textproduct: San Joaquin Valley

UPDATE

Updated Aviation Section.

KEY MESSAGES

1. Triple digit heat continues for San Joaquin Valley and Mojave Desert. 40 to 50 percent for Major Heat Risk in the Southern San Joaquin Valley early next week.

2. 10 to 20 percent probability for extreme heat in the Mojave Desert ending next week and starting September.

DISCUSSION

High pressure over the Four Corners region has resulted in upper level flow over central California from the southwest, forcing temperatures into the upper 90s to near 100 across the lower elevations of the region. With minimal change expected to the synoptic pattern, these temperatures are likely to stick around through much of the upcoming week. Through Wednesday, there is an 80 to 90 percent probability for afternoon highs to exceed 100 degrees each day in the San Joaquin Valley. This level of heat will result in a Moderate Risk of heat-related illnesses to those sensitive to heat, such as older adults (65+), infants, athletes, outdoor workers, those without effective cooling, and those with chronic diseases; there is some risk to the general population. Meanwhile, in the Mojave Desert, there is at least a 60 to 70 percent probability for afternoon highs to exceed 105 degrees this Tuesday and Wednesday, leading to patchy areas of Major Heat Risk.

A weak low pressure trough will push through the Pacific Northwest region before the weekend, slightly degrading the strength of the aforementioned high pressure. Upper level flow will shift to the west from the southwest, resulting in slightly cooler, but still above average, temperatures. However, the high will maintain most of its strength over the desert areas, with an additional 70 to 80 percent probability for highs to exceed 105 degrees. During the same period, there is a 50 to 60 percent probability for morning lows to exceed 75 degrees. The combination of these warmer highs and lows in the desert will lead to more widespread Major Heat Risk with smaller areas of Extreme Heat Risk developing. The latter of these has a 10 to 20 percent probability to occur.

As has been the case for much of the latter half of the summer, the warmer temperatures will drive down the relative humidity across the region. Through most of this coming week, minRH values in the San Joaquin Valley will be between 15 and 25 percent and up to 30 percent in the Sierra Nevada; single digits will be present in the Mojave Desert.

AVIATION

VFR conditions prevailing 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

None.