Cooler temperatures this week, with breezy north winds today. First notable precipitation event of the Water Year arrives Wednesday, bringing widespread precipitation, mountain snow, and breezy winds through Saturday. Breezy northerly winds develop again on Sunday.
Discussion
A cool and mostly dry day is on tap for interior NorCal today, as a trough will continue to move east and out of the area. As a result of the trough vacating the area, breezy northerly winds are expected to develop today as pressure gradients will strengthen. The strongest of the northerly winds are expected to develop along and west of the I-5 corridor. The NBM currently advertises around a 30-60% probability of wind gusts of at least 30 mph in the aforementioned areas, with generally 20 mph gusts elsewhere. Relative humidity values of 20-35% and some of the recent light rains should help keep fire weather concerns relatively in check today. High temperatures will in the upper 60s to low 70s across the Valley floor with cooler 40s to 50s in the higher elevations.
Our next weather system will arrive Wednesday as an area of low pressure will continue to dig into the region Wednesday morning. Before the trough moves into the area, periods of breezy southerly winds will develop, with 20-25 mph gusts possible. Later in the day, rain showers will move into the Coastal Range and northern Sacramento Valley with scattered rain showers in the rest of the Valley. More widespread coverage of rain showers and high elevation mountain snow showers will develop later in the evening and overnight hours. Rain showers and mountain showers are forecast to persist until Saturday, although there may be a brief break in the activity in the Valley Friday morning before another wave of showers moves inland.
Recent forecast trends have continued to increase total rainfall and mountain snowfall totals. NBM probabilistic guidance for 0.50″ inches of rainfall across the Valley and Foothills is currently around 40-70% over the three day period (Wednesday-Saturday). Forecast rainfall totals currently range from around 0.25″-2.50″ inches, with the higher totals in the Foothills and in Shasta County.
Chances of snowfall totals of 8″ inches over the northern Sierra are around 40-70% mainly from I-80 southward, with forecast totals now ranging from around 4-12″ inches, with locally higher amounts possible at the peaks. Snow levels are currently forecast to be 5000-6000 feet throughout the duration of the weather system, with a brief period late Friday night early Saturday morning of levels reaching 5000 feet. If you have travel plans through the Sierra later this week, it is strongly encouraged to check quickmap.dot.ca.gov to check road conditions before heading out.
Extended Discussion (Saturday through Tuesday)
EPAC upper ridging builds into NorCal Sunday into early next week resulting in dry weather with warming temperatures. Gusty north to east expected Sunday into early Tuesday.
High temperatures expected to be near to slightly below normal.