Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Nov 08 2022 09:00:20 AWUS01 KWNH 080900 FFGMPD CAZ000-081700- Mesoscale Precipitation Discussion 1116 NWS Weather Prediction Center College Park MD 359 AM EST Tue Nov 08 2022 Areas affected...Southern California... Concerning...Heavy rainfall...Flash flooding possible Valid 080900Z - 081700Z SUMMARY...Increasing potential for convection with possible training and highly favorable orographic ascent across the Transverse Range into the northern Peninsular Ranges with time. Hourly Rates of .5"+/hr and totals up to 2" pose low-end risk of isolated flash flooding but at least saturate the grounds before next round later today. DISCUSSION...GOES-W 3.9um SWIR loop depicts a weak surface to boundary layer wave near 33N122N lifting northeast toward the Channel Islands. Weak warm advection is resulting in expanding shallow shield precipitation into southern California at this time. This shield is generally a good tracer for enhanced low level moisture and the .85-1" total PWat values. Further northwest the nose of a digging 130kt 3H jet is angling southeastward as the larger scale trof sharpens with weak negative tilting. This will allow for increased diffluence aloft as the jet streak rounds the base of the long wave trof through the morning hours into the early afternoon. This will start with weak divergence aloft, slowly strengthening to become very strong toward 18z when much of S CA is located in the right entrance ascent region of the 130-140kt jet streak. In response, low level flow is going to strengthen in the next 2-3 hours from 15-20kts to 30-35 with weak backing near the surface/boundary layer wave as it enters the Channel Islands.=20 This will increase isentropic ascent and moisture convergence of the 1" total PWats to support shallow convective elements. These elements along with the wave will track favorably into the Transverse Range slowly veering with time and maintaining strong, nearly orthogonal orographic ascent expanding slowly east with time. This will allow for the showers with up to .5"/hr rates to track favorably for isolated 1" totals increasing to 1.5 to maybe 2" through the mid to upper slopes of the mountain range.=20 Given these short intense bursts are through urban areas and fairly complex terrain, isolated flooding concerns could occur but more likely at the bare minimum will set the stage and saturate the upper soils for a second round later in the afternoon and evening with the main cold front. So though this discussion is more for atmospheric river conditions and heavy rainfall cannot completely rule out a possible flash flood particularly in lower vegetation areas in the mountains especially recent burn scar areas.=20 Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_UouS_eft_j0BUV5MXV7qvuuFcfCUROEtsDL_Lrz87hLLjO2C3R3weqkAyjM9OFRDvrr= 6iC3xEX9tcMpEgHDcBCC4Ko$ for graphic product... ATTN...WFO...LOX...SGX... ATTN...RFC...CNRFC...NWC... LAT...LON 34791952 34731882 34641811 34571747 34451706=20 34031663 33481665 33281690 33281757 33621810=20 33671842 33901875 34131946 34251976 34641986=20 =20=20=20=20=20=20=20=20=20=20=20=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) .