textproduct: San Joaquin Valley

KEY MESSAGES

1. Heat Advisory issued for the San Joaquin Valley and for Lake Isabella valid from 11 AM Monday, May 11th through 8 PM Tuesday, May 12th.

2. Early season heat arrives early next week with expected temperatures rising to triple-digit values Monday and Tuesday in the San Joaquin Valley.

3. Moderate Heat Risk expected for the valley areas, with a medium chance for Major Heat Risk.

4. Practice safety around area lakes, rivers, and streams as waters are running cold.

DISCUSSION

Dry conditions with a gradual warming trend are expected through the weekend and early next week as a high pressure ridge builds in over California. Temperatures will reach into the lower 90s on Saturday across the San Joaquin Valley and Mojave Desert, around 10 degrees above season normals before rising further into the mid 90s on Sunday. Monday and Tuesday are favorable to be the peak of the heating episode, with a 60 to 70 percent probability for temperatures to exceed 100 degrees on Monday valley-wide, but with a slightly smaller area or these chances on Tuesday. Nevertheless, a Heat Advisory has been issued for both days across the San Joaquin Valley, along with the Lake Isabella area, due to expected temperatures up to 102 degrees along with Moderate HeatRisk present. A drying trend will accompany the rising temperatures, with minimum RHs in the valley areas projected to be less than 15 percent on Monday, raising the risk for grass fires. Winds will largely be light and diurnal through the forecast period, however as the ridge slowly progresses eastward on Tuesday, anticyclonic flow around the center axis will result in stronger wind gusts from the southeast for the eastern side of the southern Sierra.

While the ridge progresses eastward, a low pressure trough is projected to push into the Pacific coastal states. A slight push of moisture into southern California ahead of the trough will bring a 10 to 15 percent chance for thunderstorms along the Sierra Nevada crest as the air moves over the warmer valley temperatures and moves up the terrain. Stronger wind gusts will accompany the trough as it moves through midweek, especially along the Sierra Crest and in the Mojave Slopes. The increased dynamics of the low will also bring some relief from the early week heat, dropping valley highs into the mid 80s, but remaining above season averages.

AVIATION

VFR conditions will prevail for the next 24 hours over Central California.

FIRE WEATHER

Warming temperatures through this weekend and early next week will result in lowering relative humidities across the region. Beginning today, minimum RHs in the Mojave desert will fall below 20 percent, and below 15 percent on Saturday. For Sunday through Tuesday, minRHs are expected between 5 and 10 percent in this area. RHs will fall to or below 20 percent in the San Joaquin Valley and Sierra Nevada Friday afternoon and continue at these values into the weekend. RHs at 15 percent or less are expected for these areas on Monday and Tuesday, with the Tehachapi Range and southern Kern Mountains at or below 10 percent. A downtrend in 100- and 1000-hr dead fuel moistures is anticipated with this warming trend, however both parameters are expected to remain above critical thresholds. Upsloping winds from the southeast along the eastern Sierra can help to further dry fuels, especially in the portion of the range in southern Tulare County. New fire starts may also spread more quickly with increased gusts along the southern Sierra.

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 from 11 AM Monday to 8 PM PDT Tuesday for CAZ300>317-319-321-332.