November 14, 2017 – Mainly dry today then next Pacific storm brings rain and mountain snow, heavy at times, Wednesday into Thursday night. Dry Friday and Saturday, then wet weather returns Sunday into Monday. Winter Storm Watch from Wednesday morning through late Thursday night for West Slope Northern Sierra Nevada-Western Plumas County/Lassen Park.
Weak short wave trough exiting to the east this morning with a few lingering showers possible over the Sierra Nevada. Clearing skies in the Central Valley will allow for some patchy morning fog to develop. Otherwise, dry weather expected today for Interior NorCal with high temperatures near to slightly below normal.
Near vertically stacked system currently in the GOA digs south into EPAC Wednesday and helps to intensify wave presently approaching 30N 140W. Baroclinic zone strengthens as a result, with 1.5+ PW plume taking aim over Interior NorCal tomorrow. Models in better agreement with timing, showing precip spreading west to east across the CWA beginning Wednesday morning.
Strong orographic flow develops over the Sierra Nevada Wednesday night with GFS/NAM-12 showing 60-65 kts of SW wind at 700 MB. This will likely result in heavy snow with strong wind for the mountains of Western Plumas county and the Sierra Nevada.
Periods of heavy snow likely to continue through Thursday afternoon with upwards of 3 feet or more possible at the higher elevations by Thursday night. Snow levels rise during the day Wednesday into Wednesday night to near or above pass levels as WAA increases over the CWA.
Snow levels then lower Thursday as colder air associated with GOA low advects over Interior NorCal. QPF for the Central Valley for Wed/Thu time frames looks to be from around one half to over an inch near the foothills and in the Northern Sacramento Valley. Liquid amounts in the foothills and mountains range from 1 to 6 inches. Models attm showing some post frontal CAPE in the Central Valley Thursday, so may need to consider adding a mention of thunderstorms if trend continues.
Lingering showers possible over the mountains Thursday night into Friday morning otherwise drier Friday as upper ridging builds into Interior NorCal. Some valley fog is possible Friday morning.
Extended discussion (Saturday through Tuesday)
Ridge of high pressure builds across interior NorCal late this week, resulting in dry conditions and near normal highs. After this quiet period, models continue to highlight the potential for an upcoming weather system late this weekend into early next week.
However, its impacts remain uncertain this far out given model differences in terms of timing and evolution. At this point, the GFS is the fastest and wettest model run, favoring a significant moisture surge. Latest forecast models have slowed precipitation arrival, suggesting that precipitation could spread over the coastal range late Saturday evening into early Sunday. Precipitation could then spread southeast across the area on Sunday and linger into early next week (perhaps until Tuesday, if the GFS solution verifies).