Not quite as hot this week with temperatures briefly returning to near normal during the middle of the week before heating up again late in the week. Late week warming trend will bring areas of Major Heat Risk Friday.

Moderate Risk for heat-related illnesses for pets, livestock, and those who are sensitive to heat, especially those without effective cooling and/or adequate hydration.


Leftover MCV (originating from the large thunderstorm complex over Sonora (northern Mexico) on Friday evening) embedded in the mid/ upper moisture plume coming up from the south has interacted with the strong incoming short-wave trough over the PacNW to generate sprinkles and light showers across NorCal overnight. A few lightning strikes also occurred late Sunday evening along the western edge of the Sacramento Valley. Most of the precipitation has been a trace, but a few rain gages have reported 0.01″ and one gage near Stony Gorge Reservoir picked up 0.14″.

High temperature loop for the week. Triple digits abound

A little stronger onshore surface pressure gradient is developing and is resulting in a moderate Delta Breeze, but while the marine layer is redeveloping, it remains very shallow (around 1k ft deep on profiler data). The combination of cloud cover and lack of any significant cooling yet from the Delta Breeze has allowed temperatures to remain very warm overnight. Current temperatures are mainly in the 60s and 70s over the mountains, and in the 80s to lower 90s across the Central Valley. Delta Breeze influenced areas are in the mid to upper 70s.

No real overnight relief except in the higher elevations

A modest cooling trend is forecast into mid-week as the strong upper ridge retreats to the east allowing a gradual return of onshore flow to reinforce minor synoptic cooling.

Elevated moisture/instability will be shunted to the south and east by westerly flow, so the thunderstorm threat will likely remain east of the forecast area after this morning’s early activity ends. Ridge begins to extend westward again beginning Thursday which will mark the start of another warming trend.

Extended Discussion (Friday through Monday)

Desert SW high expands NW over NorCal towards the end of the week resulting in another round of well above normal temperatures. Friday appears to be the hottest day with NBM forecasting highs from around 103 to 112 in the Central Valley, hottest in the Northern Sacramento Valley.

Major Risk for heat-related illnesses for pets, livestock, and much of the population, especially anyone without effective cooling and/or adequate hydration. Impacts likely in some health systems, heat-sensitive industries and infrastructure.  Friday: 70-100% chance of exceeding 100° F through most of the Valley; 45-85 % chance of exceeding 100° F in the foothills

Minor cooling trend then develops over the weekend into early next week as ridge axis shifts east and upper troughing in the EPAC builds inland. High temperatures however remain slightly above normal by Monday. Dry weather continues through the extended forecast period.