December 28, 2016 – Dry weather with cool overnight temperatures and patchy morning valley fog this week. Chance of showers by the weekend.
A few high clouds remain over NorCal in the wake of a weather system moving out of the PacNW, but the trend will be toward clearing by sunrise. Temperatures are once again on the chilly side through the Central Valley with current readings mainly in the upper 20s to mid 30s, so frost will be prevalent again this morning. Elsewhere, temperatures range from the upper teens and lower 20s in the colder mountain valleys to the lower 40s in the milder thermal belts of the northern Sierra west slopes and foothills.
Dry weather is expected to continue through the rest of the work week. Overnight temperatures will continue to be below average in the valley the next few nights under clear skies, but we don’t expect hard freeze conditions under building high pressure and a warming airmass.
A cutoff low off the Southern California coast is forecast to push inland on Friday. Models have trended with keeping precipitation associated with this feature to the south of NorCal.
Another closed low is forecast to drop down from the north into NorCal Friday night into Saturday bringing scattered showers. Models continue to show significant differences in the timing and strength of this second system, so forecast confidence is not high.
Extended discussion (Sunday through Wednesday)
Models continue to have differences in track, timing and amount of precipitation for the extended period. Both the ECMWF and GFS show a trough over the Pacific NW digging into NorCal on Sunday into Monday. Best chance for any precipitation will be over the higher elevations during this period.
For Monday night, the models diverge as the GFS pushes the trough eastward and puts NorCal in a dry pattern through midweek. However, the ECMWF keeps the trough lingering over NorCal with continued wet weather into Wednesday.
Confidence in the long term models continues to be poor as they oscillate in their solutions from run to run. Have kept a general chance of rain/snow in the extended until models come into better agreement. As for snow levels and temperatures, these variables are also difficult to nail down details since the GFS starts to show ridging over our region but the ECMWF maintains the trough. If you are making plans for the first week of January, stay tuned to forecast updates since there is the potential for low snow levels and wet weather.