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 80 to 90 percent probability of temperatures of 105 degrees or hotter with little overnight relief.

DISCUSSION

Above average temperatures and dry conditions prevail this week. Although, there is about a 5 to 10 percent chance of isolated thunderstorms along the Sierra Nevada crest today. The ridge of high pressure continues to rebuild over the Western U.S. with its center over the Four Corners and Rocky Mountains regions. Little change in the pattern takes place until at least the middle of the week. A Heat Advisory remains in effect for the San Joaquin Valley and the West Side Mountains south of Highway 198 until Wednesday evening. The valley portions include mainly Fresno County southward. The Extreme Heat Warning is also in effect for the Mojave Desert portions of Kern County until Wednesday evening with very hot daytime high temperatures and warm (70s to near 80 degrees) overnight lows. There is an 80 to 90 percent chance of highs reaching at least 100 degrees in southern and western portions (Fresno County southward) of the San Joaquin Valley, and a similar chance for highs to reach 105 degrees or hotter in the Mojave Desert through Wednesday. Some minor lowering of temperatures occurs later this week, but highs will remain in the triple digits in the hottest locations while a lowering of probabilities for highs at least 100 degrees in the Valley and 105 degrees in the Desert is shown on Thursday and Friday. Forecast guidance shows the upper-level ridge gradually weakening during this part of the week.

A more noticeable cooldown, or return to near seasonal temperatures, begins this weekend as a trough of low pressure passes over the Pacific Northwest. This will weaken the ridge and allow it to shift further eastward. Dry conditions remain in the region for the remainder of the forecast period, or until next Monday.

AVIATION

VFR conditions prevail 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 11 PM PDT Wednesday for CAZ337>339. Heat Advisory until 11 PM PDT Wednesday for CAZ304>316.