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June 8, 2020 – Dry weather with a warming trend this week. Breezy northerly winds will bring a period of elevated fire weather conditions today. Cooler temperatures and possible precipitation chances return late this week.

Discussion

Skies have cleared out early this morning other than some high clouds spilling over the eastern Pacific ridge into NorCal, and some lingering low clouds along and east of the northern Sierra/southern Cascade crest. The northerly surface pressure gradient (MFR-SAC) has held around 5 to 6 mbs since last evening, and northerly gusts in the teens to mid 20s mph have been reported along the west side and north end of the Sacramento Valley, while local northeast gusts of 20-30 mph are occurring over the foothills and west slopes of the northern Sierra Nevada. KDAX VWP indicating 30 kt northerly winds from about 1-3k ft above the surface.

So far, stronger northerly breezes have been limited to areas along the western edge of the Central Valley. Expect the breeziness will become more widespread through the valley by mid- morning and continue into the afternoon as surface heating eliminates the radiative inversion. Winds expected to decrease late this afternoon and early this evening as gradients relax. Red flag warning remains in effect into this evening for the western portions of the southern Sacramento and northern San Joaquin valleys into the Delta region where the best combo of low RH and northerly breezes are expected.

Otherwise, dry and warmer weather is expected into Thursday as ridging builds along the West Coast. The warmest days are expected on Wednesday and Thursday when highs across the Central Valley are forecast to be in the lower to mid 90s. Overnight lows should cool into the low to mid 60s in most locations, providing overnight relief. Although these forecast highs are not expected to be as hot as recent events, sensitive groups could be impacted as some areas of moderate heat risk are indicated.

Extended Discussion (Friday through Monday)

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The forecast remains on track with a long wave trough moving into the region. By Thursday, the trough is knocking on the West Coast’s door bringing a more pronounced change in the weather pattern Thursday night into Friday. The Delta Breeze will make a return and influence the southern Sacramento and northern San Joaquin Valleys. By Friday, onshore flow becomes more dominant allowing high temperatures to fall back into the low 80s over most Valley and Delta locations. This will mark a 6 to 10 degree cool down relative to the previous day.

Besides the cool down, an increase in shower chances return on Friday into the weekend. The best chances are forecast to reside over the northern Sacramento Valley into the adjacent foothills and mountain locales. Depending on how far south the trough axis digs, some of this activity could spill farther south toward the I-80 corridor. The GFS continues to paint a wetter and farther south solution while the ECMWF is more conservative. Have opted to stick with the NBM guidance as seems more consistent and keeps precip confined mostly to the terrain and north end of the Sacramento Valley for Friday with chances seeping farther south along the Sierra for Saturday. Valley temperatures should be a few degrees cooler on Saturday before warming back up to the mid to upper 80s on Sunday.