of the moisture plume/IVT transport is fairly oblique to the SW Oregon coastal ranges, as the deepening triple point lifts northward. Gallina ~~~~Prior Discussion~~~~ A potent cold front and mini-atmospheric river (A.R.) will move into the northern half of California from west to east Wednesday night. This feature will be quite progressive, however the intensity of the A.R. will peak as it moves into California. Guidance suggests 850 mb flow will be southerly into the northern Sacramento Valley at 50-70 kts early Thursday morning. This extremely fast flow will support Integrated Vertical Transport values peaking between 800-1,000 kg/ms. This will support localized rainfall rates to an inch per hour when factoring in upslope effects, especially on south facing slopes and despite a lack of supporting instability. Soils in this area are a bit above normal for this time of year already. The quick hit of heavy rain could very quickly fill local streams and creeks, especially immediately downstream of the mountains, resulting in isolated instances of flash flooding. Snow levels will be between 7,000 and 8,500 ft, which will support only the highest elevations getting snow. Once the cold front driving the heavy rain barrels through around midnight, snow levels will crash to between 3,000 and 5,000 ft. This will be accompanied with much drier air moving in, ending the heavy rain threat. The Marginal Risk area was expanded east with the latest update to include all of the ranges surrounding the northern Sacramento Valley, while maintaining the Marginal threat for the coastal ranges of northern California. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_McIp9glKZEy_3fLEPRpL52klfbJaDG1gE3R9M1GQA0v= Otweqr82NuOgGFmjR_nLFpR0Km1R0H4MYh5OjteOWN0TovA$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_McIp9glKZEy_3fLEPRpL52klfbJaDG1gE3R9M1GQA0v= Otweqr82NuOgGFmjR_nLFpR0Km1R0H4MYh5OjteOwtfo1LQ$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_McIp9glKZEy_3fLEPRpL52klfbJaDG1gE3R9M1GQA0v= Otweqr82NuOgGFmjR_nLFpR0Km1R0H4MYh5OjteONZV1GLI$=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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .