Breezy through Thursday, weekend warming and Fire Weather Watch issued

September 23, 2020 – Chance for a few showers over the northern Coast Range late tonight and early Thursday, otherwise dry weather expected. Temperatures close to average this week, then hot, dry, and potentially windy conditions return over the weekend with possible critical fire weather conditions.

Discussion

Approaching weather system beginning to spread some high clouds across far northern California, otherwise skies are clear across the region early this morning. Onshore flow continues, and surface smoke has mostly cleared from the Central Valley with good to moderate AQI being reported and visibility mostly above 10 miles. Some elevated smoke layers are still being reported across the northern half of the Sacramento Valley.

Onshore flow will persist today and Thursday as the weather system passes to the north through the PacNW. This will keep temperatures gradually trending down a bit, and will bring moderating RH’s. Marine layer expected to return by tonight and we may see some stratus develop across the southern Sacramento Valley early Thursday.

Precipitation from the weather system is forecast to be very slim this far south as the front washes out across the far northern portion of the state. QPF of a few hundredths of an inch will be possible across far western Shasta County early Thursday.

Warmer and drier weather returns for the end of the week as zonal flow retreats north with ridging from the eastern Pacific building into NorCal. Northerly surface gradients forecast to tighten by Saturday resulting in breezy northerly winds in the Sacramento Valley and surrounding terrain leading to a return of critical fire weather conditions. Fire weather watch has been posted.

Extended Discussion (Sunday through Wednesday)

High pressure centered over Northern California on Sunday will remain over the area and becoming more amplified by mid-week. This will keep dry weather in place along with increasing high temperatures through the period. High temperatures each afternoon will be roughly 8 to 15 degrees above average for late September with some locations reaching 100+ degrees on Monday and Tuesday. Widespread moderate heat risk is expected in the Valley and foothills which could impact any sensitive groups including outdoor workers.

On top of the heat and dry conditions, some breezy offshore winds develop this weekend continuing through early next week. This may bring a period of elevated fire weather concerns and a Fire Weather Watch remains in place Saturday through Monday.