textproduct: San Joaquin Valley

KEY MESSAGES

1. Extreme Heat will continue to be the major weather concern over the weekend and early next week. Extreme Heat Warnings have been issued and extended through Monday evening.

2. Persistent hot and dry conditions will also continue to promote the potential for wildfires with cured fuels.

3. Potential for thunderstorms over the Sierra Nevada crest continues for each afternoon through next week, with chances of 20 to 30% this weekend.

DISCUSSION

Strong pressure ridging dominates over Central California through at least Monday. Very hot and dry conditions prevail, with the exception of Sierra Nevada thunderstorms during the afternoons and evenings this weekend. Hotter temperatures will take place today and last until Monday, with peak heating expected on Sunday. We upgraded and extended our heat products until Monday evening. All areas that were under a Heat Advisory have been replaced with an Extreme Heat Warning; thus, our lower elevations are now under an Extreme Heat Warning. A 65 to 75 percent chance of a high of at least 105 degrees is shown for much of the San Joaquin Valley today and increases to 80 to 90 percent by Sunday. Readings of 110 degrees or hotter in the Valley are currently at a 15 to 25 percent chance, but with much of Kern County (including Bakersfield), at a 50 to 60 percent probability. As for the Mojave Desert, particularly the Indian Wells Valley, there is a 60 to 70 percent chance of a high reaching at least 110 degrees each day until Sunday, with chances decreasing to 25-35 percent beginning Monday. As flow remains south to southeast, additional monsoonal moisture will pass into our region through this weekend and bring a threat of Sierra Nevada thunderstorms. There is a 20 to 30 percent chance of afternoon/evening thunderstorms in the Sierra Nevada, mainly in the higher elevations towards the crest each day until Sunday.

We will see a gradual lowering of temperatures beginning Tuesday and a cooling trend continues into the remainder of next week. Triple digit heat persists, but highs will generally lower to 100 to 103 degrees for Tuesday and lower by at least a couple of degrees on Wednesday. More seasonal temperatures occur Thursday into next weekend, with the arrival of an upper-level trough passing over Northern CA and the Pacific NW. Afternoon highs largely in the 90s in the warmest locations of our forecast area. However, we will see an uptick in Sierra thunderstorms Wednesday and the remainder of the week due to instability and moisture. There is also a slight chance of thunderstorms to enter the Kern County mountains by then.

AVIATION

VFR conditions will prevail for the next 24 hours with light northwest winds during the day and variable winds overnight. Convection will have a 20-30 percent chance from 20Z Saturday until 04Z Sunday across the Sierra Nevada Crest.

FIRE WEATHER

Low minimum humidity will continue this weekend into Monday, with the Mojave Desert seeing 7 to 12 percent each day while the San Joaquin Valley and Sierra Nevada foothills remain in the teens. Overnight humidity recoveries will be moderate this weekend and improve by next week. Thunderstorm chances will occur mainly along the Sierra Nevada crest, or 20 to 30 percent today through Sunday and again by the middle of next week. There is also a 10 to 20 percent chance of thunderstorms into the Kern County mountains by the middle of next week. Isolated dry thunderstorms also exists for the Sierra Nevada crest each day through Sunday. Any fires that develop will have the potential for large plumes due to mixing heights of 9,000 feet and above.

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 Monday for CAZ300>317-319- 321-332-334>339.