Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Dec 24 2024 13:25:56 AWUS01 KWNH 241325 FFGMPD CAZ000-242200- Mesoscale Precipitation Discussion 1184 NWS Weather Prediction Center College Park MD 825 AM EST Tue Dec 24 2024 Areas affected...Eastern Central Valley & Lower Slopes of Sierra Nevada of California... Concerning...Heavy rainfall Valid 241330Z - 242200Z SUMMARY...Quick hitting AR is starting to weaken, but 1-1.25" of upslope along lower slopes of central and southern Sierra Nevada will continue to pose a heavy rainfall threat into the afternoon. DISCUSSION...GOES-W WV suite shows the very strong cyclone that spurred the strong moisture advection and strong winds with this Atmospheric River has lifted north and is making landfall along/north of Vancouver island into central BC. However, the base of the longer wave trough remains off-shore and is pressing eastward toward the central CA coast. Weak sub-tropical ridging just NE of the right entrance of the polar jet (see upstream wedge of mid to upper level strato-cu with west-east transverse banding signture) well south, generally parallel to Cape Conception.=20=20 CIRA LPW shows a severing of the core of the AR plume about this location as well; combine this with slowly deminishing winds and the AR IVT values are and expected to continue to reduce over the next 6-9 hours, with a continued bifurcation of the moisture plume near surface and mid-levels broadening post-frontally. 13z surface analysis depicts the cold front starting to push though the southern portion of the northern Valley, though low level flow remains backed across the northern Valley. Residual deep moisture and steepening lapse rates will allow for increasing instability and recent HRRR suggests a few lingering convective cores remain possible across the Valley moving southeastward post-frontally and intersecting the already saturated lower slopes of Tehama, Butte and Yuba counties with potential of spotty .5-1" additional totals to maintain ongoing flooding concerns in the area. The main AR core along/ahead of the cold front had an excellent broad, higher reflectivity core that resulted in .5-1"/hr rates but that continues to weaken with the aforementioned reduction of moisture and flux. Still, the leading edge will have solid moisture and fairly orthogonal intersection with the lower slopes of the central and southern Sierra Nevada Range with .75-1" total PWat and 35 reducing to mid-20kt flow to allow for .5"/hr reducing to .25"/hr rates for 1-3 hours resulting in quick .75-1.25" totals. This may near the naturally lower FFG values (.5-.75"/hr or .75-1"/3hr) of within the complex/steeper terrain with a very low but non-zero risk of widely scattered exceedance; though the probability does not rise to FF possible category and will consider this a Heavy Rainfall discussion and likely last MPD for this event as the front rapidly presses through the Sierra Nevada after 21z. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5TIbpStOrameMt-4LqYaC6SYsiivdq3C1ktByVq2Je6Ylbz9ryj49UqPiLWrsfe4tuSL= AmPUffAoGofCkvl6d1KZZgc$ for graphic product... ATTN...WFO...HNX...STO... ATTN...RFC...CNRFC...NWC... LAT...LON 40842182 40332159 39872129 39402079 38882053=20 38312021 37771978 37311927 36931884 35961832=20 35551828 35161864 35101903 35451942 36021972=20 36652015 37312038 37812088 38452114 39162152=20 39702195 40092221 40392241 40692236=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) .