textproduct: San Joaquin Valley

KEY MESSAGES

1. Extreme Heat will continue to be the major weather concern over the coming week. Extreme Heat Warnings and Heat Advisories have been extended through the upcoming weekend to account for this.

2. Persistent hot and dry conditions will also continue to promote the potential for wildfires with cured fuels.

3. Potential for thunderstorms over the Sierra Nevada crest increases tomorrow afternoon and continues for each afternoon through the week, peaking this weekend with chances of 10 to 20%.

DISCUSSION

As high pressure continues to dominate the pattern aloft, hot temperatures will be maintained through at least the weekend and likely into mid next week. The current heat warnings and advisories will be in effect through Sunday night due to the widespread areas of Major Heat Risk across the Valley and Mojave Desert, which affects much of the population that do not have adequate cooling, especially overnight. Along with these temperatures, low RH's across the region (mid to low teens for the Valley and single digits in the Desert) will continue to keep the risk of fire elevated through the week.

A small amount of monsoonal moisture may make it further west and lead to some isolated thunderstorms along the Sierra Nevada crest, with chances of at least 5 to 15% beginning tomorrow, reoccurring each afternoon through the next 7 days and peaking over this weekend at 10 to 20%. There is also a 10% chance for dry thunderstorms over the crest on Saturday as per the Storm Prediction Center.

Looking the the long term forecast, a possible trough is currently being forecast to move over the west coast by mid next week, leading to a slight cooldown for the region. Something to note about this trough is the models continually pushing back when it will actually move in, keeping it confined to day 8 and beyond. This weakens the timing confidence even as the models continue to reach that outcome. This change will continue to be monitored as we look for relief to these hot temperatures.

AVIATION

VFR conditions will prevail for the next 24 hours with light northwest winds during the day and variable winds overnight.

AIR QUALITY ISSUES

None.

CERTAINTY

The level of certainty for days 1 and 2 is high. The level of certainty for days 3 through 7 is medium.

Certainty levels include low...medium...and high. Please visit www.weather.gov/hnx/certainty.html for additional information and/or to provide feedback.

HNX WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning until 8 PM PDT Sunday for CAZ337>339. Heat Advisory until 8 PM PDT Sunday for CAZ301>317-319-321-332- 334>336.