Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Dec 27 2022 09:06:40 FOUS30 KWBC 270906 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 405 AM EST Tue Dec 27 2022 Day 1 Valid 12Z Tue Dec 27 2022 - 12Z Wed Dec 28 2022 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR COASTAL PORTIONS OF CALIFORNIA, SOUTHERN OREGON AND FOR THE WESTERN FOOTHILLS OF THE SIERRA NEVADA OF CENTRAL CALIFORNIA... Anomalous moisture associated with atmospheric river event spreads southward along cold front today. Upper level troughing moves into the West, sending potent surface wave into Pacific Northwest. The greatest flash flooding concerns remain confined to the western foothills of the Sierra as well as the coastal portions of southern Oregon down through the Bay area and to Los Angeles County where slight risks are in place. Some portions of the coastal Pacific Northwest and northern California that have already received several inches of rainfall over the past 24 hours are especially vulnerable to flash flooding today. The heaviest rainfall (0.1-0.25in/hr rates and +4/+5 Std PWAT anomalies) is likely to occur over the Bay area and Sierra foothills this morning into early afternoon before the moisture plume weakens and sags south. The main excessive rainfall threat should be over by this evening. Kebede Day 2 Valid 12Z Wed Dec 28 2022 - 12Z Thu Dec 29 2022 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF ARIZONA... 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 Southwest along a strong cold front. PWATs may hover around an inch with anomalies between +2 to +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 light to moderate snowfall is expected. Kebede Day 3 Valid 12Z Thu Dec 29 2022 - 12Z Fri Dec 30 2022 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE COASTAL RANGES OF SOUTHERN OREGON, NORTHERN CALIFORNIA AND PORTIONS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY... ....West... Flash flooding concerns return to the West Coast as a pair of low pressure systems arrive on Thursday. The first system will bring a round of rainfall to the coasts of the Pacific Northwest and northern/central California early Thursday morning. Rain rates should be between 0.1-0.25in/hr across the region with PWATs remaining modest at well below an inch. Forcing provided by a weak surface cold front won't help to enhance amounts, but higher totals will still be possible at elevation. The second round of precipitation will arrive with the entrance of another system later Thursday afternoon. Rain rates will be more substantial at around 0.5-1in/hr. PWATs between 0.75-1 inch should cause some flash flooding concerns over already well saturated soils, burn scars and in urban areas. ....Lower Mississippi Valley... An upper trough will move into the Great Plains on Wednesday leading to height falls and the return of southerly flow over the Gulf of Mexico and Mississippi Valley. Moist air advection will ensue with PWATs of between 1-1.5 inches flowing from the central Gulf coast up through the Mississippi Valley and into the Midwest. This moist/unstable airmass, overrunning a coastal warm front, a dry line and cold front to the west, will support convective initiation over the Gulf coast and inland areas, where rain rates may range between 0.25-1in/hr with locally higher amounts. The 00z GFS/UKMET and 06z NAM are in good agreement with the axis of heaviest precip footprint extending into the Midwest while the 00z EC/CMC keep their 24 hour totals confined to the central Gulf coast and ArkLaTex. Thus, the slight risk area is more of a reflection of the latest GFS/UK/NAM suite than that of the EC/CMC. The slight risk area is also consistent with the latest ensemble mean exceedance probabilities of 1 and 2 inches in 24 hours. Kebede Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7A17NifDO1o9ab-1WAypoGiIckpaTUb93YsTGONCX8nN= BJCHjTBaDqCDe6hSv3XllO187itKDGz7rx2Oc-pklmX619Y$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7A17NifDO1o9ab-1WAypoGiIckpaTUb93YsTGONCX8nN= BJCHjTBaDqCDe6hSv3XllO187itKDGz7rx2Oc-pk4gjCXDA$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7A17NifDO1o9ab-1WAypoGiIckpaTUb93YsTGONCX8nN= BJCHjTBaDqCDe6hSv3XllO187itKDGz7rx2Oc-pkOBX_rT8$=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) .