An extended period of dangerous heat expected for the holiday weekend into next week. Excessive Heat Watch from Saturday morning through Tuesday evening.
We are seeing southwest flow and quiet conditions today. Overall temperatures are within a few degrees of yesterday and we should see similar highs today as yesterday. We will then see gradual warming tomorrow with stronger warming Thursday and Friday as the western US ridge builds west into NorCal. This is going to bring an extended period of hot weather with highs 100+ through the holiday weekend. Highs Thursday and Friday will range from 98 to 108 in the Valley and foothills with 80s and 90s in the mountains. Overnight lows will also start to come up and will be on the warm side.
Extended Discussion (Saturday through Tuesday)
Ensemble guidance and cluster analysis continue to indicate strong anomalous ridging strengthening over the region this holiday weekend and into early next week. The ECMWF EFI suggests anomalous heat during this time frame. This will result in very dangerous heat given 1) extreme afternoon highs, 2) oppressive overnight lows and 3) long duration heat. Daytime highs between 100 to around 113+ degrees are expected in the lower elevations; hottest days Sunday and Monday. All time September high temperatures could be broken and we could even come close to all time high temperatures in some areas. Overnight temperatures will provide little to no overnight relief from the heat with lows ranging from the upper 60s to 70s in the Valley and 70s and 80s in the foothills; warmest lows Saturday and Sunday nights. As such, widespread high to very high heat risk is anticipated across interior NorCal, impacting the entire population.
An Excessive Heat Watch remains in effect from Saturday morning through Tuesday evening. Those with outdoor plans should plan accordingly to prevent heat-related illnesses. Drink plenty of water, stay indoors, and learn the symptoms of excessive heat exposure.
The extended period of very hot and dry conditions will bring elevated fire weather concerns. Know your wildfire risk and have an emergency plan in advance.