National Weather Service - Discussion

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Area Forecast Discussion

National Weather Service - San Joaquin Valley / Hanford, CA
Issued: Tuesday, June 15 2021 - 2:00 PM PDT

SYNOPSIS...A large area of high pressure will continue to build westward from the 4 corners region through Friday bringing dangerously hot, life-threatening temperatures. The heat will spread into the San Joaquin Valley by Thursday and continue through the Saturday. A slow cooling trend will take place Sunday through the middle of next week.

DISCUSSION...A large upper ridge of high pressure centered over the four corners region is maintaining dry conditions across our area with temperatures running around seasonal normals today. Satellite imagery is showing some high clouds pushing slowly northward from Socal into our area which will continue to spread northward tonight and result in scattered to broken high clouds across our area on Wednesday. Meanwhile, the large ridge is progged to build westward and strengthen over our area tonight and Wednesday resulting in temperatures warming to above normal levels across our entire area on Wednesday with afternoon highs expected to reach the triple digits in the San Joaquin Valley, West Side Hills and lower Sierra foothills. Temperatures will reach dangerously high levels across the lower Kern County Mountains where an Excessive Heat Warning will go into effect at 1000 am PDT Wednesday. An Excessive Heat Warning remains in effect for the Kern County Deserts where highs are expected to range between 107 and 112 Deg F today and rise by another 3-4 degrees on Wednesday. The high is expected to strengthen further on Thursday as it continues to build westward. This will result in even further warming across the San Joaquin Valley, West Side Hills and lower Sierra foothills with high temperatures across these areas expected to range from 105 to 110 DEG F. An excessive Heat Warning will go into effect for these areas at 1000 am PDT Thursday.

By Friday, heights and thicknesses are expected to rise even further. This will result in daytime temperatures near or above record levels across much of our area. Latest probabilistic guidance is indicating that Fresno has a 64 percent chance of exceeding it's all time record high for June 18 of 107 Deg F set in 2017 and an 11 percent chance of exceeding it's time record high June temperatures of 112 Deg F set on June 25, 1925 and on June 30, 1891. For Bakersfield, the latest probabilistic guidance is indicating that there is an 80 percent chance that it's record high temperature for June 18 of 106 Deg F set in 1945 will be exceeded. Little change in temperatures is expected on Saturday as the ridge is progged to keep a strong grip over the region. Morning lows are expected to be in the mid to upper 70s across much of the San Joaquin Valley both days and there is a good possibility that some record high minimum temperatures could also fall on Friday and Saturday. Some instability is expected over the Sierra Nevada on Thursday and Friday and along with a southerly flow aloft bringing in some high level moisture, a thunderstorm or two could pop up in the afternoon near the Sierra crest.

The medium range models are in fairly good agreement with breaking down the upper ridge Sunday through Tuesday as an shortwave trough approaches the Norcal coast on Sunday and moves inland on Monday and Tuesday. This will result in temperatures trending downward by a few degrees each day. By Tuesday, daytime temperatures are expected to remain below the century mark in the San Joaquin Valley with a dry westerly flow prevailing over our area.

AVIATION...VFR conditions can be expected throughout the central CA interior for at least 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 an/or to provide feedback.

HNX WATCHES/WARNINGS/ADVISORIES... Excessive Heat Warning until 8 PM PDT Saturday for CAZ198-199.

Excessive Heat Warning from 10 AM Wednesday to 8 PM PDT Saturday for CAZ195-196.

Excessive Heat Warning from 10 AM Thursday to 8 PM PDT Saturday for CAZ179>191-197.