November 3, 2020 – Dry weather with above average high temperatures persist through Thursday. Cooler this weekend with a threat of showers, mainly over the foothills and mountains.
Clear skies cover interior NorCal early this morning. Lingering easterly surface pressure gradient is still resulting in some local gusts in the teens mph across the northern Sierra and foothills, but the gradient is weaker and winds are noticeably not as strong as early Monday. RH’s remain very low with local areas still in the single digits and teens percent across the foothills and mountains.
Weakening short-wave will move across the area today bringing an increase in mainly high clouds, but will otherwise have little effect. Temperatures will likely be down a bit. Zonal flow to weak ridging builds back in for Wednesday and Thursday continuing the unseasonably mild daytime temperatures across the region.
Our quiet weather will be replaced by cooler temperatures and shower chances starting Thursday night as a cold upper level trough digs out of the Gulf of Alaska and pushes down the coast into NorCal. A cold front looks to push into NorCal Thursday night, and this will spread showers over the Coastal Range and northern mountains. The cold front sweeps south on Friday with lower snow levels and shower chances continuing over mainly the foothills and mountains. There will be chance for a few inches of snowfall accumulation Friday above about 5k ft across the northern Sierra which will have the potential to result in some travel impacts across the passes. Stay tuned.
Extended discussion (Saturday through Tuesday)
Long wave troughing will be set up over the west coast to start the extended forecast. A short wave trough will dig out of the PacNW into NorCal Sunday morning. This will bring the return of shower chances mainly to the Sierra but can’t rule out the chance for a few showers in the northern San Joaquin around daybreak Sunday. Cold air will be in place and we will see low snow levels 2500-3000 feet. QPF looks very light with this short wave but we could see .5″ to 1″ of snow at pass level and up to a dusting of snow down to around 3000 feet. A few showers will linger over the Sierra mainly south of I-80 Sunday afternoon, otherwise dry conditions set in with clearing skies.
Later Sunday into Sunday night we will see a tightening pressure gradient over NorCal as high pressure builds over the Pacific. This will bring breezy northerly winds to the Sacramento Valley Sunday afternoon and over the Sierra Sunday night. Weak ridging builds in for Monday and Tuesday before another short wave trough tracks towards the region Wednesday.
The cool temperatures will be the other big story in the extended forecast. We will see daytime highs running 5-10 below average and as much as 15-20 below average in the mountains. Overnight lows will also be quite cold as they will fall into the 30s for valley locations and into the teens for the higher elevations.