February 10, 2020 – Breezy northerly winds continue into Tuesday. Dry this week except a threat of showers over mainly the mountains beginning late Thursday and continuing into the weekend.
Discussion
Breezy to windy conditions continue across much of the region early this morning. The north-south surface pressure gradient has relaxed a bit since Sunday, but still remains quite tight with the MFR-SAC gradient currently just shy of 12 mbs (was 15 mbs 24 hours ago). Gusts of 25-35 mph still common in the foothills and along the west side and north end of the Sacramento Valley.
The easterly gradient continues to tighten with the RNO-SAC gradient now slightly above 7 mbs. Gust of 50-60 mph are being observed along the crest of the northerly Sierra, and locally along some of the southwest facing canyons over the west slopes.
The north-south gradient is forecast to continue to slowly subside today while the easterly gradient will remain tight into midday. Breezy conditions will continue in the Sacramento Valley and Coast Range, and winds may pick up again by mid-morning as mixing develops. Windy conditions may linger into the afternoon across the higher elevations of the northern Sierra, and the wind advisory for that area may need extending.
Lighter winds, but still breezy, are expected Tuesday as gradients relax further as the deep closed low to our south begins to shift eastward. Milder daytime temperatures return today and continue into Wednesday.
Next system drops down from the north later Thursday and may bring some showers to mainly the mountains Thursday night. Temperatures may begin to cool a bit across the northern half of the forecast area. Similar to the past few systems, QPF is expected to be very light with little or no impact to travel forecast for the northern Sierra passes.
Extended Discussion (Friday through Monday)
An upper trough originating from the Gulf of Alaska is forecast to move through the PacNW late next week and slide southeast through northern California on Friday. Both the 00z GEFS and Euro ensemble are in fairly good agreement on timing and location of this trough passage. There is a chance of rain and light snow showers as the trough passes, mainly over the Sierra and southern Cascades. The main impact with this system will be another round of northerly winds as the trough axis is expected to deepen east of California over the Great Basin area on Friday. However, at this point winds are looking slightly less impactful as the previous forecast. Will definitely have to keep a close eye on this as the forecast period approaches. This will be a cold system as it originates from the north, so temperatures Friday will cool around 5 to 10 degrees from Thursday to near normal and remain around normal through the weekend.
Upper level ridging returns Saturday, bringing dry weather to interior NorCal. After this, the ensemble models diverge a bit more. Both the GEFS and Euro ensemble depict a weak trough moving along the flow late Saturday/Sunday into early Monday, bringing another chance of precipitation. However, these two models differ on the timing and position and therefore precipitation amounts and location. For now, forecast indicates light precipitation mostly limited to the foothills, mountains, and far northern Sacramento Valley. Increased northerly winds could once again return late Sunday behind the trough passage as the axis deepens to the east.