February 12, 2020 – Dry this week except a chance of showers over mainly the mountains this weekend. Above average temperatures continue.
Discussion
Some high clouds are beginning to spill into NorCal as the eastern Pacific ridge weakens. Surface pressure gradients are much weaker for the most part compared to 24 hours ago, but enough of a northerly gradient remains for local gusts in the 15-25 mph range across portions of NorCal.
Current temperatures are considerably cooler compared to 24 hours ago where winds were still gusty yesterday. Readings range from the 20s in the mountain valleys to mainly the 40s across the Central Valley (Red Bluff still 55 with a northerly wind around 10 mph).
Temperatures will cool a bit the next few days as high pressure weakens, but will still remain above average with dry weather continuing. The next system is forecast to drop from the north late Thursday into Friday. Latest deterministic and ensemble guidance has trended drier with this feature as the best dynamics will remain north of the area. Better chance of showers over mainly the mountains beginning late Saturday, but QPF is forecast to be very light.
Extended Discussion (Sunday through Wednesday)
A progressive shortwave will swing north of the region on Sunday allowing for some residual showers, particularly across the foothills and higher terrain. Depending on how much moisture is left, perhaps snow accumulations up to an inch may fall around 5,000 feet and above. As this system exits the region, tightening pressure/height gradients will support a period of enhanced dry, northerly flow which may continue until Tuesday. This will maintain another period of low daytime relative humidities.
As the trough continues to edge eastward, an upstream ridge begins to take shape over the West Coast. The guidance eventually tries to close off an upper low over the southwestern U.S. by the middle of next week. The main implications of this pattern would be increasing easterly, downslope flow. However, there is a tremendous amount of ensemble uncertainty so will remain something to keep an eye on. Overall temperatures throughout next week will remain a degree or two above climatology.