textproduct: San Joaquin Valley

KEY MESSAGES

1. Heat Advisory in effect for the San Joaquin Valley, Sierra Foothills and West Side Hills along the Coastal Range through 10 PM tomorrow night.

2. High probability (70 to 90 percent) for triple digit highs in the San Joaquin Valley tomorrow.

3. Medium chance (60 to 70 percent) for a wetting rainfall in the Sierra Nevada near Mount Whitney tomorrow afternoon.

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

DISCUSSION

The ridging that produced the triple digits across the Valley and Mojave Desert will strengthen slightly through tomorrow, leading to highs a couple degrees higher than seen today, as well as keep lows at night in the upper 60's into the mid 70's for the Valley and only cooling to into the upper 70's to around 80 degrees in the Desert, West Side Hills and Sierra Foothills overnight tonight. These conditions fall under the Moderate to Major Heat Risk categories, which affect much of the population without proper cooling like air conditioning.

This heat will be short lived, as the ridge causing it will be pushed east by an incoming trough, which will lower temperatures in the Valley into the mid to upper 80's by Sunday. As this trough moves through the region on Friday, tight pressure gradients with its leading edge will cause strong winds along the Mojave Slopes and breezy conditions for the Valley. Current probabilities for 45 MPH gusts along the Mojave Slopes is 50-75% on Friday, and 30-50% on Saturday. This system is also likely to be a dry one, so while temperatures will be cooler, so will dew points, making the relative humidities remain stable through the week. So with the breezy winds and low minRHs, fire risk may be elevated, even as we transition to the shoulder season.

After this weekend, the 500mb heights are expected to retain a trough-like pattern through much of the work week, though the intensity is expected to be reduced from what we are likely to see this Friday, meaning temperatures will rise slightly while remaining in the upper 80's by Monday, then remaining steady through at least next Thursday as the pattern keeps its shape.

The long term forecast is similar for the 6 to 10 day forecast, as the Climate Prediction has our area in likely near normal temperatures for that time period. This chances by the 8 to 14 day outlook, becoming leaning above normal for temperatures, meaning a new ridge may build in by that time period, though triple digits become less likely as we move deeper into September.

AVIATION

VFR conditions expected for the next 24 hours. A 5 to 15 percent chance of thunderstorm across the Sierra Nevada Crest around Mount Whitney from 19Z Thursday through 03Z Friday.

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 until 10 PM PDT Thursday for CAZ300>317-319-321.