Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jan 14 2023 08:26:49 FOUS30 KWBC 140826 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 326 AM EST Sat Jan 14 2023 Day 1 Valid 12Z Sat Jan 14 2023 - 12Z Sun Jan 15 2023 ....THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL FOR AREAS SPANNING FROM NORTHERN CALIFORNIA TO THE TRANSVERSE RANGE AND THE SAN BERNARDINO MOUNTAINS... A progressive upper low off the Oregon coast will direct yet another atmospheric river (AR) at California. Compared the previous ARs in recent weeks the good news is this particular event will be faster moving, meaning California will be subject to a shorter duration of excessive rainfall rates (maxing out between 0.5-0.8"/hr) and somewhat only marginally lower precipitation amounts. At 250mb, a robust 190kt jet streak will place it diffluent left exit region over the southern half of the Golden State by later tonight aiding deep-layer strong vertical ascent in the upper levels of the atmosphere. In terms of moisture, Precipitable water values of 0.75 inches or greater will cover much of California south of the Transverse Range by late this afternoon with values at or slightly greater than an inch along the coast....placing it in the 95th percentile for January and over 3 standard deviations above climatology. Lastly, 850mb winds will be around 35-45 knots on average, which with WSW flow aloft would favor orographic enhancement for rainfall rates, particularly along the central coast of California and the windward slopes of the Sierra Nevada. Meanwhile, farther north and closer to the upper low, 850mb winds of 40-50 knots will be coming out of the west southwest with enhanced 850mb moisture transport aimed at the north coast of California and the southern coast of Oregon. Similar upslope enhancement into the coastal range is expected and has led to global guidance trending wetter in recent runs. Have expanded the Slight Risk there farther north to account for more of southwest Oregon where soils are also sensitive, just not to the extent of their California neighbors. Impacts to California are unlikely to be as significant as some of the predecessor atmospheric rivers over the last couple weeks, but the state remains quite susceptible to heavy rainfall. Portions of the state have picked up 15-20+" of rain and >600% of normal rainfall in the last two weeks. NASA SPoRT-LIS still shows much of the California coast, the Great Valley, the Sierra Nevada, and into southern California with soil moisture percentiles >90%. Most observed rainfall rates are likely to be in the 0.25-0.5"/hr range, but some localized areas could approach 0.8"/hr. Additional flooding is possible along complex terrain, along with the potential for mudslides and ponding on roads. Slight Risks for Excessive Rainfall remain in place from Big Sur on south to the Transverse Ranges, as well as the windward slopes of the Sierra Nevada where snow levels are high enough to warrant periods of heavy rainfall below 6,000'...and saw little reason to make any change to the Marginal Risk placed over the San Joaquin Valley where, while totals are not as heavy as the more elevated areas, still could result in localized flooding. Bann Day 2 The Day 2 outlook will be updated by 0830Z. Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_B_ARwxTcgTtnze2iKctb9nfL9NMxqClUh6Q5t35T134= 86I9e1tV1sfKh3eEku3FMgqieLoAm9956PR36Ftxs88gj60$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_B_ARwxTcgTtnze2iKctb9nfL9NMxqClUh6Q5t35T134= 86I9e1tV1sfKh3eEku3FMgqieLoAm9956PR36Ftxcp6tcbM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_B_ARwxTcgTtnze2iKctb9nfL9NMxqClUh6Q5t35T134= 86I9e1tV1sfKh3eEku3FMgqieLoAm9956PR36FtxhYspQOE$=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) .