Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jan 13 2023 08:29:32 FOUS30 KWBC 130829 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 328 AM EST Fri Jan 13 2023 Day 1 Valid 12Z Fri Jan 13 2023 - 12Z Sat Jan 14 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE NORTHERN CALIFORNIA COAST AND ADJACENT MOUNTAINS... The upper trough responsible for the heavy rainfall making its onshore from Washington to northern California early this morning will make its way inland today. Strong vertical ascent has already started over northern California and should become more widespread and greater in magnitude as positive vorticity advection and sufficient 700mb Q-vector convergence aloft approach the coast and then proceeds inland through 18Z. The IVT into California still does not appear to be as strong as what just impacted the Pacific Northwest yesterday, but the NAEFS still shows IVT values >400 kg/m/s south of the Bay Area oriented from the SSW-NNE. With precipitable water values largely in the range between 0.75-1.00" and directed upslope into the coastal ranges by 40-50kt 850-700mb wind (and as far inland as the windward slopes of the Sierra Nevada) periods of heavy rainfall are expected today. Rainfall rates >0.50"/hr are possible in areas where soils remain exceptionally over saturated (NASA SPoRT-LIS 0-40cm soil moisture percentiles >98% for most of the Slight Risk region). Given an uptick in amounts...the northern boundary of the Slight Risk area was pulled north to near Crescent City and extended to just north of the Bay Area. Only minor tweaks were made to the Marginal Risk around the Olympics where another 1-3" of rainfall is forecast and where soils will be more sensitive after Thursday rainfall.=20 Bann Day 2 Valid 12Z Sat Jan 14 2023 - 12Z Sun Jan 15 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR AREAS SPANNING FROM NORTHERN CALIFORNIA TO THE TRANSVERSE RANGE AND THE SAN BERNADINO MOUNTAINS... The next atmospheric river (AR) is already on the way, delivering yet another round of heavy rainfall to California on Saturday and Saturday night. A vigorous shortwave trough will be responsible for ushering in the next slug of anomalous Pacific moisture that contains 0.75-1.0" PWs and IVTs are likely to reach 400-500 kg/m/s given the deep moisture being ushered by west to southwest low on the order of 40 kts which the GEFS shows as being more than 3 standard anomalies above climatology. The heaviest rainfall arrives late Saturday morning and into the afternoon hours as the warm front pushes across the state. A cold front passage later Saturday evening will act to cutoff the best moisture inflow. This AR is more progressive than some of the other ARs that have occurred in recent weeks, which should help to limit the extent of the flooding potential. All that being said, just about all of California; from the coast and both the Shasta and Sierra Nevada on south to the Transverse Range feature soil moisture percentiles >95%. Sufficient moisture and lift associated with this storm still supports a Slight Risk along the North Coast of California, as well as windward, upslope areas below 6,000' along the Sierra Nevada. With an uptick in QPF farther south from WPC and NBM plus support from the finer scale NAM...introduced several targeted Slight Risk areas near the QPF maxima in/immediately near the higher terrain. It remains possible that a targeted Moderate Risk may be needed should rainfall amounts continue to increase or initial environmental conditions worsen, Bann Day 3 Valid 12Z Sun Jan 15 2023 - 12Z Mon Jan 16 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG THE ALONG AND NEAR MUCH OF THE CALIFORNIA COASTLINE... Yet another area of low pressure over the eastern North Pacific ocean heads towards the northern California coast...with one area of moisture arriving along the central coast Sunday afternoon followed by increasing areal coverage by Sunday evening over north in response to the approaching surface low. The best IVT with this wave looks to get shunted more south and east before reaching the coast of North America resulting in lower QPF than with the systems on Days 1 and 2. There is some model agreement in the models about some places north of the Bay area receiving 0.5 to 1.0 inch amounts but less agreement on amounts farther south.=20 Maintained a Marginal Risk area due to the expectation that there will be rain on or near hydrologically sensitive areas. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_uLlNpRX2Y-OkzolVBCbfxnURe4EIXJvVLDVMiP87aap= 8bV21PS05pc7wJ1B8Gtc8xmclXsFh8EobwBXTcwpOPdHlm8$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_uLlNpRX2Y-OkzolVBCbfxnURe4EIXJvVLDVMiP87aap= 8bV21PS05pc7wJ1B8Gtc8xmclXsFh8EobwBXTcwpKjJe9B8$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_uLlNpRX2Y-OkzolVBCbfxnURe4EIXJvVLDVMiP87aap= 8bV21PS05pc7wJ1B8Gtc8xmclXsFh8EobwBXTcwppiIwoU8$=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) .