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 Wednesday.

2. Prolonged heat is expected to affect the SJ valley and adjacent foothills with a Heat Advisory in effect through Wednesday.

3. Drier conditions will develop with the warming temperatures, leading to increased fire weather concerns for most of the week.

DISCUSSION

High pressure continues to drive temperatures well above normal across the region through this weekend. Highs in the Valley will be in the range of 104 to 107 through Sunday, while the Mojave Desert will see highs around 108 to 111. Along with these highs, low temperatures at night will continue to be elevated, with the Valley only cooling into the mid to upper 60's (lower 70's in the urban areas), and the Desert remaining in the upper 70's overnight. These factors produce a Major Heat Risk for much of these two regions through at least Sunday, which affects a majority of the population, especially to those with limited access to proper cooling overnight.

Along with this heat, RH's will continue to be in the teens for the Valley and Mountains, and into the single digits in the Desert through much of this week, resulting in a prolonged period of elevated fire risk for the entire region. One component, wind, will be limited due to the strong high pressure over the majority of the Southwest.

Looking to the long term forecast, an area of troughing may move in from the northwest, leading to a cooling trend that may begin by Monday into mid next week. This is also seen in the probabilities for triple digits during that time, which decrease from 80-100% on Monday to 20-40% by Wednesday, August 12th. But due to how far out these forecasts are, confidence is limited until these dates get closer and a clearer picture can be seen.

AVIATION

VFR conditions will prevail 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 until 8 PM PDT Wednesday for CAZ337>339. Heat Advisory until 8 PM PDT Wednesday for CAZ301>317-319-321- 332-334>336.