Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Dec 01 2022 19:22:32 FOUS30 KWBC 011922 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 221 PM EST Thu Dec 01 2022 Day 1 Valid 16Z Thu Dec 01 2022 - 12Z Fri Dec 02 2022 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS ALONG THE CENTRAL CALIFORNIA COAST... ....16 UTC update... No major changes to the current day 1 marginal risk along the central coast of California proposed. The cold front will continue to steadily progress southward through central California directing an atmospheric river into the coast. Given the transient nature of the AR though, widespread and significant flash flooding is not likely. Still, significant moisture and strengthening onshore flow will support areal averaged total rainfall up to 2 inches in some places with localized flash flooding possible over sensitive locations, with some areas likely to overperform compared to what the guidance would say. A marginal risk still seems appropriate to handle this. See previous discussion below for additional information. Santorelli ....Previous Discussion issued at 0830 UTC... The upper-level trough will move onshore and pass through the Intermountain West while onshore flow with this system overspreads the Coastal Ranges inland to portions of the Sierra Nevadas and southern Cascades. The latest guidance has continued the slight southward trend with the rains that move onshore and the nearly perpendicular flow to the terrain will result in a fair amount of orographically enhanced rainfall. There is a general consensus for localized rainfall rates reaching 0.50 inch/hour (possibly exceeding) along the coastline. The HRRR also is maintaining the lead on some of the highest amounts with rates occasionally exceeding 0.75 inch/hour; but the HRRR and HREF have areal averages near or greater than 2 inches in some of the favored upslope areas. There are several recent burn scars in this part of the state. Rainfall with hourly rates greater than 0.50 inch/hour will increase the threat for rapid runoff which may lead to debris flows in the sensitive burn scar locations and other known vulnerable locations. With colder air filtering into the Pacific Northwest and northern California the snow levels will be falling thus reducing the threat for excessive rainfall. The northern portion of the inherited Marginal Risk area was trimmed down once again due to the southward shift over central and southern coastal California. Campbell Day 2 Valid 12Z Fri Dec 02 2022 - 12Z Sat Dec 03 2022 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF SOUTH-CENTRAL CALIFORNIA... During this period, another fast approaching upper low will drop southward off the Pacific Northwest Coast while a separate plume of moisture remains directed towards the south-central California coast just south of the main upper trough as associated with a trailing cold front. In the Pacific Northwest, the latest guidance continues to trend offshore with the axis of heavier QPF and so the previous marginal risk along the Oregon coast was removed this cycle. To the south, guidance has shifted north with the QPF axis, now directed more towards central California rather than southern, although some uncertainty in placement and amounts continues. Rainfall totals on this day should not be as high as in the day 1 period (as the initial shortwave shifts well inland), although some of the High Res guidance especially continues to suggest some isolated totals near 2 inches in 24 hours, with very localized rainfall rates around 0.5 inch. Despite less favorable heavy rainfall ingredients, a marginal risk was maintained, especially considering heavy rainfall also expected in the day 1 period. Compared to the overnight ERO, the area was pulled northward more consistent with the higher QPF amounts, and as guidance continues to trend much lighter with QPF over southern California. Santorelli Day 3 The Day 3 outlook will be updated by 2030Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6Mt7eYJesabA9KMPJK4cajGm2GWfLdjbskTXtR5_Ibn2= 3BSAqzJD9BSCZ8ly1VDBRdLt5y_lHZUhpU2AOwBw-Uq-bGI$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6Mt7eYJesabA9KMPJK4cajGm2GWfLdjbskTXtR5_Ibn2= 3BSAqzJD9BSCZ8ly1VDBRdLt5y_lHZUhpU2AOwBwmrniAqA$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6Mt7eYJesabA9KMPJK4cajGm2GWfLdjbskTXtR5_Ibn2= 3BSAqzJD9BSCZ8ly1VDBRdLt5y_lHZUhpU2AOwBwzt1GH8E$=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) .