textproduct: San Joaquin Valley

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 70 to 0 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

The Moderate to Major Heat Risk continues to dominate the San Joaquin Valley and the Mojave Desert and Slopes on Wednesday and Thursday. The Valley is under a Heat Advisory through 11 PM Wednesday as there is a 65 to 95 percent chance of triple digits on Wednesday before decreasing to 40 to 75 percent on Thursday. The Desert is under an Extreme Heat Warning with a 95 percent chance of highs of at least 105 on Wednesday before it drops to 60 to 80 percent on Thursday. However, temperatures begin to drop into the weekend and significantly into next week as the ridge of high pressure weakens and moves east. In its place a trough slides in from the Pacific Northwest bringing in cooler weather. The Valley currently is expecting a 35 to 60 percent chance of highs of at least 90 next Tuesday and Wednesday.

Moisture increases with thunderstorm chances in the Sierra Nevada increasing to 5 to 20 percent on Friday. The Valley also sees a 25 to 45 percent chance of accumulating precipitation on Friday. The increased moisture is part monsoonal but also some of the moisture from what will remain of Tropical Storm Iselle in the Pacific Ocean. Thunderstorm chances will remain at 5 to 15 percent for the Sierra from Saturday into next week. The CPC favors a 33 to 40 percent chance of above average precipitation in the 6-10 and 8-14 day outlooks despite the seasonal average being near 0 for this time of year. The temperature outlooks shift from 33 to 50 percent chance of below average in the 6-10 day outlook to 33 to 40 percent chance of above average in the 8-14 day outlook.

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 Wednesday for CAZ337>339. Heat Advisory until 11 PM PDT Wednesday for CAZ304>316.