textproduct: San Joaquin Valley

KEY MESSAGES

1. Lake Wind Advisory for San Luis Reservoir AND Lake Isabella through 11 PM PDT Thursday, July 7. Beware of unsettled waters.

2. Slow but steady warmup this week, with Heat Risk reaching elevated to major levels by weekend.

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

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

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

DISCUSSION

The Lake Wind Advisory for San Luis Reservoir has been extended to 11PM Thursday following model runs from this morning continuing to show high probability for gusts exceeding 25 MPH, especially in the late afternoon and early evening. High confidence also extends to the Kern River Valley, for which a Lake Wind Advisory for Lake Isabella has been issued, also until 11 PM Thursday.

Likewise, models continue to be in good agreement regarding the steady development of a high pressure ridge over our area, eventually evolving into a larger Omega block centered over the Four Corners and upper plains. As this develops, temperatures across our area will steadily increase. By Friday, there is high confidence for widespread triple digit heat across the San Joaquin Valley, Kern River Valley, and Mojave Desert. NBM further indicates a 40-50% probability for temperatures above 110 in the lower elevations of the Mojave Desert, including Ridgecrest and China Lake. Widespread, high probability for Moderate heat risk will continued to be monitored for a potential Heat Advisory product.

Concurrent with the warming trend will be a decrease in minimum relative humidities. Minimum relative humidity in the teens across most the region to mid single digits in the Mojave Desert are expected to coincide with the regional warmup. The combination of hot, dry, and diurnally windy conditions will create significant fire concerns, particularly in eastern Kern and Tulare Counties.

Looking further ahead, the establishment of an Omega block over the Four Corners will begin to redirect monsoonal moisture into our area. While this eastward shift of the high will help cool down the hot regional temperatures, this will also introduce an increased probability for thunderstorms across the Sierra Nevada and Mojave Slope. There is still large uncertainty regarding the probability of dry vs wetting thunderstorms, but a Red Flag Warning may be in order in the coming days if confidence for the former (dry lightning) increases.

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. 5-10% probability for gusty winds, brief heavy rain, and lightning in and near Sierra Crest thunderstorms.

FIRE WEATHER

The combination of hot temperatures, low relative humidity, and diurnal gusts will lead to increased fire risk region wide, with a particular focus on eastern Kern and Tulare County. Current Hot-Dry-Windy Index guidance places eastern Kern County above the 75th percentile Wednesday and onwards, significantly increasing the risk of fire starts. The monsoonal moisture push into our region late this weekend into next week will be closely monitored for the probability of dry lightning. If confidence continues to increase, a Red Flag Warning will follow, with the Mojave Slope and Sierra Nevadas the most likely regions affected.

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 Thursday for CAZ300. Lake Wind Advisory from 5 PM this afternoon to 11 PM PDT Thursday for CAZ332.