textproduct: San Joaquin Valley

KEY MESSAGES

1. Red Flag Warning issued for the Sierra Nevada above 4000 feet due to high winds and low relative humidity from Thursday morning through Friday evening.

2. A warming trend continues through the weekend before a cooldown next week.

3. Wind Advisory has been issued for the Mojave Desert zones from Thursday AM through Friday night with wind gusting up to 55mph.

4. A pattern change may be upon us early next week as a disturbance crosses the West and introduces unsettled conditions.

DISCUSSION

Temperatures across Central California this afternoon reflected the projected warming trend for this week, rising four to five degrees from yesterday. The anticipated pattern shift will gradually appear now through Thursday afternoon in which a localized area of low pressure will cut off from a shortwave trough that is currently making its way through the Great Basin region. While this cutoff low slides into southern and Baja California, a high pressure ridge will build in over northern California, Nevada, Oregon and Idaho. The large-scale atmospheric flow will subsequently split: tracking to the north around the high and to the south around the low. Stagnant conditions will develop over California initially, but the strengthening pressure gradient between these two conflicting systems will cause winds to increase from the east in the lower levels of the atmosphere. Warm, dry air from Nevada will rise over the eastern Sierra Nevada before descending into the foothills and Central Valley, further raising temperatures through the weekend. For the San Joaquin Valley, there is an 80 to 90 percent probability for afternoon highs to exceed 85 degrees on Thursday and Friday, with an additional 50 to 70 percent probability to exceed 90 degrees on Friday. These maximum temperatures will once again approach ten degrees above season averages.

As mentioned above, winds will increase over the eastern portions of Central California due to the upcoming pattern, particularly for the Sierra Nevada and Kern County Mountains and Desert. For the Sierra Nevada crests, there is a 50 to 60 percent probability for maximum gusts to exceed 35 mph both Thursday and Friday, though likely during the overnight hours leading to similar probabilities on both days. However, winds will not only be stronger for Kern County, but also last further into Friday. There is a 70 to 80 percent probability for maximum gusts to exceed 40 mph in the Lake Isabella area on Friday, with similar probabilities for 50 mph gusts in the Mojave Desert Slopes, including the town of Mojave, Walker Pass, and California Routes 14, 58, and 178. Due to these stronger winds, a Wind Advisory has been issued for the desert portion of Kern County valid from 6 AM Thursday through 10 PM Friday.

This hot, dry pattern will lose its hold over the region towards the latter part of the weekend. The weakening block will allow a more dynamic low pressure trough to push into the western US early next week, bringing the best chances for widespread precipitation for central California since April. Ensemble guidance from the NBM expresses a 40 to 50 percent probability for at least measureable rainfall (greater than 0.01") in the San Joaquin Valley next Wednesday, and 20 to 30 percent for a wetting rainfall (greater than one-tenth of an inch). Probabilities increase with elevation, with moderate probabilities (50 to 60 percent) for at least a trace of snowfall above 8000 feet.

AVIATION

VFR conditions will prevail for the next 24 hours.

FIRE WEATHER

Increased winds across the crests of the Sierra Nevada and the Kern County Mountains and Desert will transport warm, dry air from Nevada, lowering minimum relative humidities between 15 and 20 percent for much of central California for Thursday and Friday. Overnight recoveries will be poor between these two days, especially for the Sierra Foothills and Mojave Desert, where values are expected only between 20 and 30 percent. When combined with the expected strong wind gusts, these low RHs will allow any new fire development to spread rapidly and prolong the burning period well into the overnight hours. As such, a Red Flag Warning has been issued for the entire Sierra Nevada above 4000 feet along with the Kern County Mountains.

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

Wind Advisory from 6 AM Thursday to 10 PM PDT Friday for CAZ337>339. Red Flag Warning from 3 AM Thursday to 10 PM PDT Friday for CAZ592>597.