Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Dec 25 2022 15:54:09 FOUS30 KWBC 251554 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1053 AM EST Sun Dec 25 2022 Day 1 Valid 16Z Sun Dec 25 2022 - 12Z Mon Dec 26 2022 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF COASTAL WASHINGTON AND NORTHERN OREGON... ....16Z Update... No changes were made from the inherited. Light to occasionally moderate rain continues to move into the Oregon and Washington coasts this morning. The rain is likely to become more intermittent and lighter into the afternoon and early evening. However, after that, a strong front with attendant upper level forcing will careen into the coast, causing a rapid increase in rainfall intensity and coverage all over the Pacific Northwest west of the Cascades, with some rain spilling over east of the mountains as well. A south to southwesterly oriented low level jet will favor those facing slopes, which will most dramatically impact the Olympic Mountains and Peninsula where 2-3 inches of rain are expected on already very saturated soils. Further south into the southern Washington and Oregon coastal ranges, 1-2 inches of rain are forecast, so chances of flash flooding should be a bit lower there. Wegman ....Previous Discussion... A pair of surface waves will bring a couple of rounds of moderate rainfall to the coastal ranges of the Pacific Northwest on this Christmas day. The first round of rainfall will arrive with a weak cold front this afternoon. The second round of rainfall will arrive early Monday morning as a stronger cold front supported by an upper-level shortwave trough moves into the region. PWATs will remain modest at around an inch throughout the 24 hour period. Rain rates will remain relatively low as well at around 0.1 in/hr at their peak. The heaviest rainfall footprint is expected to occur over the Olympic mountains where temperatures are expected to remain above freezing. Kebede Day 2 Valid 12Z Mon Dec 26 2022 - 12Z Tue Dec 27 2022 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER COASTAL PORTIONS OF SOUTHERN OREGON AND NORTHERN CALIFORNIA... The slight risk area inherited from day 3 remains mostly unchanged. An atmospheric river event is expected to unfold from the southern Oregon coast to northern California on Monday. Pacific moisture will continue advecting into the Pacific Northwest on Monday morning and afternoon as Sunday's dying cold front pushes into the interior Northwest. PWATs will remain modest, though, around 1 inch. Rain rates will be between ..1-.25in/hr from the coast to the northern Cascades through Monday afternoon. A mid-latitude cyclone supported by a closed upper-level low and a 50-65kt low level jet will kick out the previous system and arrive over the Pacific Northwest early Tuesday morning. A potent moisture regime will follow and overspread the coastal ranges of southern Oregon and northern/central California. Rain rates between 0.25-0.75in/hr are likely early in the morning with the highest rates expected near the Oregon/California border. Moderate to heavy rainfall is likely to make its way into northern portions of the Sierra with this second round of precip, but temperatures should remain warm enough to support rainfall. Flash flooding will be possible over burn scars, urban areas and slot canyons. Kebede Day 3 Valid 12Z Tue Dec 27 2022 - 12Z Wed Dec 28 2022 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE COASTAL RANGES OF SOUTHERN OREGON DOWN TO SOUTHERN/CENTRAL CALIFORNIA... A potent low pressure system will continue to advect anomalous moisture into the West Coast on Tuesday. Pacific moisture associated with an atmospheric river will work its way down the California coast on Tuesday. The upper-level shortwave energy from Monday will open up into a longwave trough as it moves into the Western half of the country. The heaviest rainfall with rates of around 0.1-0.25in/hr will glide down the central California coast Tuesday morning into the afternoon carrying PWATs of around 1-1.5 inches. The greatest flash flooding threat will be over burn scars and urban areas. Freezing temperatures will make their way into the Pacific Northwest and western mountain ranges which will support snowfall in the northern Cascades and Sierra. A 40-50kt low level jet will weaken as the day goes on and the axis of precip shifts southward. Kebede Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4DTh7RIlgo2dd9rfhhRTzUDZFZzPDouwV7nGnixHcADw= 6dNq22KSPZV9nNPYxafLnmP7QK3eV6rt0FEKtK8zlvGhZNU$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4DTh7RIlgo2dd9rfhhRTzUDZFZzPDouwV7nGnixHcADw= 6dNq22KSPZV9nNPYxafLnmP7QK3eV6rt0FEKtK8zS0MYYL8$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4DTh7RIlgo2dd9rfhhRTzUDZFZzPDouwV7nGnixHcADw= 6dNq22KSPZV9nNPYxafLnmP7QK3eV6rt0FEKtK8zPr_lmjc$=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) .