Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Dec 26 2022 09:03:22 FOUS30 KWBC 260903 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 402 AM EST Mon Dec 26 2022 Day 1 Valid 12Z Mon Dec 26 2022 - 12Z Tue Dec 27 2022 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR COASTAL PORTIONS OF SOUTHERN OREGON AND NORTHERN CALIFORNIA... A shortwave trough will weaken as it drifts into British Columbia today. A potent upper-level low will move into the Pacific Northwest region tonight, kicking off a relatively brief but impactful atmospheric river event. A dying cold front with weak onshore flow will spread rain showers across the coastal ranges of the Pacific Northwest this morning before mostly diminishing this afternoon. A stronger low pressure system will move into the region early this evening, bringing with it a deeper plume of subtropical moisture. PWATs of around 1.25 inches are likely with this moisture regime. Rain rates as high as 0.75in/hr and a 50kt low level jet will contribute to the slight risk of excessive rainfall over the coastal ranges of southern Oregon and northern California. Relatively moist/susceptible soils will provide favorable conditions for flash flooding of burn scars and urban areas. High snow levels will certainly allow for heavy rainfall/flash flooding potential along the windward side of the Cascades. Kebede Day 2 Valid 12Z Tue Dec 27 2022 - 12Z Wed Dec 28 2022 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER COASTAL PORTIONS OF CALIFORNIA AND SOUTHERN OREGON... Anomalous moisture associated with a fast moving atmospheric river will glide down the California coast and Sierra on Tuesday. Moderate to heavy rainfall (rates of 0.1-0.25in/hr) will spread down the state of California where a slight risk of excessive rainfall is in effect. Orographic enhancement and forcing from a cold front will allow for higher amounts over the foothills of the Sierra and heavy snowfall at higher elevations, but a marginal risk will suffice in these areas for now. PWATs near 1.5 inches (4-5 standard deviations from normal) will lead to instances of flash flooding from the Bay area early Tuesday morning to Los Angeles County later in the afternoon. Remnant moisture will spread across the Pacific Northwest, generating heavy snow in the Cascades and modest rainfall over the coastal ranges and Cascades foothills Tuesday morning, where a marginal risk is in effect. Kebede Day 3 Valid 12Z Wed Dec 28 2022 - 12Z Thu Dec 29 2022 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE DESERT SOUTHWEST... The flash flooding threat on Wednesday will remain temporally confined to the morning hours over portions of central and southern Arizona, as remnant moisture from the coastal atmospheric river event pushes through the region along a strong cold front. The latest 00z Euro has come into better agreement with the slower 00z GFS with respect to the arrival of another east Pacific shortwave trough. Thus, heavier rainfall totals are currently forecast to remain off of the northern California/southern Oregon coast on Wednesday. PWATs may hover around an inch with anomalies between 2-3 standard deviations in southern/central Arizona Wednesday morning before quickly shifting southward and diminishing. The marginal risk area is cutoff on the northeastern edge along the Mogollon Rim and White Mountains, where moderate snowfall is expected. Kebede Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_IZ6F29tRofH8lk35cbbQrdOuBFpIH2Zb7vrMgxDYCBv= 8g4VTw-enTK7XgkDo5V0M1ExQVjhnb-Zer-aS_gj0uE_6J0$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_IZ6F29tRofH8lk35cbbQrdOuBFpIH2Zb7vrMgxDYCBv= 8g4VTw-enTK7XgkDo5V0M1ExQVjhnb-Zer-aS_gjsoaNi2A$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_IZ6F29tRofH8lk35cbbQrdOuBFpIH2Zb7vrMgxDYCBv= 8g4VTw-enTK7XgkDo5V0M1ExQVjhnb-Zer-aS_gjp-CDlaM$=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) .