textproduct: San Joaquin Valley

KEY MESSAGES

1. Strong wind gusts and low relative humidities in the lower elevations of central California brings a Major Risk of Fire Danger through the remainder of the weekend.

2. Red Flag Warning in effect for the San Joaquin Valley and West Side Hills of the Coastal Range through Monday evening. Red Flag Warning in effect for the Mojave Desert through Sunday evening.

3. Strong wind gusts continuing in the Mojave Desert through Sunday, with a High Wind Warning for the Mojave Slopes and Wind Advisory for the remaining desert areas.

4. Lake Wind Advisory in effect for the Kern River Valley, Lake Isabella, and San Luis Reservoir.

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

DISCUSSION

An upper level trough is pushing through the western US this morning, with the center of the trough currently located over northern Nevada and central Idaho. Over the next few hours, the trough will move through Nevada, with the axis and a localized jet stream, moving over central California. Northwest flow assoicated with the jet streak will continue to bring cool, but dry conditions to the local area along with stronger wind gusts in lower elevations. The latter is due to the orientation of the prevailing flow channeling through the San Joaquin Valley as a result of the local terrain. This afternoon, there is a 60 to 70 percent probability for gusts to exceed 30 mph, especially in the western valley areas; low RH values between 15 and 20 percent across the same area will result in a major risk for fire danger in this area. In addition, strong wind gusts remain expected for the Kern County Desert (70 to 80 percent chance to exceed 50 mph) with the incoming jet streak, which will move over dry desert conditions, and continuing fire danger in this area.

For Monday, the leading edge of the trough will push eastward, but will become more longwave, with the trailing edge remaining relatively stationary over the western US. The result of this will be a continuation of dry air from the northwest, but with a with a slight warming trend due to the introduction of more zonal flow over central California. MinRH values at 15 to 20 percent on Sunday will quickly fall below 15 percent for much of the San Joaquin Valley and Kern County Mountains, and portions of the Sierra Nevada; minRH values in the Mojave Desert will fall below 10 percent. Lingering low level winds over the San Joaquin Valley will continue the threat for grass fires to develop and spread on Monday.

As the week progresses, upper level winds are expected to diminish as a slight high pressure ridge begins to build in. With upper level flow continuing from the north to northwest, regardless of the decrease in winds, dew point temperatures will remain mostly stable while air temperatures gradually increase. This will hold relative humidities at or below 15 percent across the lower elevations of central California for much of the week. Localized stronger wind gusts in the southern Sierra and Tehachapi Range will bring additional fire danger to these areas, especially where fuels have been curing the most over the past weeks.

AVIATION

VFR conditions will prevail for the next 24 hours. Gusts 25-30 kts will develop at the TAF sites again Sunday morning through the evening.

FIRE WEATHER

Low minRH values today combined with wind gusts approaching 30 to 35 mph in the San Joaquin Valley continues the threat for fast-moving grass fires; a Red Flag Warning remains in effect for this area until 8 PM Monday as minRH values under 15 percent are anticipated tomorrow. Red Flag Warnings also remain in effect for the Mojave Desert until 11 PM this evening due to minRH values at or less than 15 percent and strong wind gusts above 50 mph this afternoon. As stated above, drier air is expected to move into central California this week with minRH values at lower elevations expected less 15 percent for multiple days in a row.

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

Red Flag Warning until 11 PM PDT this evening for CAZ298-299. High Wind Warning until 11 PM PDT this evening for CAZ338. Wind Advisory until 11 PM PDT this evening for CAZ337-339. Red Flag Warning until 8 PM PDT Monday for CAZ579-580. Lake Wind Advisory until 8 AM PDT Monday for CAZ300. Lake Wind Advisory until 11 PM PDT this evening for CAZ332.