textproduct: San Joaquin Valley

KEY MESSAGES

1. Temperatures drop drastically over the weekend into early next week.

2. High wind gusts over 35 mph are likely into Sunday night (65-80% chance) over the San Luis Reservoir with a Lake Wind Advisory issued.

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.

4. There is around a 50-70% chance for 72 hour snowfall greater than 2 inches above 9000 feet from Sunday into Wednesday morning.

DISCUSSION

The heat might be finally giving up the ghost despite highs being in the 90s. A spooky looking trough will begin to slide in overnight bringing in cooler air and making it really fall-like. Saturday brings a 35 to 50 percent chance of highs of 85 degrees or higher for most of the Valley south of Merced County. The trough also brings an increase in winds. A Lake Wind Advisory is currently in effect for San Luis Reservoir through Sunday evening.

Sunday continues the cooling trend with a 50 to 60 percent chance of highs of at least 75 degrees south of Merced. However, the first real precipitation of the water year is expected mostly in the southern portion of the Sierra Nevada and the Mojave Desert thanks to some of the moisture from Tropical Storm Rachel. The Valley can see a 20 percent chance or less of a tenth of an inch of rain total with this system. The central Sierra and foothills see a 20 to 35 percent chance of a tenth of an inch on Sunday while the southern Sierra has a 50 to 60 percent chance. The Desert will be far from bone dry with a 45 to 65 percent chance of a quarter of an inch of rain.

Monday will be the coolest day of the week with highs at a 65 to 75 percent chance of 70 degrees or lower. However, precipitation chances increase for the entire Sierra Nevada to a 30 to 50 percent chance of a tenth of an inch even up to Yosemite. Snow levels also decrease to 7,000-7,500 feet overnight into Monday. There is a 50 to 70 percent chance of 2 inches of snow above 9,000 feet Sunday through Wednesday while there is a 50 to 70 percent chance of just a dusting between 7,000 and 9,000 feet.

However, the October heat returns like a zombie as a ridge of high pressure slides in the middle of the week and will persist into next weekend. High temperatures in the Valley have a 35 to 50 percent chance of reaching 90 degrees next weekend. The CPC highlights a 50 to 70 percent chance of above average temperatures in the 6-10 and 8-14 day outlooks. However, both outlooks also have a gradient from a 33 to 40 percent chance of below average precipitation in the northern portion of the Valley and equal chances of above and below precipitation Fresno southward.

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 11 PM PDT Sunday for CAZ300.