September 14, 2017 – A few showers possible later today and tonight across the northern mountains as a cold front slides south. Cooler temperatures today, then readings return to around average for the weekend.
Dry weather has returned to the region. Temperatures are cooler ranging from the upper 30s in the mountain valleys to the 60s to around 70 in the Central Valley. Stronger onshore flow is bringing stratus inland into the southern Sacramento and northern San Joaquin Valleys.
Northern stream trough deepens along the West Coast today and pushes a cold front south later today and tonight. Showers and thunderstorms may develop along the front across the northern mountains and northern Sierra Nevada as it moves south. Cooling will continue to spread inland today as synoptic cooling increases and onshore flow continues.
Dry and milder weather returns for the weekend as the trough weakens across NorCal.
Extended discussion (Monday through Thursday)
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Models a bit out of sync in the extended forecast. Both the GFS and ECMWF show a trough pattern dominating the West Coast, but these models disagree as to how far south the trough will dig and how much precipitation is possible across NorCal. The ECWMF is more aggressive in bringing the trough over our CWA with good chances of precipitation for a couple days. The GFS limits moisture over NorCal and quickly pushes the trough to our east. Have kept the possibility of precip across the northern and Sierra portions of our CWA through midweek next week, though not as expansive coverage as the ECMWF suggests. Although precipitation coverage has lower confidence, we are confident in a significant cooling pattern. Daytime highs could range 10-20 degrees below normal by Tuesday (coolest day) and the Sierra could flirt with snow levels in the 7000-7500 ft range.