textproduct: San Joaquin Valley

KEY MESSAGES

1. Warming trend through the end of the week. Cooling possible early next week.

2. Winds become gusty and from the east over the Sierra Crest and eastern Kern County Thursday into the weekend.

3. Along with dry conditions as Relative Humidity remains low, a Fire Weather Watch has been posted for the Kern County Mountains from Thursday through Friday.

4. A change in the weather will be in store early next week as a disturbance crosses the West and introduces unsettled conditions.

DISCUSSION

While the cooler temperatures the last few days were a welcome sight, they will unfortunately be fairly short-lived due to low pressure system that has brought these conditions pushing eastward into the Great Plains. However, a cut off area of low pressure is anticipated to break from this shortwave trough by Thursday, setting up over southern California. Meanwhile, an area of high pressure will build over northern California, extending into Nevada, Oregon, and Idaho. This pattern is known as a "Rex Block", where the prevailing westerly flow splits to the north around the high and to the south around the low, resulting in mostly stagnant conditions located in the block. Because of this new pattern, temepratures will gradually warm across central California, nearing ten degrees above season averages again this weekend. For the San Joaquin Valley, there is a 60 to 70 percent probability for afternoon highs to exceed 90 degrees for both Friday and Saturday, resulting in widespread Minor HeatRisk with pockets of Moderate HeatRisk. The lack of greater HeatRisk levels is thanks to cooler overnight temperatures compared to the previous heat wave earlier this month.

While the blocking pattern directs the large-scale atmospheric flow around the local area, a smaller-scale influence will develop from this pattern in the shape of increased winds between the conflicting pressure systems from the northeast. The direction of the incoming winds will bring in much drier air in addition to the increasing temperatures. Relative humidity values will be rather summer-like across the region, with minimums largely between 15 and 20 percent beginning Wednesday and lasting through the weekend except for at the highest elevations. The stronger pressure gradient between the aforementioned high and low results in moderate probabilities (40-50%) for maximum wind gusts to exceed 35 mph over the Sierra Crest and Kern County Mountains. There are also high probabilities (70-80%) for maximum gusts to exceed 45 mph in the Mojave Desert Slopes.

Into next week, ensemble cluster analysis shows agreement in a low pressure system passing through central California after dropping in from the north Pacific, with potential to bring precipitation to the region. As of now, there is a 20 to 30 percent probability for measurable rainfall (greater than 0.01") over 24 hours ending Wednesday morning in the San Joaquin Valley, and greater probabilities with increasing altitude. Lowered snow levels associated with this colder system has moderate probabilities for the peaks to receive a trace or more of snowfall.

AVIATION

VFR conditions will prevail for the next 24 hours.

FIRE WEATHER

Stronger wind gusts developing Thursday and Friday across the higher elevations of Kern County paired with minimum relative humidities approaching 15 to 20 percent will bring an increased risk for fire danger. Overnight recoveries reaching 40 percent at best will extend the threat into the overnight hours as well. Due to this, a Fire Weather Watch has been issued for the time period, focused on the areas from Frazier Park and Pine Mountain Club to the areas between Lake Isabella and Tehachapi.

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

Fire Weather Watch from Thursday morning through Friday evening for CAZ596-597.