Dry and warmer weather this week. Gusty north to east winds late today and into Tuesday morning will bring periods of critical fire weather to much of the area. Breezy offshore winds may return on Thursday. Red Flag Warning until 11 AM Tuesday for the forecast area and Wind Advisory from 9 AM this morning to 4 PM this afternoon for portions of the Sacramento Valley.
Discussion
Northerly and easterly pressures are rising over OR/NV in the wake of the longwave trof moving through the central US. These pressure gradients bring gusty and drying Nly and Ely downslope winds to our CWA that result in critical fire wx conditions, especially given the seasonal average of the fuels and the prolonged dry conditions. Although there has been an upward spike above average of the 100 hr fuel moisture (due to the most recent trof and wetting rains in some areas) we should see these averages fall rather rapidly to near/below average for today and Tue.
The Ern Pacific ridge axis near/just E of 140W will near the coast today, and will move inland tonite, then into NV on Tue. Anonymously warm air will spread into Norcal mostly at the 700-500 mbs levels that will sustain above normal max temps this week. Adiabatic warming effects from the katabatic wind will push temps into the upper 80s to low 90s in the Valley today or about 8-10 degrees warmer than Sun, along with Min RHs in the 10-12 percent range.
Local gusty winds in the 30-45 mph range overnight are the result of a Nly Barrier Jet that is expected to weaken early this afternoon as the Ern Pac ridge nears the coast. Looks as if this is a marginal wind advisory for the Valley with the strongest winds W of I-5. We anticipate just an hour or two of sustained winds/gusts that could reach advisory criteria in the Valley once the inversion breaks this morning, and until the Nly 925 mbs winds weaken this afternoon.
Although there will be lingering downslope or Ely winds over the Sierra into Tue morning lighter winds and a weak onshore breeze are expected to develop later in the day on Tue as the ridge axis pushes E of our CWA. A dry short wave trof and cold front is forecast to move through Norcal Wed which will increase onshore flow and bring slightly cooler temps to the area. As this trof moves into NV models indicate a closed low will develop and then retrograde over SOCAL forming a Rex Block. While convection is likely over SOCAL, Norcal will be on the dry, anticyclonic side of the pattern with an uptick in max temps for the latter half of the work week.
Extended Discussion (Friday through Monday)
Upper ridge axis along the West Coast Friday with trapped closed low underneath it off the SoCal coast. Low progged quasi-stationary into Saturday then drifts inland across southern portion of CA Sunday, and into the Great Basin Monday. Models depict some associated showers in cyclonic flow but keep precip south of our CWA attm. Main impact for us will be a cooling trend with below normal highs Sunday into Monday.