October 8, 2019 – Slightly cooler today, then much cooler Wednesday and Thursday with gusty northerly winds. Temperatures moderate to around average by the end of the week.
Fire Weather Watch from late tonight through Thursday afternoon, Wind Advisory from 6 am Wednesday to noon Thursday. (A Wind Advisory means that constant wind speeds over 25 mph are expected or wind gusts over 40 mph.)
Discussion
Satellite imagery shows the upstream trough dropping down into the PacNW while batches of high clouds spread across NorCal from the west. Current temperatures are a little milder across most of the area compared to 24 hours ago and range from the lower 30s in the mountain valleys to the upper 50s to lower 60s across the Central Valley. Easterly winds are resulting in locally warmer temps in the mid to upper 60s along the eastern edge of the Sacramento Valley into the foothills.
Slight synoptic cooling with the approach of the trough will result in a little cooler temperatures across the region today. The main concern of the week will be the strong winds expected late tonight into Thursday morning bringing critical fire weather conditions to much of the area.
The aforementioned trough will dig into the Central Great Basin on Wednesday, increasing the north and east pressure gradients over NorCal. MFR-SAC gradient is forecast to peak around 14 mbs and RNO-SAC around 12 mbs at 12Z Thursday.
Valley winds will be strongest from the early morning to the evening on Wednesday with gusts in the 40-50 mph range which may bring down some tree limbs and shift any unsecured outdoor belongings.
Overnight on Wednesday, the strongest winds shift mainly to the foothill and mountain regions with gusts 45-55 mph, locally higher for wind prone peaks and areas exposed within northeast to easterly oriented canyons. All locations continue to see these stronger winds through Thursday morning before pressure gradients begin to relax.
Lighter winds and milder temperatures are expected by the end of the week.
Extended Discussion (Saturday through Tuesday)
Light winds return and temperatures remain near or just below average with Valley highs Friday and through the weekend in the upper 70s and low 80s. A weak trough moves across Northern California Saturday night into Sunday. Dry weather continues with precipitation remaining north and west of the area.
The main impact from this weak system will be increased cloud cover over the weekend, mainly on Saturday. Little change is expected early next week. There are hints of some precipitation possibilities mid to late next week, but it is too far out for any confidence at this point.