August 12, 2020 – Near normal temperatures are expected for Wednesday, followed by a significant warming trend with widespread triple digits this weekend. Above normal temperatures are forecast to continue into at least early next week.
Discussion
Infrared satellite imagery reveals mostly clear skies over the northern half of California with a well-established marine layer along the Pacific coastline. Onshore gradients are around 2.2 mb between San Francisco and Sacramento, down slightly from 24 hours prior when it was 3.1 mb. Temperatures this early morning are running several degrees cooler than this time 24 hours ago, and will likely translate over similarly to low temperatures this morning.
Main story over the next several days will be the warming trend heading into the weekend. Upper level ridge over New Mexico will gradually build westward by the end of the week. As a result, the region will experience day-to-day warming into the weekend with triple digit heat becoming widespread as early as Friday. Further warming is forecast on Saturday as heat risks reach the moderate to high levels for most communities in the Sacramento Valley and northern San Joaquin Valley. In fact, some locations in the southern Sacramento Valley such as Sacramento will be approaching daily record highs around Saturday.
The current forecast on Saturday calls for highs around 101-105 deg F in the southern Sacramento Valley / northern San Joaquin Valley, and 103-108 deg F in the northern Sacramento Valley, corresponding to about 8 to 15 deg F above middle August climatology. Overnight temperatures are forecast to remain warm with many Valley and adjacent foothill locations remaining in the 70s for Friday and Saturday nights. Consequently, an Excessive Heat Watch is out for parts of the Sacramento and San Joaquin Valleys for the weekend.
Extended Discussion (Sunday through Wednesday)
Hot conditions are expected through the extended period as ridging over the Desert SW expands into the region. Daily highs will reach the 100 to 105 degree range in the Valley Sunday into mid- week. Meanwhile, little overnight relief is expected as lows could stay in the upper 60s and 70s in the Delta, Valley and foothills; a few low 80s cannot be ruled out over the foothills. Widespread moderate heat risk is anticipated, with some areas of high to very high heat risk including the Sacramento metro area. Therefore, an Excessive Heat Watch remains in effect from Saturday afternoon through Sunday evening. Make sure to drink plenty of water, stay in an air- conditioned room, and never leave pets and children unattended in vehicles. Dry conditions continue through the extended period, except for a few showers or thunderstorms over the Sierra crest across portions of Alpine and Tuolumne counties.