Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Nov 19 2024 20:03:20 AWUS01 KWNH 192003 FFGMPD CAZ000-ORZ000-WAZ000-200630- Mesoscale Precipitation Discussion 1159 NWS Weather Prediction Center College Park MD 302 PM EST Tue Nov 19 2024 Areas affected...Coastal Ranges of WA, OR and Northwest CA... Concerning...Heavy rainfall Valid 192000Z - 200630Z SUMMARY...Approach of occluded/cold front into WA/OR after 00z; start of prolonged moderate rainfall with strong Atmospheric River into SW OR/NW CA... DISCUSSION...GOES-W shows a classic evolution of a rapidly deepening 'bomb' cyclone just north of 45N132W, with impressive comma-head baroclinic shield expanding along the NW and N side while a clear slot/descending branch over the SW and southern hemispheres. Central pressures have gone from 1014mb to estimated 955mb from OPC in the last 24hrs. A broad sub-tropical jet cirrus canopy with subtle ridging at the apex of the cold front 42.7N129.5W indicates the anticyclonic rotor of the nose of the 140kt jet directed toward the central OR coast. Clearing aloft, has allowed a view of narrow convective elements along the occluded portion of the front where steep lapse rates/CAA aloft support a narrow ribbon of 500-750 J/kg of SBCAPE. CIRA LPW shows sfc-700mb layers remain very narrow stretched along/ahead of the cold front, before broadening to a broader wedge of slightly above average moisture values south of 38N and west of 134W, approximately delineating a warm front. Enhanced 700-500 moisture hugs the entire length of the mid to upper level jet and portion of the cold front (WSW to ENE orientation) that parallels (generally west of 130W). As such, total PWats of 1-1.25" southwest of the warm front are showing very high moisture flux on 60 to 90kts of 850mb southwesterly flow helping to build IVT values of near 900-1000 kg/m/s. This front will continue to advance quickly toward the coast over the next few hours with similar orientation/northward expansion of the warm front. Further strengthening of the occluded low will bottom out toward mid to upper 940mb range but start a cyclonic loop reducing the surface to boundary layer impetus and expand the occluded front in a northwesterly manner. As such, elevated convection will reduce in forward speed reaching the coast and with further narrowing influences and upper-level jet expanding further eastward into the central OR...convective elements will become more fractured in nature only to increase orographic ascent light rainfall from 1/20th to .1" per hour with scattered streaks of .33-.5"/hr resulting in spotty 1-1.5" totals along favored southwest facing coastal ranges from central OR northward. Further south, the leading edge of heavy rainfall/WAA should be arriving in the 03-06z time frame toward Southwest Oregon and Northwest California. IVT values in the 400-500 range will increase toward 700 kg/m/s by 06z. Weakly unstable air near the triple point and just upstream along the cold front in the warm sector could see enhancement of rates from .5-.75"/hr along or just offshore by 03z. HREF 1"/hr probability reach 50% along the coast by 06-09z, though 1"/3hr values are over 75% with spots offshore near 100% nearing the NW CA coast. At this point, there is not likely to be sufficient coverage/intersection with coastal locations to result in excessive rainfall/flash flooding...though may become more of a risk after 06z. As such, will leave the hazard tag as only Heavy Rainfall expected for this MPD; but this rainfall south of central OR will only set the stage for upcoming likely significant rainfall across the area over the next few days. Please keep attune to further MPDs, AHDs from the National Water Center and flooding/hydrological advisories and statements from local forecast offices over the coming days. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-aoHmH-pg9_tbypJXyH5IpgccCd57z5Fbcvw0YTle1efs_OIdqJmrTmfGQpuSwemuzuD= E2CC-hYKQhjX9vo5iH--CfA$ for graphic product... ATTN...WFO...EKA...MFR...PQR...SEW... ATTN...RFC...CNRFC...NWRFC...NWC... LAT...LON 48362483 47992415 47312359 46222336 44762359=20 43682404 42632396 41762381 41132348 40532340=20 40082363 39962415 40302456 40942483 41312460=20 42102453 42852471 43562456 45212426 46672449=20 47422475 47872490 48102498=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .