Cold nights, mild afternoons – with a side of smoke

November 13, 2018 – Dry weather with cool nights and above average high temperatures continues through the week. Diminishing winds ease critical fire weather conditions, but widespread smoke from the Camp Fire will continue to impact the area.

Discussion

Plentiful amounts of high clouds are moving across NorCal early this morning in advance of a weakening short-wave off the coast. Current temperatures are a little milder compared to 24 hours ago across most of the region and range from the upper teens to lower 20s in the colder mountain valleys while the Central Valley is seeing readings in the mid 30s to mid 40s (some patchy early morning frost possible again in the outlying areas). Foothill and mountain thermal belts are currently in the mid 40s to lower 50s.

Easterly surface pressure gradient has relaxed somewhat (RNO-SAC is down to around 6.5 mbs), but enough remains combined with the downslope/drainage component for local easterly breezes of 15-25 mph early this morning over ridges and near west-facing canyons of the foothills and west slopes of the northern Sierra.

Persistent upper ridging over Norcal will result in light/lighter winds over NorCal and limited mixing heights (1-2 kft), due to the time of the year, will tend to keep persistent smoke over a large portion of the region for the next couple of days (smoke returned to the northern Sacramento Valley last evening).

With no major changes in the weather pattern through the end of the week, little change from day to day is expected in the forecast. Smoke may help to keep temperatures locally cooler the next couple of days, otherwise they will continue to run above average.

Extended Discussion (Saturday through Tuesday)

High pressure expected to remain over California as we head into the weekend. Temperatures are forecast to remain fairly steady through most of the extended period with the Valley and foothills seeing 60s to low 70s and the mountains in the 40s to 60s. Models continue to hint at a pattern change sometime next week. However, consistency between runs and models is still low. An upper level trough is expected to finally break down the persistent high pressure early next week. There is the possibility that this weather system may bring precipitation to NorCal mid to late next week, but there is low confidence in timing, location, and precipitation amounts between the models at this time.