Temperatures to plummet over the weekend, showers likely

September 27, 2019 – Much cooler weather along with a chance of showers and high elevation snow over the weekend into early next week. Below normal temperatures will continue through next week.

Discussion

Big change underway as offshore flow has reversed to onshore as ridge continues to flatten with the approach of the upper trough centered over the PacNW. Skies are clear across most of the forecast area, however marine stratus is quickly forming in the Sacramento region. Temperatures are cooler across the area compared to 24 hours ago and range from the 40s and 50s in the mountains to the 60s across the Central Valley.

Much cooler weather is on tap through the weekend into early next week as the deep trough settles into the region. By Sunday, highs will be running 25-35 degrees cooler compared to yesterday!

Most shower activity is expected to be over the mountains through the weekend, but a few showers will be possible in the valley and foothills as well. Some early season high-elevation snowfall will also be possible across the higher elevations of the northern Sierra Nevada and southern Cascade Range, with a few inches of accumulation possible over the higher passes.

Extended Discussion (Tuesday through Friday)

Upper trough axis shifts well into the Great Basin on Tuesday so precipitation threat should be over by the start of the extended period.

As this occurs, breezy north winds are likely at least through the morning hours. Should see a decrease in winds by the afternoon as high pressure aloft begins pushing in over the west coast. Despite the warming temperatures, daytime highs Tuesday are forecast to come in about 10 degrees below normal.

Temperatures warm just a little on Wednesday but still remain below normal as another Pacific trough moves into the Pacific Northwest. This system will hold daytime highs below normal through the end of the week as it passes by to the north of the CWA Wednesday through Friday. At this time, precipitation chances stay north of the CWA but minor deepening of the trough could bring some rain to the far northern zones around Thursday.