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 80 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. Moisture will also bring a 20 to 30 percent probability for a hundredth of an inch of rainfall to the northern San Joaquin Valley on Friday.

DISCUSSION

Waking up this morning, I was struck by how wonderful it felt outside. It was nice and cool. Sadly, those early morning low temperatures will continue to just be a brief reprieve from the heat. The high pressure continues to remain in place over the Four Corners region, as such, our heat advisory for the Central Valley and the Extreme Heat Warning for the Mojave Desert will remain in place. However, a low pressure trough is currently off the coast of the Pacific Northwest and models are showing it beginning to move on shore by the end of the week. Until then, the Central Valley will continue to have temperatures in the 100s. The Probability of Exceedance (PoE) of 100 degrees today through Wednesday is 80-95% for the Valley. The PoE of 105 is 50-75% for the same time frame. So the San Joaquin Valley can expect temperatures in the low to mid 100s for the next few days.

Sweet relief from the heat will come mid to late this week as the low pressure begins its trek on shore. This will help break down the high pressure and bring normal to slightly below normal temperatures. By Friday, it'll still be in the 90s in the San Joaquin Valley, but there's only a 10% chance of exceeding the 100s. There will also be a slight surge of moisture as well thanks to moisture from Tropical Storm Iselle being transported into the jet stream. By Thursday, there is a signal for rain to start making an appearance in the highest elevations of the Sierra Nevada Mountains. By Friday evening, there's a 50-70% chance of rain greater than .01", in Madera, Merced and Oakhurst, there is a 16-37% chance of the same amount of rain in the same time frame.

Getting further out into the extended forecast, the trough will continue to influence temperatures. Sunday, there's a 14% chance of exceeding 100 degrees in Bakersfield. By Monday, only the Mojave Desert has chances to exceed 100 degrees. This is agreed with by the CPC, as their 6-10 day outlook has a 33-40% chance of below normal temperatures.

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.