Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jan 09 2023 16:41:21 AWUS01 KWNH 091641 FFGMPD CAZ000-100230- Mesoscale Precipitation Discussion 0033 NWS Weather Prediction Center College Park MD 1140 AM EST Mon Jan 09 2023 Areas affected...Central Valley and Sierra Nevada Foothills of Central California... Concerning...Heavy rainfall...Flash flooding likely Valid 091640Z - 100230Z SUMMARY...Increasing rain rates up to .5" in the Valley and 1" in lower foothills may result in near daily record rainfall that will result in atypical flooding and widely scattered incidents of short-duration rapid inundation/flash flood through this afternoon/evening. DISCUSSION...GOES-W WV suite depicts strong drying surge in the wake of last evening's negative tilt trough passage, while also denoting a broadening cirrus wedge focused onto the central CA.=20 The surface wave is weakening across coastal southwest OR but the associated occluded front is pushing quickly through northern CA attm with fractured scattered convection remaining across the northern Sacramento Valley. However, the warm front has also begun to press through the coastal ranges and the best deep layer moisture of the atmospheric river is allowing for deeper layer of saturated profiles to allow for a deeper column of moderate to heavy rainfall to get across through the southern Sacramento Valley into the northern San Joaquin Valley. Daily record and seasonal 3+ standard Deviation total PWAT values along the coast of 1.25-1.3" per 12z OAK/VBG ROAB will surge across the valley into the lower foothills.=20 Central Valley Floor into Lower Foothills... 12z Hi-Res CAMs suggest the cold front will slowly drop south-southeastward with a strong moisture flux convergence signal along its leading edge, while not driven by instability per se, the increased focus should allow for a narrow band of intense rainfall rates with hourly totals of .5-.75" expected for the central valley due to some short-term training elements. Multiple runs of the HRRR and 12z Conest/ARWs provide some increased confidence for this evolution to manifest particularly after 21z and increasing in intensity further south and east with time as the cold front passes. These hourly rates will near or exceed 12z 1hr FFG values in the area, but given ongoing light to moderate rainfall and overall saturated ground conditions particularly in the lower Foothills where 0-40cm relative soil saturation ratios are over 75% and 2-week precipitation anomalies are well over 300% through much of the region...those static values may be over estimated and so scattered incidents of flash flooding are considered possible. Still, through 03z, rainfall totals of 1.5-2.5" from multiple guidance members near Fresno would actually push all-time top 10 daily totals with 24hr Average Return Intervals in the 50 to 100 year range. So irrespective of short-term localized flash flooding, broad atypical stream/river flooding remains highly probable (please refer to National Water Center AHDs, and local CA/NV River Forecast Center discussions/graphics for further details) across much of the central and eastern Valley out from the Diablo Range rain shadowing area. Lower to Mid-Elevation Sierra Nevada Range... The warm front will quickly surge through the valley by midday and raise freezing levels to 8000Kft to 9000Kft, but the strength of the 850-700mb flow will veer and becoming highly orthogonal to the terrain so even prior to the cold front, the mid mountain will experience 40-65kts of direct flow with 1" of precipitable water allowing for hourly totals of up to 1". Duration as the cold front progresses will allow for totals by 03z to be 2-3" from Plumas to Tuolumne county but increase significantly to above 5" from Madera to Tulare/Kern county line with some strong model consensus of up to 10" locally possible, 6hr FFG values of 3-4" in this area are likely to be exceeded as well, and so spots of flash flooding and atypical flooding on rivers is considered likely.=20 Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4mmz_mSn4XzQF1KosPgaDlos7HTowAZGRDJw5hzxL_6QoNtD4a6RxLjg1QAIbdmYOn4F= zGNlL8GBzIaComhjGT0KDZc$ for graphic product... ATTN...WFO...HNX...STO... ATTN...RFC...CNRFC...NWC... LAT...LON 39852129 39092068 38051987 36831872 35801811=20 35231843 35081920 35441982 36652057 37692130=20 38492149 39282157=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) .