Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Apr 09 2023 16:31:46 AWUS01 KWNH 091631 FFGMPD ORZ000-WAZ000-100430- Mesoscale Precipitation Discussion 0173 NWS Weather Prediction Center College Park MD 1230 PM EDT Sun Apr 09 2023 Areas affected...western Washington/Oregon Concerning...Heavy rainfall Valid 091630Z - 100430Z SUMMARY...Areas of heavy rain are forecast to quickly move into the Pacific Northwest coast today in association with an atmospheric river. Rainfall rates may briefly exceed 0.5 in/hr for portions of Washington and 12 hour rainfall totals are expected to range from 2-4 inches from WA to OR through 04Z. DISCUSSION...Recent water vapor imagery showed a potent upper trough off of the west coast of Canada with an embedded shortwave approaching British Columbia. An occluded/cold front was analyzed just ahead of the shortwave, located ~200 miles west of the WA/OR coast at 15Z. Loops of MIMIC-TPW imagery showed a plume of higher precipitable water values rapidly approaching the Pacific Northwest with GPS measurements already at 1.0 to 1.1 inches for the OR coast at 15Z and just under an inch for the WA coast. The forecast moderate strength atmospheric river was located ahead of the Pacific cold front with 850-700 mb winds of 40-50 kt measured at KLGX and KRTX. Rainfall intensity will increase over the next few hours as 850-700 mb winds from the SSW and SW increase into the 50-60 kt range for the WA coast and 40-50 kt range for the OR coast. Precipitable water values will also increase during the event, rising to 1.1 to 1.3 inches, resulting in 600-800 kg/m/s IVT. The increase in low level moisture/warmer temperatures will support increasing snow levels, as high as 8000 ft ASL for the Olympics and Washington Cascades and 10000 ft ASL for western OR. Helping rainfall intensity will be modest diffluence aloft that is expected across coastal WA/OR through the late evening, to the south of an at least 120-130 kt upper level jet (GOES West DMV sampled speeds) located just west of Vancouver Island. The 12Z model components of the 12Z HREF forecast rainfall rates to occasionally exceed 0.5 in/hr for the WA Olympics with the heaviest rain falling between 18-21Z. 0.5+ in/hr rainfall rates are also possible into the WA Cascades and Coastal Ranges while peak rainfall rates for the OR Coastal Ranges largely stay below 0.5 in/hr. Peak 12 hour rainfall totals, ending at 04Z, are expected to range from 3-4 inches for the Olympics and WA Coastal Ranges and Cascades, while 2-3 inches peak rainfall is likely for the OR Coastal Ranges, focused into SSW facing terrain. While the 12Z HREF mean did decrease 24 hour rainfall totals ending 12Z Monday, areas of heavy rain are still forecast with localized impacts possible. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!561oP4DSC0kLbo1jksG1FmYTpdk1Te64lgAu1I49H7zi-T_53QSCrP1hJCI7b5lfrQPs= 6-3xulxBU7jWBoXX5d5KhNE$ for graphic product... ATTN...WFO...MFR...OTX...PDT...PQR...SEW... ATTN...RFC...NWRFC...NWC... LAT...LON 48982178 48862112 47902095 47022129 46142161=20 45582175 45422209 45472231 45722261 45602295=20 45202327 44832346 44172346 43512387 42682410=20 42452432 42472469 42852481 43812451 44852429=20 46292434 47122452 47822479 48092448 48172395=20 48012339 47712298 47122273 46862248 46932215=20 47262192 47572192 47932200 48392214 48672211=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) .