Area Forecast Discussion

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National Weather Service - San Joaquin Valley / Hanford, CA
Issued: Saturday, April 20 2024 - 1:10 AM PDT

KEY MESSAGES... 1. High temperatures remain above average through Monday

2. There is a 10 to 15 percent chance of thunderstorms over the Sierra Nevada in Tulare and Fresno Counties this afternoon.

3. Cooling trend expected Tuesday through Friday

DISCUSSION...

We have a ridge of high pressure just off the Pacific coast with a weak shortwave trough which brought some thunderstorms to the SIerra Nevada on Friday afternoon sliding southeast and dissipating. However, the trough impacts can still be seen later today with the potential of thunderstorms over the Sierra Nevada again this afternoon. Latest model ensembles are in agreement that the ridge will move onshore and strengthen a bit over our area while flattening to our north due to a trough that is going to slide along the U.S.-Canada border. This ridge has helped warm temperatures and will continue warming through the weekend until Monday.

Thunderstorm probability for this afternoon is at about 10 to 15 percent in the Tulare and Fresno county portions of the Sierra Nevada with CAPE values peaking around 1000 J/kg. Lapse rates between 500 and 700 mb over the SIerra Nevada are around 7 to 8 C/km which indicates a heavy lean towards instability. The surface based lifted index is peaking around -5 to -6 C which is not common for the Sierra Nevada. These parameters along with the warming temperatures and leftover moisture make thunderstorms favorable for this afternoon.

Monday is expected to be the warmest day with the best probabilities for our first 90 degree day of the year. Most locations in the Valley south of Madera and Merced have a 35 to 50 percent probability of a high of at least 90 degrees on Monday with the exception of Reedley. Kern County locations including Delano and Bakersfield have the highest probability between 45 and 50 percent of a high of at least 90.

However, things change on Tuesday as the ridge moves east and a trough slides in from the Pacific coast bringing cooler temperatures. Model ensembles are in agreement that this trough will weaken before being absorbed by a second trough that will move across the Pacific Northwest Thursday into Friday which will strengthen the trough. By Friday, there will only be a 20 to 45 percent probability of high temperatures of at least 75 degrees across the San Joaquin Valley and foothills.

AVIATION... Kern County Desert may have less than VFR conditions until 12Z this morning due to blowing dust. Thunderstorms are possible between 18Z today and 3Z Sunday mainly in the Tulare and Fresno County portions of the SIerra Nevada. Otherwise, VFR conditions will 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... Wind Advisory until 4 AM PDT early this morning for CAZ338.