textproduct: San Joaquin Valley

KEY MESSAGES

1. Heat Advisory remains in effect for the San Joaquin and Kern River Valley until 11 PM Tuesday.

2. Widespread Moderate Heat Risk, including triple-digit heat, in the lower elevations until Wednesday. Some pockets of Major Heat Risk, particularly near urban areas.

3. Hot and dry conditions will create increased fire risk across the region this week.

4, 10-15% probability for thunderstorms in the Sierra Nevada the next few days, which may include dry lightning.

5. Practice safety around lakes, rivers, and streams, as water is still running cold.

DISCUSSION

Hot and dry conditions will prevail over central California for Tuesday and Wednesday as high pressure and stagnant air remains stationary over the southwestern United States. Afternoon temepratures across the region are expected to be around ten degrees above averages for this time of year during this time; triple-digit heat is anticipated for the lower elevations of the region. The warmer-than-average temperatures across the area will continue to result in dry conditions, with minimum relative humidity values in the San Joaquin Valley between 15 and 20 percent through Friday, and values 10 to 15 percent in the Mojave Desert. Some of these lower relative humidities will also creep into the higher elevations of eastern Kern and Tulare County, especially for the Lake Isabella area and the southern Sierra Nevada. This continues the risk for grass fire developments across the region, however the high pressure overhead will limit wind speeds, with locally diurnal and terrain processes being the dominant sources for surface winds.

There is a slight chance (10 to 15 percent) for isolated thunderstorm activity over the Sierra crests each afternoon due to the warmer temperatures from the valley and foothill areas rising above cooler conditions at the higher elevations. Any thunderstorm that develops can have cloud-to-ground lightning, intense rainfall rates, gusty and erratic winds, and small hail associated with them. A

s the mid-to-late week period approaches, ensemble cluster analysis suggests a weak low pressure trough will approach the California coast, moving into the local area early this weekend. The warmer valley temperatures interacting with an influx of low-to-mid level moisture will bring stronger thunderstorm chances for the Sierra on Thursday, with current chances standing at 15 to 20 percent from Yosemite National Park to Sequoia National Park. In addition, the trough will result in a cooling trend for the region, with afternoon temperatures at or a handful of degrees below average. For much of the San Joaquin Valley, there is only a 20 to 30 percent probability for maximum temperatures to exceed 90 degrees this coming Saturday.

Temperatures will begin to warm again in the late weekend into early next week as high pressure gradually builds in once again.

AVIATION

VFR conditions expected in the San Joaquin Valley 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 11 PM PDT Tuesday for CAZ300>321-332.