textproduct: San Joaquin Valley

UPDATE

Updated Aviation Section.

KEY MESSAGES

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

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

DISCUSSION

A ridge of high pressure continues to dominate the area and will remain through the week leading to temperatures to continue to rise. In the Valley, we have a 25 percent chance or less of highs of at least 105 degrees today but it goes up to 25 to 50 percent for Sunday and Monday. Because of this a Heat Advisory is in effect for the Valley and foothills through Monday. In the Desert, an Extreme Heat Warning remains in effect as a 60 to 80 percent chance of highs of at least 110 today before being 10 to 25 percent chance through the week for most locations with the Indian Wells Valley seeing persistent 20 to 40 percent chances through the work week.

The ridge flattens a bit on Tuesday as a shortwave slides over in the Pacific Northwest. The probability of 105 degrees in the Valley drops to 15-30 percent beginning Wednesday through next weekend because of this. The Desert also slightly cools but will still have areas of major heat risk thanks to a 60 to 90 percent chance of highs of at least 105 into next weekend. The CPC continues to favor above average temperatures in the 6-10 and 8-14 day outlook with a 50 to 70 percent chance.

A concern this heating brings is that the minimum RH values will drop to the midteens to lower 20s for the Valley, Sierra Nevada and foothills and to the single digits in the Desert. While winds will largely be light and diurnal, the hot temperatures and low relative humidity brings about elevated concerns for fire weather, with ERCs (Energy Release Component) approaching the maximum so far this year. Downsloping winds along the Mojave Desert Slopes in conjunction with the high pressure will further highlight to risk for fire development, as there is a 70 to 80 percent probability for maximum gusts to exceed 35 mph on Monday.

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 11 PM PDT Monday for CAZ337>339. Heat Advisory until 11 PM PDT Monday for CAZ301>317-319-321- 332-334>336.