textproduct: San Joaquin Valley

KEY MESSAGES

1. Widespread Moderate Heat Risk, including triple-digit heat in the lower elevations starting again by Tuesday following a slight cooldown through the weekend.

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

3. 15-25% probability for thunderstorms in the Sierra Nevada the next couple days, which may include dry lightning.

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

DISCUSSION

While warm and dry weather is likely to continue for Central California, a small cooling trend is expected to start tomorrow and last through Saturday. High temperatures in the Valley are expected to dip below 90 degrees by that day as well. This will be due to slight lowering of 500mb heights over the next few days as the ridge currently aloft breaks down and becomes a weak trough. This weakening will also encourage thunderstorm development along the Sierra Nevada crest tomorrow and Friday afternoons. Current chances during those times are about 15-25%, and they also have 5% chance to produce dry lightning around the Yosemite NP area tomorrow. This carries with it an increased fire risk for that region. RH's are expected to slightly improve, into the 25-35% range, as the troughing moves through the region, though only for the San Joaquin Valley on Saturday. The dry conditions will begin again by Sunday.

This weak troughing is expected to become zonal flow by Sunday, resulting in a warm-up in temperatures again, before another ridge builds in from the southeast. This will push high temperatures in the Valley back into the 100's by Tuesday, marking the return of Moderate Heat Risk for the region as well. Highs in the Mojave Desert are expected to reach the triple digits a day earlier and warm into the mid 100's by Tuesday. These above normal temperatures are likely to continue; the Climate Prediction Center has the 6 to 10 day and 8 to 14 day outlooks in the likely above normal temperature category.

AVIATION

VFR conditions expected across the area for the next 24 hours. 15-25% probability for thunderstorms across the Sierra Crest from 18Z Wednesday through 03Z Thursday.

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

None.