Periods of rain with high elevation snow this weekend. Expect scattered thunderstorms at times both Saturday and Sunday. Another wet, warmer system early week bringing moderate to heavy rain, high elevation snow, and renewed flooding concerns.
Discussion
Interior northern California radars are in precipitation mode this early Saturday morning as scattered precipitation impacts the region. Measurable precipitation over the past 3 hours has mostly been confined to mountain and foothills locations along/south of Interstate 80. Radar trends have been slowly increasing over the last hour, and high-resolution guidance suggests that this will continue through the night, likely expanding northward as well.
Unsettled weather will continue into the day on Saturday with scattered to widespread rain and mountain snow showers. 00Z HREF mean CAPE ranges from 100-600 J/kg from around Interstate 80 and points south during the afternoon and evening hours today for Valley and foothill locations. While instability will be decrease after sunset, there will remain some limited CAPE overnight as far north as roughly Chico.
Strong showers and/or any thunderstorms that do develop will have the potential to produce locally heavy rainfall, gusty/erratic winds, small accumulating hail, and even a small chance of funnel clouds (probability is rather low, but undoubtedly non-zero). Convection will likely continue into the day on Sunday with rain showers/thunderstorms as well as mountain snow showers.
Additional precipitation totals through Sunday will vary from location to location as is the case with convective activity. Generally speaking — the Valley can expect another 0.5 to 1.25 inches of rain, and upwards of another 3 to 4 inches in the foothills and mountains below the snow line (roughly 5500 to 6500 ft).
Some of this rain will fall in locations that have maintained a deep snow pack over the last several weeks. This will result in renewed ponding of water issues where the snow pack is slowing and/or preventing the drainage of liquid water.
New snow accumulations of several feet (or more) will be entirely possible above the snow level.
Active pattern will continue on Monday as quasi-zonal flow persists from roughly 40 deg N and points south with troughing across the northern Pacific. Combination is a classic synoptic setup for directing a subtropical moisture tap toward the Golden State (i.e., atmospheric river [AR]). Along the 38 deg N parallel, CW3E AR toolkit shows the 18Z Fri GEFS ensemble Integrated Vapor Transport (IVT) mean peaking around 400 kg/m/s while the 12Z Fri ECMWF EPS mean is higher at roughly 800 kg/m/s for the Tuesday timeframe.
Still some finer details to iron out over the next few days, but we’re undoubtedly still locked into the active pattern through the middle of the week.
Extended Discussion (Wednesday through Saturday)
Lingering showers Wednesday, best chances over the mountains, as upper level trough exits the forecast area. Drier weather returns later Wednesday into Thursday as upper ridging moves through.
Another Pacific storm advertised to push into the CWA Friday, however the system looks weak at this time with limited QPF.
First part of Saturday appears dry under weak short wave ridging, then another weak storm is possible later Saturday or Sunday.