textproduct: San Joaquin Valley

KEY MESSAGES

1. Moderate Heat Risk on Thursday.

2. Elevated Fire Weather Concerns across portions of the San Joaquin Valley and West Hills of the Coastal Range for increased winds and low humidity on Thursday.

3. Seasonally average weather returns this weekend. Next warm-up expected later next week.

DISCUSSION

With the strongest high pressure ridging moving eastward, area- wide temperatures Thursday will not be as hot as Wednesday. Once the day is over, the current Heat Advisory will be reevaluated and adjusted as necessary. Latest probabilistic heat guidance indicates a notable decrease from Wednesday's extensive, very high confidence for regional Moderate Heat Risk. By the weekend, near normal temperatures return as the pattern overhead shifts to more neutral flow. In the longer term, confidence for triple digit heat does not increase until the later part of next week.

Meanwhile, a closed low off the Oregon coast is just close enough to promote breezy, downslope winds off the Coastal Range into the San Joaquin Valley. Combined with our return to low regional humidity and hot weather, another day of elevated fire weather concerns will continue for the San Joaquin Valley and western foothills along the Coastal Range. By Friday, the closed low promoting this flow pattern will shift further northward into British Columbia, decreasing sustained wind speeds and lowering the fire weather concern.

With the departure of our monsoon moisture push from the start of this week, thunderstorms will return to the typical, late afternoon chances for the Sierra Crest. Current guidance indicates a slight (<10%) probability for thunderstorms across the crest through the rest of the work week. Furthermore, without the abundant mid and upper level moisture observed in days past, any thunderstorms that do form are not favorable for severe weather impacts such as heavy rainfall and large hail.

Longer range ensemble analysis has the heat dome centered closer to the Mid-West as the associated flow pattern pushes the monsoon moisture back toward Central California late in the weekend. Climate Prediction Center (CPC) is indicating that the extended time frame of the 6 to 10 day period will remain on the warm side. Current CPC analysis has a 40-50 percent chance that temperatures will lean toward above normal conditions.

AVIATION

VFR conditions expected 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

Heat Advisory until 11 PM PDT Thursday for CAZ301>303-305>307- 309>317-319-321.