textproduct: San Joaquin Valley

KEY MESSAGES

1. Moderate to Major Heat Risk on Tuesday and Wednesday.

2. Elevated (>25%) probability of thunderstorms along the Sierra Nevada remains through Wednesday.

3. Slow moving mountain thunderstorms can produce excessive rainfall.

DISCUSSION

The strong high pressure system over the Rocky Mountains producing record hot temperatures will begin to move westward back into California. Combined with our above-average humidity, warming temperatures will lead to a higher probability of moderate to major risk of heat illness Tuesday and Wednesday. Likewise, the combination of greater than 60% probability for afternoon highs above 105 in the San Joaquin Valley AND overnight lows in the 70s, a Heat Advisory is in effect from Tuesday at 11 AM until Thursday at 11PM. A brief cooldown is expected by the end of the week into the weekend.

While high pressure will build in our region, the area of low pressure remaining over the Pacific will continue to surge monsoon moisture into California. Besides hot valley-wide conditions, the other weather threat on Tuesday continues to be potential thunderstorms producing heavy rain, hail, and wind gusts over the Sierra Nevada. A 20-30% probability remains across the Sequoia and Yosemite National Park, increasing to greater than 40% probability along the crest of Fresno, Madera, and Mariposa counties. This threat (though 10-15% lower) will also remain through Wednesday, with little change to the regional pattern until the end of the week.

Climate Prediction Center (CPC) is indicating that the extended time frame of the 6 to 10 day period will remain on the warm side. Current CPC analysis has a 50-60 percent chance that temperatures will likely be above normal conditions.

AVIATION

High Sierra thunderstorms after 18Z Tue could lead to mountain obscuration through at least 03Z Wed. Otherwise, VFR is expected across the central California interior 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

Heat Advisory from 11 AM Tuesday to 11 PM PDT Thursday for CAZ301>303-305>307-309>317-319-321.