textproduct: San Joaquin Valley

KEY MESSAGES

1 Temperatures drop slightly Thursday and Friday before a significant decrease over the weekend.

2. Moisture tracking over the region in the late week period will bring a 10 to 30 percent chance of thunderstorms over the Sierra Nevada on Friday. 5 to 25 percent chance of precipitation Friday in the Valley.

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

4. Precipitation chances return middle of next week.

DISCUSSION

High clouds are beginning to make their way from the Pacific as well as the trough begins to slide in from the Pacific Northwest. This combination will help lower high temperatures on Thursday and Friday to most of the area as the Valley will see a 5 to 25 percent chance of triple digits. However, the trough will also pick up more moisture the remnants of Tropical Storm Iselle which will increase Sierra thunderstorm chances from 5 to 15 percent on Thursday to 10 to 30 percent on Friday. The Valley also sees a 5 to 25 percent chance of actual precipitation on Friday although it will be very small.

Temperatures drop even more Sunday into next week as a second trough slides in bringing in a 5 to 20 percent chance of highs of at least 95 degrees from Sunday through Wednesday in the Valley. Precipitation also returns with this second trough as latest ensembles show the trough picking up moisture from another tropical disturbance into the area. Ensembles currently show a 25 percent chance of any rain accumulating on next Wednesday and Thursday. The CPC is showing a 33 to 50 percent chance of above average precipitation in the area across the 6-10 and 8-14 day outlooks. However, the cooldown might not be as long as it shifts from a 33 to 50 percent chance of below average temperatures in the 6-10 day outlook to near normal to a 33 to 40 percent chance of above average temperatures 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

None.