Dry and milder weather with night and morning Valley fog and stratus expected over Christmas weekend. An extended period of significant wet weather with high snow levels next week.
Discussion
Weak short wave trough moving over the top of West Coast ridge early this morning is bringing a few light showers mainly to the northern mountains. Rainfall amounts have been generally less than 0.10 inches. Some patchy fog will be possible early this morning, but it looks like there will be just enough cloud cover to limit coverage and visibility reduction.
Upper ridge will reamplify this afternoon into Sunday with dry and warmer weather for the holiday weekend. Fog will be possible once again during the overnight and morning hours through Monday. This may limit high temperatures from reaching their peak levels. Current forecast would have high temperatures from the mid 50’s to mid 60’s at Valley locations, but these values could be 10 degrees cooler if fog persists through the day.
Ridge will shift over the Great Basin Region Monday, as broad Pacific trough approaches NorCal with moist southwest flow developing late Monday bringing rain chances to the northern Sacramento Valley during the afternoon and the entire area Monday night.
Extended Discussion (Tuesday through Friday)
We will be in an active weather pattern for the extended period. Long wave troughing will be setting up over the west and this will bring multiple waves of precip. The first round will be with an upper level trough and cold front Tuesday and we will see plenty of moisture ahead of this front with Integrated Water Transport (IVT) pushing to 750+ kg/ms.
A period of moderate to heavy rain can be expected Tuesday. Snow levels will also be high with this system with them above 7500 to 8500 ft, lowering to 5500 to 6500 ft by Wednesday. Activity will become more showery on Wednesday with the best chances over the higher elevations.
Another short wave trough will push west on Thursday and that will bring another round of more widespread precip, though there are some timing differences in the ensembles.
Snow levels with the Thursday system will be lower starting out 4000-5000 feet before rising above 5500 feet during the afternoon.
It looks like we will see another wave of precip next weekend but ensembles diverge even more with timing and exact location for that.
Significant flooding from snow melt is not expected to be an issue at this point since river and reservoir levels are low. However, urban and small stream flooding could be possible on Tuesday, especially in the mountains and foothills. Keep an eye on updates as the forecast unfolds!