textproduct: San Joaquin Valley

KEY MESSAGES

1. Lake Wind Advisory for San Luis Reservoir and Lake Isabella through 11 PM PDT Friday, July 10. Beware of unsettled waters.

2. Slow but steady warmup this week, with widespread Moderate Heat Risk by the weekend and isolated areas of Major Heat Risk.

3. Hot, dry, and windy conditions will create elevated fire risk today and tomorrow, particularly in eastern Kern and Tulare Counties.

4. Increased chance for Sierra Nevada thunderstorms late this weekend into next week with monsoonal moisture pushing into our region.

5. Practice safety around lakes, rivers, and streams, as water is still running cold.

DISCUSSION

High pressure has set up over southern and central California today which resulted in warmer temperatures across the region compared to earlier in the week. Many locations of the San Joaquin Valley approached the upper 90s with a handful of locations reaching triple-digits. As the high continues to build, probabilities for 100 degrees in the valley areas rise to 70 to 80 percent Friday and Saturday. For the remainder of the region, temperatures will be around five degrees above season averages going into the weekend.

Gusty conditions will remain across portions of central California, especially for the areas in the lee of mountain ranges and the typical wind prone areas including San Luis Reservoir, Lake Isabella, and the Mojave Desert Slopes. Lake Wind Advisories have been extended for the lake areas listed until 11 PM Friday. West winds 15 to 20 mph with gusts up to 35 mph are expected for San Luis Reservoir and west winds 15 to 25 mph with gusts to 35 mph for Lake Isabella.

Drier conditions remain expected alongside the triple- digit heat, with minimum relative humidity between 15 and 20 percent for the San Joaquin Valley, and between 5 and 15 percent for the higher elevations of the Sierra Nevada and single-digits in the Kern County Desert. These low humidity values will slowly improve through the next few days before a dramatic increase due to monsoonal moisture pushing into the region from the southeast.

Between Sunday and Monday, the aforementioned high pressure system remains favorable to push eastward over the Great Basin, prompting the upper level flow to shift to the southeast. This will bring warm, saturated air to the region, maintaining temperatures in the low 100s for the lower elevations, but resulting in chances for showers and thunderstorms over the Sierra Nevada. Ensemble guidance from the National Blend of Models has risen to a 60 to 70 percent probability for at least one- tenth of an inch over 24 hours ending 5 AM Tuesday for the Sierra between Fresno and Tulare Counties. There is also a 20 to 30 percent probability for thunderstorms across this area each day Monday through at least Thursday as there is little deviation in the synoptic pattern through the middle of next week.

The continued heat into next week will bring widespread Moderate HeatRisk and growing areas of Major HeatRisk in the San Joaquin Valley by Wednesday. This is largely due not just to the rising afternoon highs, but also warming morning lows. Ensemble guidance expresses a 70 to 80 percent probability for morning lows to exceed 70 degrees during the morning hours Tuesday through Thursday; the greatest of these probabilities are in the southern San Joaquin Valley, Kern County Desert, and the Foothills of the Sierra Nevada and Coastal Range where the thermal belt will reside.

AVIATION

VFR conditions expected across the area for the next 24 hours.

FIRE WEATHER

Rising temperatures into this weekend will continue drier conditions across the region. A gradual improvement in relative humidity will occur over the next few days, but largely remain between 15 and 20 percent for the San Joaquin Valley, and between 10 and 15 percent for the Sierra Nevada, and in single digits for the Kern Desert. Winds will be approaching 25 to 30 kts for the Lake Isabella area and the Mojave Slopes, resulting in elevated fire weather conditions. In the late weekend, an influx of monsoonal moisture will bring showers and thunderstorms to the Sierra Nevada, with chances sitting at 20 to 30 percent each day beginning Monday. Outside of the mountain areas, temperatures will remain above 100 degrees.

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

Lake Wind Advisory until 11 PM PDT Friday for CAZ300-332.