September 18, 2018 – Below average temperatures continue today, then warmer weather returns for the second half of the week. Patchy smoke and haze will continue, mainly locally over northern portions of Shasta County. The weather remains dry through the weekend.
Discussion
Clear skies across the region early this morning except for a few high clouds up by the Oregon border. Current temperatures are similar to those of 24 hours ago and range from the 30s in the mountain valleys to the mid 50s to lower 60s in the Central Valley. Weak trough today will give way to ridging the remainder of the week with temperatures rising to above average by Thursday with highs returning to the lower to mid 90s across the Central Valley. Northerly winds will lower humidity levels, especially over the northern Sacramento Valley and adjacent foothills potentially increasing fire weather concerns.
Extended Discussion (Saturday through Tuesday)
Broad westerly flow aloft will bring seasonably warm temperatures this Friday into Saturday. The pattern then begins to amplify as an upper ridge builds over the eastern Pacific. A longwave trough will deepen across the western US late this weekend or early next week in response. Previous model runs hinted at a possibility of precipitation across far northern CA over the weekend, this is now being kept farther north. Regardless, a cooling trend is likely through the extended period, the extent of which will depend on how far south the trough drops.