textproduct: San Joaquin Valley

KEY MESSAGES

1. Major Heat Risk for the Indian Wells Valley, Mojave Slopes and Desert, with an Extreme Heat Warning in effect through next Monday.

2. Prolonged heat is expected to affect the SJ valley and adjacent foothills this weekend into early next week with a Heat Advisory in effect from Saturday afternoon through next Monday.

3. Drier conditions will develop with the warming temperatures, leading to increased fire weather concerns into this weekend.

DISCUSSION

High pressure currently situated over the Four Corners region will begin building further into central and southern California over the next 24 hours. Due tho the increasing pressure over the region, temperatures will being to rise across the area, approaching five to ten degrees above season averages beginning Friday. These warmer temperatures will be most obvious in the lower elevations and foothills, with temperatures in the San Joaquin Valley having a 50 to 60 percent probability to exceed 105 degrees on Sunday, and in the Kern Desert which has a 60 to 70 percent probability to exceed 110 degrees. Due to the increased temperatures in the forecast, a Heat Advisory has been issued for the valley areas starting noon Saturday, August 1st through 11 PM Monday, August 3rd. An Extreme Heat Warning is now in effect for the Mojave Desert, also continuing until Monday evening. Morning lows in the desert in the mid to upper 70s will result in widespread Major Heat Risk for this area for the weekend.

The increasing temperatures across the region will also cause a strong drying trend for much of the area, even more so than has already occurred so far this season. Through the Central Valley and Sierra Nevada, minimum relative humidities are expected between 10 and 20 percent throughout the next week, with desert minRH values in the single digits. While lacking strong winds, there remains threats for large fire developments solely due to the hot, dry conditions that will be present over the area.

This heat event is expected to last until the middle of next week as the high pressure system remains mostly stationary over the southwestern United States. A slight erosion of the system is possible in the mid to late week period as a low pressure trough moving through the Pacific Northwest scours a bit of the high away. However, temperatures still have a 70 to 80 percent probability to remain in the triple-digits and will stay around two to four degrees above season averages.

AIR QUALITY ISSUES

Unhealthy for Sensitive Groups in eastern Tulare County and SJ valley portion of Kern County for today and Friday.

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 11 PM PDT Monday for CAZ337>339. Heat Advisory from noon Saturday to 11 PM PDT Monday for CAZ301>317-319-321-332-334>336.