Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jan 13 2024 09:21:19 AWUS01 KWNH 130921 FFGMPD CAZ000-ORZ000-132120- Mesoscale Precipitation Discussion 0014 NWS Weather Prediction Center College Park MD 420 AM EST Sat Jan 13 2024 Areas affected...Far Southwest OR...Northwest CA Concerning...Heavy rainfall...Flash flooding possible Valid 130920Z - 132120Z SUMMARY...Heavy rains to overspread the coastal ranges of far southwest OR and northwest CA going through the day on Saturday as a quick-hitting and relatively modest atmospheric river moves ashore. Some flooding concerns may materialize at least locally given the expectation of locally several inches of rain. DISCUSSION...The latest GOES-West satellite imagery shows a shortwave trough amplifying gradually down to the southeast in the vicinity of 44N and 140W along with a surface low and attendant frontal zone. This energy over the eastern Pacific Ocean is seen tapping into a pool of subtropical moisture that is advancing northeast up around a deep layer cyclone/gale center near 27.5N and 150.5W to the northeast of Hawaii. The latest NESDIS Blended TPW and CIRA-ALPW products show an axis of higher PWs/deeper moisture focused near this low and northeast up along the cold front that is connected into the low center offshore of the Pacific Northwest. Over the next several hours, this low center will be losing latitude and gradually approaching areas of far southwest OR and northwest CA which will begin to strengthen the warm air advection and moisture transport into the coastal ranges. The latest GOES-West IR satellite imagery shows cooling cloud tops offshore of western OR and suggestive of stronger forcing/divergent flow aloft associated with the digging shortwave and related DPVA parameters. This will begin to overspread the coastal ranges early this morning and continue through the midday time frame while coinciding with strengthening Pacific moisture flux. The result will be the arrival of moderate to heavy rain with rates increasing with time. The low-level jet ahead of the low center is forecast by the latest hires model consensus to increase to as much as 50 kts by 18Z today with IVT magnitudes increasing to as much as 500 to 750+ kg/m/s. The overall deep layer moisture axis/atmospheric river should become aligned generally orthogonal to the terrain between 15Z and 21Z today which will favor greater orographic ascent and heavier rainfall rates for the coastal ranges. A cold front will then arrive after 21Z and advance inland. Generally the 00Z HREF models support rainfall rates increasing to around a 0.50"/hour by 15Z across Curry County in far southwest OR, and into Del Norte and Humboldt County of northwest CA. The rainfall rates are forecast to peak locally as high as 0.75" to 1"/hour in the 18Z to 21Z time frame as the peak IVT values arrive just ahead of the cold front. Some convective elements associated with instability pooling up along the cold front will help facilitate these heavier rainfall rates. 12-hour rainfall totals going through 21Z today are forecast to be as much as 3 to 6 inches, with the heaviest amounts over the northwest CA coastal ranges. This is consistent with the 00Z HREF consensus. Given the higher rainfall rate potential for at least a few hours today, and the overall storm totals, some areas of flooding will be possible and this may include not only the more sensitive urban areas, but also a couple of the burn scar locations which will need to be closely monitored. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!90og3d2lbzRA1HEdui6dVGMpv9NRlr_BCSDXt_6ex30HBZ0pDMkDzPDpsolXj7rpaqXZ= ML_d29fB8qMNjtz2ut5eiOQ$ for graphic product... ATTN...WFO...EKA...MFR...STO... ATTN...RFC...CNRFC...NWRFC...NWC... LAT...LON 42852419 42602373 42042348 40902341 40352339=20 39842324 39342305 39052327 39052383 39592408=20 40192456 41442440 42472463=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) .