Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jan 18 2024 23:24:11 FOUS30 KWBC 182324 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 622 PM EST Thu Jan 18 2024 Day 1 Valid 01Z Fri Jan 19 2024 - 12Z Fri Jan 19 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF WESTERN WASHINGTON... A Marginal Risk was maintained across portions of western WA, where moderate to heavy rainfall, along with snow melt in some areas caused by rising freezing levels, may lead to excessive runoff. Guidance shows precipitation spreading north, with frontogenesis near 850 hPa stuck across western WA helping to enhance convergence. GFS and ECMWF IVT indicate significant moisture transport into the region. Inflow at 850 hPa out of the south reaches 40 kts, but instability should be meager at best.=20 Local amounts of 3-4" are possible across the region, which is problematic for the Skokomish River. The heaviest amounts are expected along the southern slopes of the Olympics, where upslope flow is likely to bolster amounts. Hourly rain totals peaking near 0.5" during the 05-12z period when combined snow melt raises the threat for isolated excessive runoff. Roth/Kebede/Pereira Day 2 Valid 12Z Fri Jan 19 2024 - 12Z Sat Jan 20 2024 ....THE PROBABILITY OF RAINFALL EXCEEDING FLASH FLOOD GUIDANCE IS LESS THAN 5 PERCENT... Guidance has trended lighter over north-central California on day 2 (12z Friday - 12z Saturday), so we decided to remove the inherited Marginal Risk area that encompassed parts of Sonoma, Mendocino, Lake and Napa Counties. Guidance is still in agreement on a QPF bullseye over parts of northern Sonoma County for the 24 hour period ending 12z Saturday. Timing-wise, rainfall should begin around Friday afternoon and pick up in intensity around 02-03z. 12z HREF doesn't have rates ascending beyond 0.1"/hr which shouldn't cause any Flash Flood Risk for that area, especially since they're not very saturated. Kebede Day 3 Valid 12Z Sat Jan 20 2024 - 12Z Sun Jan 21 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF NORTHERN CALIFORNIA AND SOUTHWEST OREGON... ....2030z Update... The details mentioned in our previous discussion remain mostly the same for the period ending 12z Sunday. The northern periphery of the Marginal Risk are was extended north to include parts of Coos, Josephine and Siskiyou Counties, in collaboration with the local forecast office. The NBM as well as our QPF has increased by 1-2 inches over many places within the Marginal Risk area. Widespread 2-3 inches are expected with some higher amounts possible in the 24 hour period. Kebede ....Previous Discussion... Precipitation will continue to spread across the region as a mid-to-upper level shortwave slowly drifts onshore. While guidance shows the leading IVT plume continuing to weaken as it moves further inland, westerly to southwesterly flow south of the parent low is forecast to tap some deeper moisture, directing it inland across the region as it weakens and nears the coast on Saturday. The 00Z deterministic and ensemble guidance was overall in generally good agreement indicating that 1-2 inches, with locally heavier amounts likely within the highlighted region.=20 This along with the wet antecedent conditions may raise isolated runoff concerns. Pereira Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4JDeUUSSVKnfhBvP4GkgXHKT8acxOp-iYvW1kNdGUgXR= 064DddAL9ZCvE2ckE2BZ6WGC-hz2An_-Gn-L9XKzq7KgEXY$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4JDeUUSSVKnfhBvP4GkgXHKT8acxOp-iYvW1kNdGUgXR= 064DddAL9ZCvE2ckE2BZ6WGC-hz2An_-Gn-L9XKzTEpiZLI$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4JDeUUSSVKnfhBvP4GkgXHKT8acxOp-iYvW1kNdGUgXR= 064DddAL9ZCvE2ckE2BZ6WGC-hz2An_-Gn-L9XKzrK2PtlI$=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) .