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

Lake Wind Advisory for San Luis Reservoir and Lake Isabella through 11 PM PDT Friday, July 10. Sustained winds 15 to 20 mph and gusts as high as 35 mph will create hazardous conditions for small craft and high-profile vehicles.

Zonal flow prevails at the moment as a high pressure sits just west of the Four Corners region, bringing the area dry and warm conditions, with high temperatures a bit above normal. The high pressure will continue to retrograde westward over the next day or two, bringing further increased temperatures. High temperatures in the Valley today will be in the upper 90s and low 100 and near 100 to 105 tomorrow. Desert highs will be 105-115 today, holding at similar values tomorrow.

As the high moves westward, winds will increase in the desert. Maximum wind gusts will be 20-25 mph in the Valley today and 15-20 mph Thursday. In eastern Kern and Tulare Counties, maximum wind gusts will be 40-55 mph today, decreasing to 35-45 mph tomorrow. These winds will be hazardous to drivers in the area, particularly those in high-profile vehicles.

Relative humidity will also decrease as the high moves westward. Minimum relative humidities will be 12-20% in the Valley today and tomorrow. In the desert, minimum relative humidities will be 6-10% today, decreasing to 4-8% tomorrow.

The distinct combination of above-average temperatures, windy conditions, and dry air will create concerning fire conditions in eastern Kern and Tulare Counties Thursday and Friday.

As we move into the weekend, the high will migrate northeastward. This will alter overall flow to a southeasterly direction, bringing a surge of monsoon moisture to the region. As this happens, lightning chances will increase along the Sierra Crest and into the desert, with a 5-10% probability of lightning Sunday, increasing to 10-30% on Monday and continuing similarly for several days. Despite the surge of moisture, there will also be a dry lightning risk associated with some storms.

As the heat continues, be sure to take appropriate precautions and check in on and make arrangements for vulnerable people and animals. Brachycephalic (short-nose) breeds will have particular difficulties with the heat and should be kept indoors.

If driving or boating in an area with a Wind Advisory, take appropriate precautions.

Water temperatures are still in the upper 60s and low 70s and much colder near water flowing from higher elevations. Exercise cold water safety at all times.

AVIATION

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

FIRE WEATHER

Rising temperatures into this weekend will create drier conditions across the region, with minimum relative humidity values at 12 to 20 percent across the San Joaquin Valley and between 5 and 10 percent for the Sierra Nevada and Kern County Desert Thursday. A gradual improvement will occur over the following days, but largely remain within 5 percent of Thursday's minimums. Stronger wind gusts approaching 40 mph in the Mojave Desert Slopes will cause elevated fire weather conditions when combined with the low RH values. In the late weekend, an influx of monsoonal moisture will bring showers and thunderstorms to the Sierra Nevada, with chances currently sitting at 20 to 30 percent each day beginning late Sunday. Outside of the mountain areas, temperatures will remain above 100 degrees as flow tracks into the region from the southeast.

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.