textproduct: San Joaquin Valley

KEY MESSAGES

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

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

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

DISCUSSION

A strong warmup is well on its way for central California as a ridge of high pressure gradually builds in through the weekend and into early next week. On Friday, there is a 70 to 80 percent probability for afternoon highs to exceed 90 degrees in the southern San Joaquin Valley, with similar probabilities on Saturday. These probabilities increase to 80 to 90 percent on Sunday for the entire San Joaquin Valley before rising further to 90 to 100 percent for Monday and Tuesday.

The ridge of high pressure is expected to slowly move over the Four Corners region Monday and Tuesday, bringing weak south to southeast flow over central California, becoming the main driver for these warmer temperatures. On Monday, there is a 70 to 80 percent probability for temepratures to exceed 100 degrees in the west and south valley areas, then expanding to include the majority of the San Joaquin Valley.

Weak amounts of moisture moving north across the Sierra Nevada will result in a 10 to 15 percent chance for thunderstorms along the crests starting Tuesday afternoon. Should conditions stay dry at higher elevations, there is a risk for dry lightning in any storms that may develop along with typical thunderstorm risks including small hail and gusty and erratic winds.

A slight cooling trend will set up starting next Wednesday as the aforementioned ridge progresses eastward. However, afternoon highs through at least Thursday will remain around ten degrees warmer than 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 Friday, 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 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. Additionally, subsidence from the high pressure ridge will keep winds relatively light across the region.

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

None.