Area Forecast Discussion

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National Weather Service - San Joaquin Valley / Hanford, CA
Issued: Saturday, May 31 2025 - 4:05 PM PDT

UPDATE...Updated Aviation.

KEY MESSAGES... 1. A Heat Advisory is in effect for the San Joaquin Valley, Kern River Valley, lower Sierra Foothills, and West Side Hills valid from 11 AM Friday through 7 AM Sunday.

2. Widespread Moderate to Major Heat Risk is expected across the lower elevations of the region.

3. A disturbance over the weekend will allow for the development of strong winds over the mountains and across the Eastern Mojave Slopes of the Kern County Mountains early next week.

4. Mountain thunderstorms are possible this weekend, with a potential for widespread mountain storms on Sunday.

DISCUSSION... Heat-wave has begun with triple digits expected across the San Joaquin Valley and the Kern Desert. With the high pressure ridge well in place over the West, confidence is high in reaching triple digit heat this afternoon. Will expect conditions to remain hot and mostly dry today as moisture surges northward over the next few days. The moisture surge will allow for increasing convection over the district and showers and thunderstorms will spread across the area ahead of the next disturbance on around Sunday. Dry and comfortable conditions expected in the wake of the disturbance early next week before the start of the next warming trend into the latter part of the week.

Ensemble Probability of Exceedance (PoE) of reaching 100 degrees Today sits at 80% or above. 105 degrees will be more of a challenge today as PoE of 50% sits around the Huron/Lemoore area. Outside of that area todays PoE of 105 degrees has percentages between 25% and 40% with the higher end percentages on the west-side and south-end of the valley. Therefore, still have good confidence that the heat advisory criteria will be met on this afternoon.

Ensemble mean upper-air analysis is showing another disturbance crossing the region as the heat-wave comes to an end on Sunday and winds increase over the favored locations. While westerly winds will increase on Sunday, PoE of wind gusts reaching 35 mph is only 35%-40% over the favored locations. Outside of the wind-prone areas, expect 15-25 mph wind gusts during disturbance passage. While still a fire weather concern, the breezy winds will help limit the heat and the northwesterly extension of the moisture plume into the area. Will expect convection this weekend over the Sierra Nevada as Probability of Thunder sits around 20% and continue into Monday with Probability of Thunder then at 30%. By Tuesday, the disturbance pushes further away with diminishing dynamic and moisture to support convection. Fire Weather is a concern, yet the precipitation during the weekend will lessen the threat. Yet, a weak disturbance moving through the area on Thursday does hint toward convection over the Sierra Nevada that day.

Monday/Tuesday will be a transition period as temperatures approach normal values and the region dries out. PoE will struggle to reach 95 degrees early in the week, but, will get more traction as a ridge builds back into the region later next week. PoE finally reaches percentages of 40% to 70% on Friday, with even high values on Saturday (60% to 80%) and increasing the confidence of reaching the mid 90s range.

AVIATION... 00Z Update:

VFR conditions will prevail for the next 24 hours across the Central California Interior. A slight chance (15%) of afternoon convection will exist across the Sierra Nevada until 03Z Sunday.

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... Heat Advisory until 7 AM PDT Sunday for CAZ300>321-324-332.