textproduct: San Joaquin Valley

KEY MESSAGES

1. Heat Advisory issued for the San Joaquin Valley, Sierra Foothills and West Side Hills along the Coastal Range.

2. Medium to high probability (70 to 80 percent) for triple- digit highs in the San Joaquin Valley Thursday.

3. Decreasing confidence in precipitation Wednesday. Medium probability (40 to 50 percent) for measurable rainfall in the Sierra Nevada.

DISCUSSION

A gradual warm-up begins today across central California in the wake of a cut-off low pressure system. The center of this system is currently located over western Montana and will continue to track eastward over the northern Great Plains over the next few days, allowing a high pressure ridge to build in over the western United States in its place. As with most areas of high pressure, this system is driving the warming trend the local areawill experience through midweek. By Wednesday, widespread Moderate Heat Risk will encompass the San Joaquin Valley, Sierra Foothills, and West Side hills along the Coastal Range; NBM ensemble guidance gives a 50 to 60 percent probability for highs to exceed 100 degrees. Temperatures will peak on Thursday, with probabilities for triple-digits pushing to 70 to 80 percent in the valley areas. Meanwhile, there is a 60 to 70 percent probability for valley lows to exceed 70 degrees, and similar probs for greater than 75 degrees in the foothills, providing less relief at night. A Heat Advisory has been issued for the lower elevations of the Central Valley as a result, valid from 10 AM Wednesday, September 9th through 10 PM Thursday, September 10th.

Previous iterations of the forecast highlighted the potential for tropical moisture to track over central California from the remnants of Tropical Storm Marie. However, more confidence is being placed in the high pressure building further west, resulting in the aforementioned moisture largely remaining off the coast. There remains a 40 to 50 percent probability for measurable rainfall (>0.01"), and 30 to 40 percent for a wetting rain (>0.10") in the Sierra Nevada around Mount Whitney and near Mount Pinos. However, all other locations of central California have less than a 10 percent probability for any precipitation.

In the latter portion of the week and into the weekend, ensemble cluster analysis suggests a robust trough will scrape northern California, resulting in cooler westerly flow across central California. This pattern will bring temperatures similar to this past weekend, with just a 30 to 40 percent probability to exceed 90 degrees next Sunday in the San Joaquin Valley.

AVIATION

VFR conditions expected 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

Heat Advisory from 10 AM Wednesday to 10 PM PDT Thursday for CAZ300>317-319-321.