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October 20, 2020 – Dry weather and breezy northerly flow will continue this week with periods of stronger winds resulting in elevated fire weather conditions. Cooler temperatures by the weekend with potentially another strong north to east wind event Sunday into Monday.

Discussion

Pattern remains relatively unchanged as broad ridge extends from the eastern Pacific into NorCal. Skies remain clear other than a few high clouds skirting the far northern portion of the state. North and east surface pressure gradients are once again tightening, and northerly gusts of 15-30 mph are more prevalent early this morning across the foothills and higher terrain surrounding the northern Sacramento Valley. Additionally, current RH’s in the upper teens and 20s percent are common across the same area.

Breezy northerly winds combined with the unseasonably warm temperatures, low RH and dry fuels will result in elevated, locally critical, fire weather conditions today. Very poor RH recovery and continuing breeziness will allow red flag conditions to persist tonight into Wednesday morning.

A series of short-wave troughs moving through the PacNW beginning Wednesday will weaken high pressure over NorCal during the second half of the week. Temperatures will begin to trend down slightly on Wednesday, with a bigger drop forecast on Thursday as highs fall to only slightly above average.

North and east pressure gradients are forecast to tighten again over NorCal on Wednesday night and Thursday as pattern amplifies in response to the deepening trough to our east. Pressure gradients are forecast to be significantly tighter than currently, thus stronger winds are forecast during this time period with sustained north to east winds 15 to 25 mph with gusts up to 40 mph, locally higher over wind prone areas. Breezy winds are likely to continue into Friday. This will renew critical fire weather concerns, and a Fire Weather Watch has been posted.

Extended Discussion (Saturday through Tuesday)

Models have trended with a more eastward track of the weekend short wave trough with it now digging mainly through the Intermountain West. As a result, associated precipitation looks to remain outside of our CWA. Main impact with it now appears to be just some synoptic cooling which lingers into Sunday. High pressure builds inland behind the system Sunday into Monday. This will lead to some increased wind, and possibly elevated fire weather conditions again over portions of interior NorCal. Near normal high temperatures forecast Monday and Tuesday.