October 20, 2019 – Near normal temperatures today then warmer than normal for the remainder of this week. For Monday and Tuesday, light to moderate north to northeast winds combined with decreasing humidities will elevate fire weather concerns. Later in the week, a potentially stronger north to east wind event is possible with even lower humidities and poor overnight recoveries. Models continue to indicate a windy pattern during the period with confidence increasing with regards to timing and impacts. North winds increase during the day on Wednesday over the west side of the valley, then stronger north to northeast winds Wednesday night into Thursday morning for the Coastal Range, northeast foothills and Sierra Nevada. Local gusty northeast to east winds expected to continue Thursday night into early Friday morning in the mountains with light winds expected all other areas.
Discussion
High pressure is currently building over the eastern Pacific and west coast. Most of the north state is under fair skies with some mid clouds skimming over the northeast corner of the state. A small scale disturbance dropping over the ridge might bring a few showers over northern Shasta county today. Otherwise, the forecast area will remain dry today with temperatures remaining a few to several degrees below normal. High pressure continues to amplify over the west coast on Monday bringing a significant warm up on Monday with daytime highs expected to bump up to several degrees above normal. Surface high pressure pushes into the Pacific Northwest on Monday behind todays disturbance. This will bring breezy north winds. This wind combined with the warming and lowering RH will bring elevated fire weather concerns although duration and intensity of the stronger winds will be limited.
High pressure remains over the state on Tuesday bringing more warming and continued dry conditions but overall wind should be a little lighter. High pressure aloft amplifies more over the eastern Pacific on Wednesday bringing more northerly flow aloft over the west coast. This combined with a tight northerly surface gradient will bring increased north winds again especially down the west side of the Sacramento valley and over the coast range. The increased wind and lowering humidity will bring a longer lasting period of elevated fire weather concerns going in to the middle part of the week.
Extended Discussion (Thursday through Sunday)
Main concern in the extended period is the potential for critical fire weather conditions mid to late next week as an upper level trough drops down from western Canada into the Great Basin. As a result, northerly to easterly pressure gradients will tighten, resulting in strong offshore winds. This, in combination with dry conditions and warm temperatures will likely bring critical fire weather conditions. Lighter winds are expected on Friday as pressure gradients relax. Temperature readings will reach into the low and mid 80s in the Valley late next week.
Ensemble guidance indicates another system diving into the region next weekend. This could bring cooler temperatures, as well as another round of gusty northerly winds. Will monitor the potential for additional fire weather concerns during this timeframe.