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

3. Medium probability (50 to 60 percent) for measurable rainfall in the Sierra Nevada near Mount Whitney both Wednesday and Thursday.

4. Stronger winds expected to develop in the Mojave Desert Slopes later this week.

DISCUSSION

Slight amounts of lingering moisture from the remnants of Marie are pushing through southern California and portions of central California this morning, leading to scattered cloud cover over the Coastal Range and southern Kern Mountains. While some of this moisture is resulting in showers across the LA region, very little is expected for central California over the next few days. Locations with the best chances are the Frazier Park/Mount Pinos area and the Sierra Nevada around Mount Whitney. The first of these has a 30 to 40 percent probability to receive measureable precipitation (>0.01") each day through Thursday, and the latter with a 60 to 70 percent probability. In addition, the Mount Whitney area has a 30 to 40 percent probability to receive a wetting rain (>0.10"). However, all other locations of Central California have less than a 10 percent probability to observe measurable rainfall.

Over the next few days, a ridge of high pressure is projected to build in over California from the east, leading to warmer and drier conditions across the local area. By tomorrow, widespread Moderate Heat Risk with pockets of Major Heat Risk will encompass the San Joaquin Valley, Sierra Foothills, and West Side hills along the Coastal Range; NBM ensemble guidance gives a 60 to 70 percent probability for highs to exceed 100 degrees. The heat will expand across the Central Valley on Thursday, with more favorable probabilities at 70 to 80 percent and increasing areas of Major Heat Risk. A contributing factor to the Heat Risk level will be the morning low temperatures, which have a 40 to 50 percent prob to exceed 70 degrees in the valley; urban areas and the foothills along the thermal belt have stronger probabilities for 75 degree minimums at 60 to 70 percent.

The warming trend combined with dew points holding stationary in the low-to-mid 50s will result in a drop in relative humidities outside the Sierra Nevada. In the lower elevations, minRH values are expected between 20 and 25 percent, with desert values approaching 10 to 15 percent towards the end of this week. Sierra values will fall briefly today before improving midweek as mid- to-upper level moisture tracks across the region.

Later this week, a low pressure trough is projected to drop south into the contiguous US from the north Pacific and scrape through northern California. Flow across central California will turn to the west, resulting in a cooling trend back towards season averages. However, the strong pressure gradient associated with the low will result in gustier conditions to develop across the typically wind-prone locations of the local area. On Friday, there is a 70 to 80 percent probability for maximum wind gusts to exceed 45 mph in the Mojave Desert Slopes.

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.