June 19, 2018 – Anti-cyclonic flow beginning to take hold as the large upper low that brought the cool weather over the weekend has now drifted into Montana. Skies are mostly clear across the region early this morning and current temperatures are mostly milder compared to 24hours ago and generally range from the 40s in the mountain valleys to the upper 50s to upper 60s across the Central Valley (except 70s across portions of the northern Sacramento Valley.
Upper ridging progged to build through mid-week with dry weather and slightly above average temperatures. Light to moderate Delta Breeze expected to continue tempering the heat in the Delta and Sacramento region. Short-wave skirts far northern CA late Wednesday, but appears deeper convection will occur north of the forecast area (OR/CA border and north into the PacNW).
The hottest weather so far this season is forecast to begin Friday as high pressure strengthens and surface flow transitions to northerly. Highs through the Central Valley on Friday are expected to range from 100-105.
Extended discussion (Saturday through Tuesday)
High pressure ridging will bring hot weather to the area this weekend, peaking on Saturday. High temperatures for Saturday are forecast to be 12 to 17 degrees above normal, with 102-105 across the Central Valley, 93-103 in the foothills, 73-93 in the mountains.
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This will bring the potential for moderate to high heat risk, even for the general population in a significant portion of the Central Valley and the Delta and into the foothills. Sacramento is currently forecast to reach 105, which is one degree shy of the record of 106, set in 1988. Redding is also forecast to reach 105, which is well short of the record of 111, set in 2006.
Northerly winds and low humidity levels will increase fire danger over the weekend, especially on Saturday.
Sunday may be a little less hot as the ridge axis shifts eastward and flow shifts to more southwesterly. This will be felt most in the Delta and adjacent areas, as a Delta breeze brings some cooling later in the day and overnight. Monday is expected to see more cooling but continued above normal temperatures, with Valley highs generally in the 90s. Tuesday should be cooler yet, with temperatures closer to normal. So, the good news is this heat event will be relatively short.