Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Mar 04 2023 19:36:56 FOUS30 KWBC 041936 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 236 PM EST Sat Mar 04 2023 Day 1 Valid 16Z Sat Mar 04 2023 - 12Z Sun Mar 05 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. ....16Z update... A shortwave and related cold front was just upstream from northern California at 15Z, with areas of heavy rain impacting locations in the vicnity of Cape Mendocino with peak rates of at least 0.3 in/hr. After the cold front moves inland today, there will be a break in precipitation intensity followed by lowering snow levels down to 1000 feet and potentially down to sea level at times in advance of a second shortwave/precipitation wave which will impact similar areas of northern California tonight. Additional peak precipitation beyond 16Z today through 12Z Sunday is expected to be in the 1-2 inch range below 1500 ft ASL, but some of that will be frozen. Any instances of flooding are expected to be too isolated to warrant a Marginal Risk. Otto ....previous discussion follows... The Marginal Risk for coastal areas of southern Oregon and northern California was removed due to concerns over the realization of any appreciable heavy rainfall. While there could be some totals approaching 1-3", these look to be highly localized and will likely be spread out over a couple rounds of heavier showers with a period of lighter rain in between. Moreover, snow levels will be very low, potentially as low as 1000 feet, removing concerns from additional runoff. Some hail and sleet may even mix in along the coast, lowering the realization of higher rainfall totals from currently forecast QPF in the model guidance. Any impacts from localized heavier totals should be limited to minor ponding. Putnam Day 2 Valid 12Z Sun Mar 05 2023 - 12Z Mon Mar 06 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. The east-central Florida Peninsula is being monitored for locally heavy rain in the vicinity of a west-east oriented frontal boundary. To the immediate north of the frontal boundary will be 10 to 20+ kt of surface to 900 mb flow developing from 18Z Sunday to 06Z Monday over the eastern Peninsula, beneath LFC-EL mean westerly flow of roughly 25-35 kt. 12Z hires models are forecasting 500-1500 J/kg of instability near the front and 1 to 1.5 inches of precipitable water in the pre-convective environment. Added lift/divergence aloft is expected ahead of an upper level shortwave with an associated speed max passing over the region between 00-06Z Monday. If low level winds are stronger than forecast as seen on Saturday morning's guidance, there could be a few cells that develop and are slow moving with rain rates of 1 to 2+ in/hr and localized totals over 3-4 inches. The potential for this scenario is fairly low and thus does not necessitate an outlook on the ERO at this time but the 12Z HREF depicts probabilities of 50+ percent for 3 inches and 30+ percent for 5 inches in the 24 hour period ending 12Z Monday over eastern Florida. Otto Day 3 Valid 12Z Mon Mar 06 2023 - 12Z Tue Mar 07 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Otto Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7QojGGGlE0xPwV9-yCuQ7-1UQAXPlzXeaIYzBFSJi-te= 1gGbc-j7bKn7Jk07wHBH86vjS9pXgYh4PrTmsoAUtt7WXsQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7QojGGGlE0xPwV9-yCuQ7-1UQAXPlzXeaIYzBFSJi-te= 1gGbc-j7bKn7Jk07wHBH86vjS9pXgYh4PrTmsoAUMjEP8eE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7QojGGGlE0xPwV9-yCuQ7-1UQAXPlzXeaIYzBFSJi-te= 1gGbc-j7bKn7Jk07wHBH86vjS9pXgYh4PrTmsoAU6njLmjQ$=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) .