textproduct: San Joaquin Valley

KEY MESSAGES

1. Flood Watch in effect until Friday evening due to Slight (15-40 percent) risk of Excessive Rainfall across much of the region today and in the Sierra Nevada tomorrow. There is a marginal (5-15 percent) risk of Excessive Rainfall today in the northern portion of the Valley and Sierra Nevada and tomorrow in the east side of the Valley.

2. 15 to 30 percent chance of thunderstorms this afternoon through Friday morning across much of the region. 10-20 percent chance Friday afternoon in the Sierra Nevada and foothills, and a 5-15 percent chance in the San Joaquin Valley, Kern County mountains, and the Mojave Desert.

3. Temperatures rebound over the weekend into next week before another cooldown midweek.

DISCUSSION

This morning, showers began moving into our area from the remnants of Tropical Storm Mario. However, as the center of the low moves up the coast, it will bring more moisture into our area later this afternoon and evening along with the chances of thunderstorm. The rain amount from this storm especially overnight and during thunderstorms had led to the issuance of Flood Watches for most of the area through Friday evening. Burn scars are the major concern due to the heavy rain. There is a 15 to 30 percent chance of thunderstorms from this afternoon to Friday morning as the chances move from the Mojave to the Valley to the Sierra Nevada. The heavy rain has led to a Slight risk of excessive rainfall for most of the area.

Things begin to taper off Friday afternoon but the thunderstorm chances will remain through the evening. The Sierra Nevada is under a slight (15-40 percent) risk of excessive rainfall with the eastern half of the Valley under a marginal (5-15 percent) risk. Saturday through Monday, things dry out as temperatures climb as a weak ridge develops and the trough moves west. However, there remains a 5 to 15 percent chance of thunderstorms over the Sierra Nevada. Ensembles diverge Monday into the middle of next week regarding whether the cutoff low that will remain in the Pacific to the west will be picked up by a trough sliding in from the Pacific Northwest or if it weakens and the trough slides well north across Washington.

AVIATION

18Z Update:

Thunderstorm chances will creep in making most of its way in by around 0Z and will persist through 6Z before primarily being over the mountains and Mojave desert. Lower visibilities possible in heavier showers and lower clouds over the mountains. Otherwise, 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

Flood Watch through Friday afternoon for CAZ321-322-331>339. Flood Watch from 2 PM PDT this afternoon through Friday afternoon for CAZ304>316. Flood Watch through Friday evening for CAZ317>320-323>330.