The National Weather Service has extended the Excessive Heat Warning for the Northern San Joaquin Valley, the Mother Lode and the Sierra Nevada below 4500 feet through Thursday 8 PM.
High temperatures from the central valley to the Sierra Nevada (including Yosemite Valley) range from 100 to 117. Overnight lows in the central valley and the Mother Lode range from the seventies to the low eighties.
Additionally, isolated thunderstorms are possible over the Sierra Nevada this afternoon and Tuesday. By Wednesday there will be an additional increase in thunderstorm activity as more monsoon moisture will move into central California from the south. Thursday (the Fourth of July) and Friday may see the best chances for thunderstorms.
Thunderstorms can produce dangerous cloud-to-ground lightning along with strong gusty winds, brief heavy rain and hail.
If you have outdoor plans this week in the Sierra Nevada, be prepared for an afternoon or evening thunderstorm. Campers, hikers and boaters should keep an eye on the sky and if threatening weather approaches, seek safe shelter or harbor.
Children, the elderly and people with chronic ailments are the most susceptible to heat-related illness. Heat exhaustion, cramps or in extreme cases heat stroke can result from prolonged exposure to these conditions. Pets and livestock are also vulnerable to heat illness and should be cared for properly.
Remember to drink plenty of fluids, stay in an air-conditioned rooom, stay out of the sun, check up on relatives and neighbors who might need assistance and reduce outdoor exposure.