January 10, 2020 – Dry weather today, then a couple of weather systems brush the region over the weekend. A period of light mountain snow is possible Saturday. More significant winter storms may affect the area next week.
Discussion
NorCal in a brief interlude between systems dropping down in NW flow aloft. Satellite imagery shows mostly clear skies across the region early this morning with short-wave ridging moving overhead. IR-difference imagery and surface observations (Cc and Mr) indicating some patchy dense fog across portions of Sacramento County while the remainder of the Central Valley is mostly fog- free at this time. Current temperatures are considerably colder across most of the area compared to 24 hours ago and generally range from the single digits and teens in the mountain valleys to the 30s to around 40 across the Central Valley.
Dry weather expected today, though mid and high clouds will be on the increase ahead of the next system. Precipitation is expected to move inland tonight and spread southward to around the I-80 corridor by 12Z Saturday. QPF is forecast to be similar to the early week system as the main vort slides by further to the north and east. Only a few hundredths of an inch expected in the valley with main quarter to half inch amounts over the mountains (locally higher over the southern Cascade Range).
Another brief break in the weather will be possible Saturday night into Sunday morning, then a couple more systems will be possible Sunday into early next week which may be a little more impactful for winter travel over the mountains.
Extended Discussion (Tuesday through Friday)
The extended forecast remains on track, as you guessed it, long wave troughing dominates the period. Cool and wet weather can be expected during this period as several upper level disturbances track over the region.
The “first” disturbance for the extended period will be exiting the region on Tuesday, with chances for Valley rain and mountain snow gradually decreasing throughout the day. Snow levels with this event are expected to be around 2500-3500 feet and will likely add several additional inches of snow on top Monday’s snow.
Following that, our stronger and wetter storm comes into play mid-late week. Deterministic models continue to deviate from each other, but aren’t as out of sync as they have been the previous few nights. However, confidence is still remains fairly low on exact timing, strength, and location of this system. The NBM guidance has slightly changed, with the most noticeable change being snow levels.
With the latest run, snow still has a decent shot at falling in the lower Sierra foothills, while the northern Valley floor’s seems less likely at this point. Specific storm details will continue to change given this is still far out, so stay tuned to the forecast.