textproduct: San Joaquin Valley

KEY MESSAGES

1. Temperatures will remain at or below season averages through next week.

2. Slight chance for showers across the Sierra Crest this afternoon. Diminishing chances into the weekend.

3. Breezy conditions over typical wind-prone areas including San Luis Reservoir, Lake Isabella and the Mojave Desert Slopes this afternoon.

DISCUSSION

This morning, a low pressure trough is located just off the Pacific Coast, which is pushing cooler, drier air into central California. The previous push of monsoon moisture has tracked further east as the trough has progressed over the previous few days, causing the shower and thunderstorm threat to shift to the Great Basin and Four Corners region. However, lingering moisture across California will bring a slight (ten to fifteen percent) probability for thunderstorms to the Sierra Nevada crest this afternoon. This is primarily due to warm upsloping air from the Central Valley lifting the moisture further into the atmosphere as it rises along the local terrain. For much of the region, the trough will bring welcome relief from the heat; afternoon highs today are expected to be their coolest since late June and five to ten degrees below season averages. There is just a 60 to 70 percent probability from the National Blend of Models for maximum temperatures to exceed 90 degrees across the San Joaquin Valley this afternoon. However, into the weekend, these probabilities rise as the trough begins to break down, resulting in more stagnant air being present aloft. Though in the meantime, the onshore push will bring a few breezy conditions to typical wind-prone areas such as San Luis Reservoir, Lake Isabella, and the Mojave Desert Slopes in the lee of the Tehachapi Range.

Early next week, a ridge of high pressure currently centered over the southern United States is anticipated to retrograde westward, building over the Desert Southwest. This will lead to the aforementioned warming trend for central California. However, temperatures are expected to remain near season averages for much of the next week.

The added moisture and relatively cool temperatures today will cause minimum relative humidity values to remain in the 30 to 40 percent range for the San Joaquin Valley and Sierra Nevada, and near 50 percent for the Sierra Foothills; desert values will remain between 10 and 20 percent from lack of moisture influence. The warming trend into next week will lower minimums near 15 to 25 percent in the valley and mountain areas, however moderate to good overnight recoveries at 50 to 60 percent will limit significant fire weather concerns.

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.