Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jan 13 2023 04:12:24 AWUS01 KWNH 130412 FFGMPD CAZ000-ORZ000-131315- Mesoscale Precipitation Discussion 0040 NWS Weather Prediction Center College Park MD 1111 PM EST Thu Jan 12 2023 Areas affected...Redwood Coast of Southwest OR and Northwest CA... Concerning...Heavy rainfall Valid 130415Z - 131315Z SUMMARY...Solid meridional Atmospheric River with very slow eastward drift allow for increasing rainfall totals across saturated ground conditions in NW CA and SW OR through much of the morning hours. DISCUSSION...BHX RADAR denoted a weak MCV lifting north parallel to Arcata toward Crescent City along a well defined but narrow nearly due north-south flow ahead of the cold front. This wave was a bit more amplified that much of the guidance suite and therefore with its passing has pressed the trailing confluence axis a bit further east, faster exposing the upper portions of the Lost Coast, Cape Mendocino to the stronger/deeper moisture plume and enhanced rainfall rates. Sfc Tds and deeper layer moisture remains a but further upstream per surface analysis and CIRA LPW Sfc-850mb layer, so this band of rainfall should be more limited in intensity given some sub-cloud drier air and evaporation with rates of .15-.2" expected with some favorable orographic ascent rates of .25-.3" across the western Lost Coast in best orthogonal ascent to the southerly flow (given 55-60kts per BHX VWP). CIRA LPW 850-700 layer suggest best moisture flex remains upstream a bit west of the mouth of San Francisco Bay but will be approaching in timing in the 7-9z time frame coincident with the passage of subtle mid to upper level ridging as a 100+kt 3H jet core slides north and east, exposing the area of concern to better upper level divergence aiding upglide acceleration to the AR plume along and ahead of the slowly approaching cold front. GOES WV suite denotes this well in the broad broken cirrus wedge SW of the NW CA attm. This will further tighten/strengthen moisture flux convergence in the pre-frontal band with core of 1-1.2" Total PWats. This will keep the Lost Coast more exposed to highest rain rates of .5"/hr after 09z. Totals will increase fairly rapidly given expected very slow eastward drift through the early morning hours. Totals of 2-3" should be expected with perhaps best highly focused totals of 4"+ possible by 15z.=20=20 While ground conditions remain highly saturated per NASA SPoRT LIS 0-40cm relative soil moisture values are 80-90% supporting most of the rainfall to runoff further swelling well above normal river and stream levels in the region, the rates are still probably not high enough to induce rapid inundation/flash flooding rates given the Redwood area is a temperate rain forest...and so MPD does not quite rise to FF possible threshold just yet and denoted as Heavy Rainfall/AR tag, especially even into SW OR, where some shadowing may exist due to south to north plume orientation.=20 Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9jg9wbc58J-rGop4cxnvnWO9lMC68D1CVH4dA5KMUDx-n50wm0K1kU1VmGmjD_CJWoKN= GxtlGVtovedRU12Vxa_AtFk$ for graphic product... ATTN...WFO...EKA...MFR...MTR... ATTN...RFC...CNRFC...NWRFC...NWC... LAT...LON 42802434 42672388 42122363 40622344 38922312=20 38682360 39682391 40222440 40742437 41322422=20 42492450=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) .