textproduct: San Joaquin Valley

KEY MESSAGES

1. Temperatures will remain about 10-15 degrees above normal through Thursday before a significant cool down Friday into this weekend.

2. A Heat Advisory remains in place until 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

Expect another hot day tomorrow, similar to today's. Record high maximum temperatures were tied or exceeded at Fresno and Merced today, with highs in the upper 90s to the century mark. Also, record high minimum temperatures were tied at Fresno and Bakersfield with lows in the lower 70s. The chances for highs to reach the triple digits in the San Joaquin Valley are at 15 to 25 percent for Thursday and 15 percent or less on Friday. Temperatures lower to the mid 90s by Friday, so we won't see a huge change but are at least beginning to head in the downward direction. This is thanks to the persistent ridge of high pressure finally weakening.

A more significant change in temperatures and the overall pattern begins this weekend. Near seasonal temperatures are in store for Saturday. Chances for precipitation also enter the forecast for Sunday into next week. Much cooler temperatures arrive Sunday, with a 20 to 30 percent chance of highs of 70 degrees or lower and a 60 to 70 percent chance of highs of 75 degrees or less, including over the valley and desert. This is due to an upper- level trough moving from the Pacific with another deeper trough digging southward from the Northwest by Sunday. While we will be much cooler, we will have to contend with some tropical moisture that is entrained into our region. This will be associated with now Hurricane Rachel, but it will have weakened to a Tropical Storm and pass to our southeast, mainly over northern Baja California and into the southeastern CA desert. Based on the latest National Hurricane Center's forecast cone, the most likely scenario is Rachel makes landfall as a tropical storm over northern Baja late Saturday night into early Sunday morning, and treks northeastward along the Colorado River Valley and eventually the AZ strip (northwestern part of the state) by late Sunday afternoon. On Sunday and Monday, we are carrying at least a slight chance of precipitation over much of the forecast area. The most favorable locations for heavier rain will be over the Mojave Desert in eastern Kern County and southern Sierra Nevada, as the Weather Prediction Center continues to show a marginal risk (5-15% chance) of excessive rainfall for at least Sunday. Snow levels also lower to around 9000 ft by Sunday and around 8K ft by Monday. Overall, this is a low to moderate confidence forecast for this particular period, but confidence in precipitation has been increasing with the last few model runs.

Cooler than average temperatures prevail until at least Tuesday of next week, while slight chances of precipitation remain over at least the mountains and desert. Drier weather returns by midweek while cooler temperatures continue. Chances for highs at 70 degrees or lower in the Central Valley are at 30-40 percent until Tuesday.

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.