textproduct: San Joaquin Valley

KEY MESSAGES

1. Minor Heat Risk through the weekend into Monday as temperatures cool to early fall normals. Temperatures climb beginning Tuesday.

2. Low pressure trough approaches California today, bringing cooler temperatures and a possibility for precipitation along the Sierra Nevada mountains.

3. Low but notable chances (10-20%) for thunderstorms across the Sierra Nevada Monday.

4. Lake Wind Advisories for Lake Isabella and San Luis Reservoir again from Sunday afternoon into Monday evening and morning respectively.

DISCUSSION

As the low pressure trough approaches Central California, winds are expected to increase from this afternoon through at least Monday evening and a small amount of moisture moving in from the Pacific may result in isolated showers and thunderstorms along the Sierra Nevada crest tomorrow afternoon. As of this morning, Lake Wind Advisories have been issued for both Lake Isabella and San Luis Reservoir. The Lake Isabella Advisory will be in effect starting at 1PM today and run through 7PM Monday, while the Advisory for the San Luis Reservoir will start at the same time and run through 7AM Monday.

Thunderstorm chances with this system are around 10 to 20% from 11AM through 5PM as of current model runs, along with a 20-35% chance for a tenth of an inch of rainfall during that time period, mainly in the higher elevations of the Sierra Nevada range. There is also a chance for a trace of snowfall above 9500 feet as snow levels decrease to that level by Monday afternoon.

This trough will also lead to a significant cooldown when compared to climatological norms, with highs in the Valley only rising into lower 80's on Monday as the axis of the trough swings inland over the region. But this cooldown is expected to be short lived, as a strong ridge is expected to build in over the Southwest beginning on Tuesday and sticking around through at least next weekend. This will cause temperatures to rise into the mid to upper 90's, about 10 to 15 degrees above normal for this time of year (normal in the Valley being lower to mid 80's). The Climate Prediction Center also has this ridge remaining somewhat in place through the week after this, as our CWA is under a 70-80% chance for likely above normal temps during the 6 to 10 day outlook and increasing to 70-90% for the 8 to 14 day outlook.

AVIATION

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

Lake Wind Advisory until 7 AM PDT Monday for CAZ300. Lake Wind Advisory until 7 PM PDT Monday for CAZ332.