June 14, 2019 – Cooling trend into Saturday, but more hot weather returns early next week. Isolated afternoon and evening thunderstorms will be possible over higher elevations of the Sierra Nevada through Monday.
The upper level shortwave which brought some thunderstorm activity in the evening is exiting to the southeast, with just some high clouds lingering over the area early this morning. Marine stratus are a little more than 2000 feet thick at Fort Ord now, and may be thick enough for some scattered/broken low clouds to spread through the Delta and into the Sacramento metro area. GOES Night Fog is showing some low clouds gradually moving east of Cordelia into the western Delta.
The Delta breeze continues to blow, though this will begin to weaken some later in the day as upper level ridging develops. Overall, high temperatures today should near to a little below what we saw yesterday.
Some thunderstorms could develop this afternoon along the Sierra crest, though they should be mainly south of Hwy 50 as the short wave shifts farther to the south.
Onshore flow is expected to increase again on Saturday as another short wave moves into NorCal with continued slight cooling most locations. There is a small potential for isolated thunderstorms in the afternoon for the mountains of western Tehama County, Lassen National Park and the Sierra crest south of I80 as the short wave moves into the area. As this feature drops to the southeast on Sunday, warmer air spreads back into our area leading to a return to more hot weather early next week as strong high pressure develops over the eastern Pacific. Sunday highs could peak at around 100 over the northern Sacramento Valley, then warm around another 3-5 degrees on Monday.
Extended Discussion (Tuesday through Friday)
Strong ridge of high pressure over the EPAC builds into NorCal, resulting in dry conditions and well above normal temperatures through midweek. Forecast highs will be in the upper 90s to around 106 across Valley locations through Wednesday.
Little overnight relief is expected with lows generally in the upper 60s to low 70s. As a result, long outdoor exposures could increase the chances for heat-related illnesses among sensitive groups (the very young and the elderly).
Ensemble guidance shows the eastern part of the upper ridge weakening as a trough moves into the Rockies late next week. As a result, slight cooling can be expected with Valley highs remaining in the 90s; less cooling over the northern Sac Valley.
The general pattern suggests periods of breezy northerly winds and increasing fire weather concerns next week.