textproduct: San Joaquin Valley

UPDATE

Updated Aviation Section.

KEY MESSAGES

1. Extreme Heat Warning in effect for the Mojave Desert and Indian Wells Valley through Monday. Major HeatRisk expected with afternoon highs 108 to 112 each day.

2. A small increase in monsoonal moisture will bring a slight chance for thunderstorms across the Sierra Nevada crest again this Friday, but the rest of the week into next will see chances less than 10%.

3. High pressure over the region will maintain temperatures near season averages for the remainder of Central California before hotter conditions appear late next week.

DISCUSSION

High pressure continues to dominate over the Four Corners, leading to a brief increase in monsoonal moisture that may lead to thunderstorm development tomorrow afternoon, though previous afternoons with said moisture did not produce significant cells. But the current chances are 20-35% along the crest, mainly in Tulare County and southern Fresno County, so thunderstorms may still develop during that time. Looking beyond Friday, thunderstorms chances appear to drop off a cliff (less than 10% each afternoon) as the ridge moves further west, cutting off our area from incoming moisture from the Gulf of California.

As the ridge retrogrades west, temperatures in the Desert will remain high through at least Monday, but may increase again late next week. As for the San Joaquin Valley highs will be mainly fluctuating around 100 degrees, rising above or dropping below depending on the position of the ridge. But confidence is increasing for the ridge to move further over Arizona and into eastern California by late next week, placing Central California closer to the axis of the ridge, leading to increasing temperatures. Current chances for highs in the Valley of 105 degrees for next Thursday are 30-40% from Fresno southwards, increasing through the following weekend to 45-65%. Along with these increasing temperatures will be higher Heat Risk, with the Valley seeing growing chances for Major Heat Risk beginning on next Thursday and into that weekend, as well.

This pattern looks to hold through the long term forecast as the ridge remains in place into the beginning of August. The Climate Prediction Center is also seeing this pattern, as they have all of California under likely above normal temperatures from day 6 through day 14, as well as highlighting the Valley for a high risk (>60%) for hazardous temperatures on July 31st into August 1st, and at least a slight risk (20-40%) through the 6th of August.

AVIATION

A 10-25% chance of afternoon thunderstorms along the Sierra Nevada Crest from 20Z Today through 03Z Saturday. Otherwise, VFR conditions will prevail 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

Extreme Heat Warning until 9 PM PDT Monday for CAZ337-339.