Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Nov 20 2024 20:30:32 AWUS01 KWNH 202030 FFGMPD CAZ000-210600- Mesoscale Precipitation Discussion 1161 NWS Weather Prediction Center College Park MD 329 PM EST Wed Nov 20 2024 Areas affected...Northern California... Concerning...Heavy rainfall Valid 202030Z - 210600Z SUMMARY...Strong, persistent heavy rainfall signal continues into north-central coastal Range and starting to bleed over to the northern Sierra Nevada range with times of .5-.75"/hr rates and additional 3-4" totals by 06z.=20 DISCUSSION...GOES-W WV suite depicts a weak baroclinc leaf with transverse banding lifting northeast toward and starting to intersect with the SW Oregon coast, this is indicative of a broadening right entrance to the polar jet and short-wave ridging across northern California. As such, the forward progression of the front has fully stalled with weak rain-cooled support pressing the pre-frontal convergence/isentropic band across Sonoma/Santa Rosa counties at this time. The upstream edge of the divergence pattern aloft well-offshore is helping to spur a weak surface low along the front which will help lift the best moisture flux convergence axis northward after 23-00z with some increased southerly flow at the coastline, shifting the axis back to Menodcino county later in the valid time period (03-06z).=20 Recent surface observations have seen dew-points rising through the San Francisco Bay and filtering into the Sacramento Valley, suggesting the warm front has over-topped or is near over-topping the coastal range. CIRA LPW hints at this as well with .5-.75" at the sfc/850mb layer pressing through the north-central CA coast.=20 LPW also denotes better alignment through depth and so moisture totals are reaching 1.3" and nearing 1.5" just upstream off-shore. Total IVT ranges are about 750-900 kg/m/s along and just offshore, given said moisture and continued solid 50-60kts of fairly orthogonal 850mb flow in the core of the PW plume. As such, ..5"/hr rates in the coastal range are increasingly probable supported by 50-75% neighborhood probability along the coastal range wavering north/south with the passing surface inflection toward 03z. Totals across the coastal range vary from 2-4.5" and soils are starting to fully saturate. FFG values along the spine are about 1.5"/3hrs and given the recent saturation, it is becoming increasingly plausible of exceedance but probably probability still remain just below threshold.=20 As mentioned, deeper moisture is filtering through the Sacramento Valley, though cooler and drier air remains coincident with the front range, this further intensifies the isentropic ascent plane increasing verticality of of the showers. Core of the plume still appears directed at the Butte/W Plumas county slopes, and HREF probability of 1"/hr reach 15-20% suggesting a spot or two for a few hours are likely to reach .75"/hr of rainfall, peaking in the 23-01z time frame. Even IVT values are in the 600+ kg/m/s range supporting this potential.Persistence of southwesterly warm-air advection will press freezing levels steadily up slope as well, broadening the area of moderate to heavy rainfall in steeper terrain. Similar but slightly higher 1.5-2"/3hr FFG values exist across this area and while there is increased potential for higher intensity rates, the duration of moderate to heavy rainfall pre-cursory to this surge has been limited relative to the coast.=20 While a spot or two of FFG exceedance is possible, it will need to be monitored closely...but will continue to maintain a Heavy Rainfall tag for this MPD valid time. Further north toward Cape Mendocino into the SW slopes of the Trinity Range... The core of the moisture will continue to be focused south, but given proximity to the stationary front/triple point, convergence should be maximized to allow for similar occasional upticks to ..5"/hr. Given this area has the climatologically wetter climate and higher natural FFG values, the risk for flooding will continue to be better accommodated than further south. Though and additional 2-3" rainfall expected; this further saturation will result in greater run-off further setting the stage for expected activity over the next coming few days. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9xDAmHd0dfUfszK6USAAuGP2uXiKZFEHFeccEVhVueDyl15euGpcO2pRhLV0bGHSAjo9= jRsvBSK4K2yv0Y6fPc8nx7I$ for graphic product... ATTN...WFO...EKA...MTR...STO... ATTN...RFC...CNRFC...NWC... LAT...LON 41782411 41612388 41312362 40982347 40982270=20 41072204 40152159 39422087 38702061 38422091=20 38292172 38102232 37872287 38332328 38832377=20 39622397 40022422 40352452 40642443 41242428=20 41672428=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) .