September 19, 2018 – Northerly wind will increase this afternoon into evening becoming gusty overnight into Thursday. Widespread poor humidity recoveries expected tonight with low daytime humidities Thursday. Combination of gusty wind, low humidity, and very dry fuels will result in critical fire weather from this evening through early Thursday evening.
A few high clouds are moving across the far northern portion of the state associated with the passing weak trough. Otherwise, skies are clear across the region. Current temperatures are a tad warmer compared to 24 hours ago across most of the area and range from the 30s in the mountain valleys to the mid 50s to mid 60s across the Central Valley. Upper level ridging strengthens the remainder of the week resulting in warmer temperatures with daytime highs returning to average, or slightly above average.
Locally gusty northerly winds will develop across portions of the Sacramento Valley and surrounding terrain tonight into Thursday with the strongest winds expected Thursday. The warmer temperatures and northerly winds will lower humidity levels over the northern and northwestern portion of our forecast area. This has increased fire weather concerns, and as such a fire weather watch has been issued for this time period. Winds are expected to subside by Friday.
Extended Discussion (Sunday through Wednesday)
The upper trough over the Pacific Northwest will shift east toward the northern Rockies on Sunday, with possibly northerly flow developing across Northern CA Sunday or Monday. Both the GFS and ECMWF are converging on a solution with a Rex Block pattern developing over the eastern Pacific next week, as a closed upper low becomes embedded within a large scale ridge. Confidence is increasing that Northern California will remain under strong subsidence early next week. As such, dry weather is likely to continue through the extended period. We have warmed forecast temperatures several degrees early next week, reflecting the growing confidence in this ridge pattern.