textproduct: San Joaquin Valley

KEY MESSAGES

1. Temperatures will remain about 10-15 degrees above normal through the end of the week before a significant cool down this weekend.

2. A Heat Advisory remains in place today and tomorrow throughout the Central Valley with a widespread Moderate Heat Risk.

3. There is a marginal risk for excessive rainfall in the Mojave Desert and along southern portions of the Sierra Nevada mountains this coming Sunday.

DISCUSSION

The heat pattern continues throughout the area with temperatures likely to remain about 10-15 degrees above average through the end of the work week. A strong ridge that remains in place throughout our region will likely begin to move out of the area this coming Friday, resulting in a significant change in the overall weather pattern. Looking at the weather pattern over the next couple of days, high temperatures will remain above 95 degrees today and tomorrow (85-100% chance) with a widespread Moderate Heat Risk remaining in place. A Heat Advisory therefore has been issued throughout the Central Valley for today and tomorrow. There is a small hint of cooler weather to come on Friday, but only a small hint, with the probability of temperatures above 95 degrees at about 45-60%. The widespread Moderate Heat Risk in place today and tomorrow will not be nearly as widespread on Friday, with a Moderate Heat Risk remaining likely in the southern Valley, but throughout the majority of the Central Valley there is about a 50% chance or less for a Moderate Heat Risk. Hence, the Heat Advisory that was in effect for Friday has been pulled back to now only include today and Thursday.

A variety of computer models and the majority of ensemble members indicate that a deep trough will move into our area this coming weekend off the Pacific Coast, resulting in fairly high confidence in a significant change in the weather pattern. By Saturday the probability of temperatures exceeding 90 degrees is reduced to almost 0% throughout the entire area excluding specific locations in the southern Central Valley where probabilities are higher. By Sunday temperatures are likely to remain below 80 degrees (85-100% chance) and this pattern of cooler temperatures will likely remain in place through the middle of next week.

In addition to cooler temperatures there is the possibility of precipitation this coming weekend into early next week as the remnants of Hurricane Rachel potentially impacts our area. The exact track of this storm is still uncertain so there is a lot of uncertainty with regards to exact rainfall amounts this far out. The Weather Prediction Center (WPC) has the Mojave Desert and localized areas along the Sierra Nevada in a marginal risk for excessive rainfall this coming Sunday. The most likely scenario would be for little to no rainfall in the Central Valley, with the Probability of exceeding (POE) .1 inch only at about 30-45% from this coming Sunday into early next week. However, much higher probabilities of rainfall exceeding .1 inch remain in place over the Mojave Desert and along the Sierra Nevada mountains (60-75%).

The Climate Prediction Center (CPC) 6-10 Day Outlook has a most likely scenario of us seeing near normal temperatures for this time of year and near normal precipitation. The 8-14 Day Outlook has us with a 40-50% chance of above average temperatures for this time of year and a 33-40% chance for below normal precipitation.

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

Heat Advisory until 10 PM PDT Thursday for CAZ300>322.