Key Points - Long-duration, dangerous heat event through early next week, impacting holiday outdoor events.
- Excessive Heat Warning remains in effect for the Valley, Delta and foothills through 11 PM Tuesday.
- Heat Advisory remains in effect for the Sierra, southern Cascades, and Burney Basin from 11 AM today until 11 PM Tuesday.

Discussion
It's going to be hot, hot, and then more hot as this dangerous, long-duration heat event continues through early next week.
Saturday will be the hottest days of this heat event with forecast highs of 105-118F. The NBM indicates a 80-100% chance of high temperatures 110 deg F or higher across the northern and central Sacramento Valley, and a 25 to 60% chance in the southern Sacramento and northern San Joaquin Valleys today into Saturday.
Overnight temperatures will provide little to no relief from the heat with lows in the upper 60s to mid 80s; warmest in the thermal belt regions of the foothills. As a result, widespread Major with areas of Extreme HeatRisk will be present across the Valley, foothills, & mountains through the weekend.

An Excessive Heat Warning remains in effect for the Valley, Delta, and foothills until 11 PM Tuesday.
Additionally, a Heat Advisory remains in effect for the Sierra, southern Cascades, and Burney Basin until 11 PM Tuesday. It is imperative for people to wear sunscreen, avoid the hottest part of the day (10 am to 7 pm) and stay in the shade while outdoors. If it's too hot for you, it's too hot for your pets. Make sure they have ample access to water, shade, and ALWAYS look before you LOCK. NEVER leave kids or pets in hot cars as temperatures will become LETHAL in a matter of minutes.

A strong upper-level ridge will begin to weaken and gradually slide southeastward towards the Great Basin by early next week allowing for southwesterly flow aloft and weak troughing to develop on the backend of the high. Temperatures will being to cool slightly and weak, diurnal onshore flow returns to the region.
The National Blend of Models (NBM) indicates a 30 to 70% chance of temperatures 105F or greater throughout the Valley, with 80 to 100% chance in the northern Sacramento Valley & foothills next week.

The extended period of very hot and dry conditions will bring elevated fire weather concerns to the Valley and foothills.
Minimum relative humidity values will be in single digits to teens each day this week (15-25% near the Delta). Know your wildfire risk and have an emergency plan in advance.



.EXTENDED DISCUSSION (Tuesday THROUGH Friday)...
Ensemble guidance and cluster analysis support the continued southeastward movement of the upper level ridge and development of weak troughing on the backend. The cooling trend will continue through next week. HeatRisk will be in the Moderate category for most of the Valley and Delta, with areas of Major and Extreme HeatRisk across portions of the northern Sacramento Valley and foothills. Valley highs will range from 100-110 deg F with cooler overnight lows in the upper 50 to mid 70s, with cooler temperatures in the Delta. Additionally, occasionally breezy afternoon onshore winds (15 to 25 mph) will contribute to an added cooling effect, especially around the Delta where temperatures will be several degrees cooler compared to more inland locations.
Despite this expected cooling trend, daytime relative humidities will still be in the single digits to mid teens combined with hot temperatures which will lead to elevated fire weather concerns Valley and foothills.




AVIATION
VFR conditions prevail next 24 hours across interior NorCal.
Generally light winds less than 12 kts expected for most areas.
Although increasing south to west winds are anticipated after 21z in the Delta and vicinity, with occasional gusts to 20 kts possible through 06z.




STO WATCHES/WARNINGS/ADVISORIES
Excessive Heat Warning until 11 PM PDT Tuesday for Carquinez Strait and Delta-Central Sacramento Valley-Motherlode-Mountains Southwestern Shasta County to Western Colusa County-Northeast Foothills/Sacramento Valley-Northern Sacramento Valley-Northern San Joaquin Valley-Shasta Lake Area / Northern Shasta County- Southern Sacramento Valley.

Heat Advisory until 11 PM PDT Tuesday for Burney Basin / Eastern Shasta County-West Slope Northern Sierra Nevada-Western Plumas County/Lassen Park.