textproduct: San Joaquin Valley

KEY MESSAGES

1. Moderate to Major Heat Risk on Tuesday and Wednesday.

2. Elevated (>25%) probability of thunderstorms along the Sierra Nevada remains through Wednesday.

3. Slow moving mountain thunderstorms can produce excessive rainfall.

4. 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 Wednesday and Thursday.

DISCUSSION

Heat Dome high pressure pushed back toward the West Coast as Central California starts another heat wave. Probability of Exceedance (PoE) of reaching 105 degrees ranges from 40 to 65 percent Today and Wednesday as hot and humid conditions will place the valley floor in the Major Heat Risk category. Heat Advisory is in place as dangerous conditions will exist through at least Thursday. A change in the flow will push the heat east, along with the humidity, as the area slowly dries out. With PoE of reaching 100 degrees dropping to 50 percent or less by Saturday, will see less of a Heat Risk on Friday and Saturday before another warm-up around the middle of next week.

High pressure center near the Four Corners area will continue to allow for additional monsoonal type moisture to surge north and toward Central California. Doppler radar is showing showers to the east of Central California and steering mostly northward. Yet, with high precip-water values still over the region and surface dew points in the mid 50s to near 60 degrees, the area still has plenty of moisture to initiate good afternoon convection. Excessive rainfall will still be a problem as ensemble precipitation analysis still has a 30-40 percent chance of reaching a tenth of an inch (0.10) over the Sierra Nevada Crest today. In addition,there is also a 20 to 50 percent probability for thunderstorms across the Sierra Crest Today. While probabilities do drop off later in the week, thunderstorms can not be ruled out until at least Saturday.

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 50-60 percent chance that temperatures will likely be above normal conditions.

AVIATION

Thunderstorms may lead to mountain-obscuring clouds after 21Z Tue through 03Z Wed. Otherwise, VFR is expected across the central California interior 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.