textproduct: San Joaquin Valley

KEY MESSAGES

1. Extreme Heat Warning issued for the Mojave Desert and Indian Wells Valley Thursday through Monday. Major HeatRisk expected with afternoon highs 108 to 112 each day.

2. Lingering monsoonal moisture will bring a slight chance for thunderstorms across the Sierra Nevada crest this afternoon, though lower probabilities exist compared to Tuesday.

3. High pressure over the region will maintain temperatures near season averages for the remainder of Central California for most of the week.

DISCUSSION

High pressure previously over the Great Basin region has shifted south and centered itself over central and western Texas today. The change in orientation of this system has affected the synoptic-level atmospheric flow over central California by changing the prevailing wind direction from the southeast to the southwest. The result is providing the region with less monsoonal moisture in the mid levels and, therefore, a lowered chance for thunderstorms across the Sierra this afternoon. There remains around a 15 to 25 percent probability today, however conditions will be more benign compared to Tuesday, and will continue to decrease through the weekend and next week.

In the latter part of the work week, the area of high pressure is expected to expand westward over the Four Corners and much of southern California. While impacts from the system will be fairly negligible for the San Joaquin Valley, hotter conditions are expected in the Mojave Desert. On Thursday, there is a 90 percent probability for maximum temperatures to exceed 105 degrees. Then, beginning Friday, there is a 60 to 70 percent probability for temperatures to exceed 110 degrees each day, with the greatest chances in the Indian Wells Valley, including the communities of China Lake, Inyokern, and Ridgecrest. With an 80 to 90 percent probability for minimum temperatures to exceed 80 degrees on Saturday in this area, there will be little relief from the heat without the help of air conditioning and a Major Risk for heat-related illnesses for much of the population. The Extreme Heat Watch previously issued for the Mojave Desert and Indian Wells Valley has been upgraded to an Extreme Heat Warning valid from Thursday, July 23rd to Monday, July 27th.

This pattern is favorable to continue through at least the end of the month, with ensemble guidance showing the aforementioned high pressure remaining firmly in place over much of the western United States. Through most of this period, there is at least a 50 to 60 percent probability for afternoon highs to exceed 100 degrees each day in the San Joaquin Valley.

AVIATION

VFR conditions will prevail in the San Joaquin Valley for the next 24 hours.

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 from 8 AM Thursday to 9 PM PDT Monday for CAZ337-339.