textproduct: San Joaquin Valley

UPDATE

Updated aviation section.

KEY MESSAGES

1. Cooler Juneteenth and Saturday temperatures until warming temperatures start again on Sunday. Triple-digit heat expected by next Tuesday.

2. Hot and dry conditions next week will create increased fire risk across the region.

3. 15-25% probability for thunderstorms in the Sierra Nevada, including isolated risk for dry lightning.

4. Practice safety around lakes, rivers, and streams, as water is still running cold.

DISCUSSION

Temperatures will continue to slightly cool through the Juneteenth holiday into Saturday, with highs in the Valley likely lowering below 90 degrees by that day. This is due to a weak trough moving through the west coast, bringing down the 500mb heights aloft. As this comes ashore, afternoon RH's in the Valley are expected to improve into the 25-35% range both tomorrow and Saturday, however the Mojave Desert will still be in the teens to single digits. Juneteenth will also see a 15-25% chance for thunderstorms along the Sierra Nevada crest again, similar to what was seen this past afternoon with the highest chances around Yosemite NP. There is also a risk for dry lightning with these cells, so fire risk remains elevated in that area.

Looking to next week, the weak trough is expected to transition to zonal flow before ridge building begins by Tuesday, leading to a steady rise in temperatures and a return to the usual summer dryness for the Valley. Triple digits will make their return by Tuesday due to that ridge building and are forecast to continue into late next week. These temperatures are likely to carry on into the following week as the Climate Prediction Center continues to put Central California under leaning to likely above normal temperatures for the 6 to 10 and 8 to 14 day outlooks.

AVIATION

VFR conditions expected across the area for the next 24 hours. 15-25% probability for thunderstorms across the Sierra Crest this afternoon, particularly for the central Sierra and around Yosemite National Park.

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

Lake Wind Advisory until 5 AM PDT early this morning for CAZ300.