Area Forecast Discussion

Logo_NWS.jpg

National Weather Service - San Joaquin Valley / Hanford, CA
Issued: Wednesday, August 26 2026 - 11:01 AM PDT

KEY MESSAGES... 1. Triple digit heat continues for the San Joaquin Valley this week. Moderate to Major Heat Risk expected with a Heat Advisory in effect through Wednesday evening, mainly Fresno County southward.

2. Extreme Heat Warning in effect for the Mojave Desert through Wednesday evening with Major Heat Risk expected. An 0 to 70 percent probability of temperatures of 105 degrees or hotter with little overnight relief.

3. Moisture tracking over the region in the late week period will bring a 10 to 15 percent chance for thunderstorms to the Sierra Nevada crest.

4. Air Quality Alert for Merced County through Thursday morning due to smoke from a local fire.

DISCUSSION... Today is the last day of the Heat Advisory and the Extreme Heat Warning. It is still forecasted to be quite hot in the Valley and the Deserts. The Probability of Exceedance (PoE) of 100 degrees is 80-100% today for the SJV and a PoE of 104 degrees is 10-25%, mainly for Merced and Fresno counties. The lower half of the SJV (south of Fresno county) will not exceed 104. The south SJV has a PoE of 102 of 10-20%. So, the Fresno and Merced areas will be between 100-104 degrees today and the rest of the valley will be between 100-102. The Mojave desert will be much hotter as they have an Extreme Heat Warning. The Mojave Desert (specifically Ridgecrest) PoE of 106 is 70%, but drops to 42% for temperatures exceeding 107 degrees. This drops to a 14% chance when looking at PoE for 108 degrees.

A pattern shift is in the forecast still. The trough off the Pacific Northwest coast is beginning to move on shore, but the Central Valley will not feel its affects until Thursday and more so on Friday. Moisture will be present, thanks to Tropical Storm Iselle being sucked into the flow. There is a 5-10% chance of thunderstorms in the Sierra Nevada crest on Thursday, which increases to 10-20% chance on Friday. Also on Friday, there is currently a 30-65% probability of 0.25" of rain or more in the Sierra Nevada crest. In Fresno and Merced counties, we are looking at a 5-10% chance of 0.10" or more of rain. These chances go down further south, with Bakersfield currently having a 0% chance of 0.10" of rain.

Heading into the weekend and next week, a second trough is looking to come through. This'll aid in temperatures staying low, which is in line with the CPC's 6-10 day outlook of 33-40% chance of below normal temperatures. The CPC is also looking at 33-40% chance above normal precipitation for the same time frame.

AVIATION... VFR conditions prevailing for the next 24 hours. Over Merced county, expect hazy and smokey conditions due to a fire north of the city.

AIR QUALITY ISSUES... The Valley Air District has issued an Air Quality Alert for Merced County from Tuesday morning through Thursday morning due to smoke from a local fire. Exposure to particle pollution can cause serious health problems: aggravate lung disease, cause asthma attacks and acute bronchitis and increase risk of respiratory infections. In people with heart disease, short-term exposure to particle pollution has been linked to heart attacks and arrhythmias according to the US Environmental Protection Agency. Children and elderly people are also more susceptible to consequences of high particulate levels. Stay indoors if possible. Avoid prolonged or strenuous outdoor physical activities to reduce the affect of unhealthy air. For current air quality go to fire.airnow.gov

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... Extreme Heat Warning until 11 PM PDT this evening for CAZ337>339. Heat Advisory until 11 PM PDT this evening for CAZ304>316.