Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Dec 09 2022 23:48:01 FOUS30 KWBC 092347 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 647 PM EST Fri Dec 09 2022 Day 1 Valid 16Z Fri Dec 09 2022 - 12Z Sat Dec 10 2022 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM FAR SOUTHWEST OREGON INTO NORTHWESTERN CALIFORNIA... Recent water vapor satellite imagery reveals a strong upper level shortwave about 500 miles offshore the OR/CA border moving towards the region. Precipitable water values of 0.75" are pushing inland ahead of this feature per GPS data. Instability is virtually nil, but inflow at 850 hPa is SSW at ~40 kts per the KBHX VAD wind profile. The expectation is for the 850 hPa inflow to increase towards 70 kts and veer slightly, which when combined with the available moisture and low-level frontogenesis slowly edging inland, should yield hourly rain totals of 0.5"+, which has been indicated by the 18z HREF as beginning after 02z across portions of southwest OR, and should shift down the coast of northwest CA with time. The guidance indicates local 3-4" of rain through 12z, which seems reasonable given the rates expected. Freezing levels are quite low, so any heavy rain related issues would be at lower elevation, generally under 5000 feet. The expected heavy rains would be problematic should it impact any area burn scars. Roth Day 2 Valid 12Z Sat Dec 10 2022 - 12Z Sun Dec 11 2022 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ALONG THE COASTAL RANGES OF CENTRAL CALIFORNIA TO THE SAN RAFAEL RANGE... ....Coastal California... Introduced a Slight Risk area basically from the Santa Lucia Range southward to the Transverse Range in Southern California as a deepening upper trough directs an atmospheric river southward along the coast on Day 2. Global models still show strong west southwest low level onshore flow supporting 850-700 mb moisture flux anomalies 3 to 3.5+ standard deviations across the risk areas...and 09/12Z HREF probabilities remain high...60-90%...for 50"+ hourly amounts along the central CA coast for much of the day (with some enhancement in rainfall rates as low-level lapse rates steepen in response to cooling aloft from the afternoon into the evening). The probabilities remain in the 60-90% range as the system builds into parts of southern California during the evening and overnight. Deterministic QPF numbers from WPC increased into the 2 to 4 inch range...which certainly allows for locally higher amounts...and has the potential for flooding where the National Water Model shows above to much above normal stream flow (e.g. around Santa Barbara) and in burn areas. Bann ....Far northeast Texas, southeast Oklahoma into central Arkansas... 2030Z Excessive Rainfall Discussion... Except for a slight southward expansion of the Marginal Risk area in deference to the low-probabilities of 1+ inch per hour south of a front dropping southward...the Marginal Risk area was unchanged from the 0830Z issuance. 0830Z Excessive Rainfall Discussion... A marginal risk area was added across portions of the Southern Plains toward the Lower Mississippi Valley for training potential Saturday along and south of the cold front expected to push east southeastward across this region. Southwesterly low level flow expected to strengthen early day 2 across the Southern Plains, with the potential for training of cells through Saturday afternoon in what will be an axis of PW values 2 to 3 standard deviations above the mean. In area of training, .50-1"+ hourly amounts possible with potential for more than one round of convection to affect a region... In areas of training, isolated runoff issues possible. Oravec Day 3 Valid 12Z Sun Dec 11 2022 - 12Z Mon Dec 12 2022 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTHWESTERN CALIFORNIA... 2030Z Update... No changes were needed to the previously-issued Slight Risk area.=20 Guidance remained consistent in the big picture and the forecast reasoning remained unchanged. Bann 0830Z Excessive Rainfall Outlook Discussion... The axis of anomalous 850-700 mb moisture flux anomalies will continue its southeastward push day 3 into Southern California.=20 Values of 3-3.5+ standard deviations above the mean will push across Southern California during the first half of the day 3 period, supporting heavy rainfall potential from the Peninsular Range westward to the coast and to the south of the eastern portions of the Transverse Range. Overall, there is good model agreement for heavy rains across these areas, with consensus for areal average 1 to 1.5"+ amounts with max totals of 2-3" in the favored terrain regions of the Transverse and Peninsular Ranges.=20 These rains will support localized runoff issues, especially across the numerous burn scar regions of southwestern California. Oravec Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9w87OQTIW8pQRcNuIrhWP8kf_DtcSa7gDMpDRKJ-bPzV= KEUKdCaJjdWxpuGZz_PodRQ7uJUnno2snXegtpXWmWTsnvU$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9w87OQTIW8pQRcNuIrhWP8kf_DtcSa7gDMpDRKJ-bPzV= KEUKdCaJjdWxpuGZz_PodRQ7uJUnno2snXegtpXW-DLGCoM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9w87OQTIW8pQRcNuIrhWP8kf_DtcSa7gDMpDRKJ-bPzV= KEUKdCaJjdWxpuGZz_PodRQ7uJUnno2snXegtpXWZvnN_ok$=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) .