June 13, 2019 – Cooling trend into Friday, but high temperatures remain above normal through next week. Afternoon shower or thunderstorm will be possible over the Coastal Range and mountains of Western Plumas County today, and over higher elevations of the Sierra Nevada through Monday.
Upper troughing over NorCal has increased onshore flow and is deepening marine layer. Strong Delta breeze in effect attm is advecting cooler marine air into the Sacramento Valley. Currently the marine layer is about 1400 ft thick at the Fort Ord profiler, and expected to continue to deepen. Could be some stratus intrusion into the Southern Sacramento Valley this morning, but given current depth of marine layer, it will be patchy and short lived. Moderate to strong Delta breeze will persist today resulting in significant cooling into the Sacramento Valley and Northern San Joaquin Valley. High temperatures this afternoon expected to be upwards of 20 degrees cooler in the Carquinez Strait and up to around 10 degrees lower in Delta breeze influenced areas of the Central Valley.
Remainder of interior NorCal will be under lower heights/thicknesses and should see max temps near to slightly cooler. Increased instability over the Coastal Range and mountains of Western Plumas County this afternoon will bring a slight chance of a shower or thunderstorm.
Upper trough shifts into the Great Basin Friday with upstream upper ridging along 120 W. Onshore gradient remains strong and Delta breeze will continue to bring low level CAA into the Central Valley. Friday expected to be the coolest day for most areas during upcoming seven day forecast period. Threat of an afternoon shower or thunderstorm is focused mainly over the higher elevations of the Northern Sierra Nevada tomorrow.
Moderate to strong onshore flow expected to persist Saturday resulting in little chance of max temps for Delta breeze influenced areas. Remainder of the forecast area should begin to see an upward trend in high temps that will continue into early next week. Slight chance of an afternoon storm near the Sierra Nevada crest will persist through the weekend into Monday.
Extended Discussion (Monday through Thursday)
Warming returns to the region early next week as ridging from the eastern Pacific extends into NorCal. Look for highs in the upper 90s to above the century mark across the Valley; warmest readings likely across the northern Sacramento valley. Daytime highs will peak on Tuesday, with possible widespread triple digits in the Valley. These forecast highs range from 5 to 15 degrees above normal for mid-June. By Thursday, some cooling is expected but highs will remain above normal.