October 6, 2017 at 10:29 AM Update: The National Weather Service in Sacramento has issued a Red Flag Warning, which is in effect from 11 PM Sunday to 5 AM PDT Tuesday. The Fire Weather Watch is no longer in effect.
October 6, 2017 – A little warmer than normal today and Saturday. Dry and a little cooler with moderate to strong north winds early next week for increased fire danger. Lighter winds and cooler temperatures for the second half of next week. Fire Weather Watch from Sunday evening through late Monday night
Discussion
High pressure aloft over the west coast bringing fair skies and a little warmer temperatures this morning. Significant airmass warming aided by light northerly surface winds will bring a significant warm up today with highs climbing to between 5 and 10 degrees above normal. A weak frontal system moving through the Pacific northwest on Saturday will bring a slight cooling effect to the forecast area mainly over areas from Sacramento northward. This system and its associated upper trough will dig into the great basin on Sunday allowing surface high pressure to build behind it over the Pacific Northwest.
By mid day Sunday, MFR to SAC surface gradient is forecast to top 10 mb with northwest upper level flow bringing moderate upper level support for breezy northerly winds. Cooler air pushing into the area will bring down daytime highs down to near normal but northerly winds will usher in drier air for decreasing humidity.
Combination of winds and low RH will bring increased fire danger starting Sunday and a Fire Weather Watch remains in place Sunday afternoon through Monday. Northerly surface gradient becomes quite strong maxing out Sunday night with GFS and ECMWF models showing a 15 mb MFR to SAC surface gradient.
Could see wind gusts along the the west side of the Sacramento valley topping 40 mph if current models verify. Surface gradients and winds decrease slowly during the day on Monday but remain breezy through the day and overall airmass continues to dry. The northern Sacramento valley could see minimum RH values drop into the single digits. Temperatures warm slightly on Monday as high pressure slides over the west coast.
Extended discussion (Tuesday through Friday)
Pressure gradient will relax on Tuesday as broad troughing moves into place over the region and remains there through the end of the week. This will result in lighter winds. Valley highs will be near the 80 degree mark with mid 50s to low 70s in the mountains. Models hinting at the possibility at some precipitation skirting through far northern portions of the state by Friday, but details remain uncertain at this time.