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

Lingering monsoonal moisture is expected to continue to lead to afternoon thunderstorm chances of 15-25% once again over the Sierra Nevada crest tomorrow afternoon, though these chances are currently not as strong as the values seen this afternoon. Due to these chances, the Storm Prediction Center has places the Sierra Nevada under a general risk for thunderstorms, but the Weather Prediction Center has shifted the risk for excessive rainfall eastwards, as the probability for that heavy precipitation is more likely to the leeward side of the mountains. That said, the thunderstorms that do form may still produce localized heavy rainfall, as well as small hail and lightning.

As seen this afternoon, the cloud cover that was present the last few days cleared out and high temperatures were able to rise several degrees into the mid 100's, which is expected to reoccur tomorrow as the ridge remains strong over the region. However, at the same time, a trough off the coast of Oregon and Washington will cause a tighter pressure gradient over Northern and Central California. This will then cause slightly strong winds over the San Luis Reservoir and the Mojave Desert Slopes. This air will also be drier than the monsoonal air that had been coming up from the south, leading to an elevated fire risk for much of the Valley and West Side Hills tomorrow and especially Thursday. Thursday is also the day highs will begin to see a cooling trend and by Monday of next week, temperatures in most of the Valley are expected to be in the low to mid 90's, which is a couple degrees below normal for this time of year.

Looking to the long term, a warm-up continues to show up in the model runs, with the Climate Prediction Center placing our CWA into the leaning above normal category for both the 6 to 10 and 8 to 14 day outlooks. The San Joaquin Valley is also highlighted in the hazard outlook with a slight risk (20-40%) for extreme heat from the 22nd through the 28th of July.

AVIATION

Thunderstorms may lead to mountain-obscuring clouds after 21Z Wed through 03Z Thu. 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.