textproduct: San Joaquin Valley

UPDATE

Updated Aviation Section.

KEY MESSAGES

1. A storm will pass through central California late tonight through Wednesday this week and will bring valley rain, mountain snow and strong winds to the region.

2. Winter Weather Advisory in effect from 5 AM Tuesday through 5 AM Wednesday for the higher elevations in and around Yosemite NP.

3. Above average temperatures with dry conditions return Thursday through the weekend.

DISCUSSION

A low pressure trough is currently situated off the Pacific coast this evening, causing an influx of upper level cloud cover to cascade over central California. This trough is expected to push through the region in the coming days, with valley rainfall and mountain snowfall anticipated in the downstream from the axis Tuesday, and an increase in winds along the Sierra Crest and the Mojave Desert starting Wednesday after the trough passes through. In a 24 hour period ending 5 AM Wednesday, there is a 50 to 60 percent probability for rainfall greater than one-tenth of an inch for the San Joaquin Valley, with the greatest of these probabilities in the north and eastern portions of the valley; south valley areas including Avenal, Bakersfield, Coalinga, and Taft have only a 20 to 30 percent probability for these amounts. Over the Sierra Nevada, and especially the portion of the range north of Fresno County, there is an 80 to 90 percent probability for more than six inches of snow accumulation at the highest elevations over the same time frame listed above. This has led to the issuance of a Winter Weather Advisory for the back country of Yosemite National Park valid from 5 AM Tuesday through 5 AM Wednesday. Snow level projections remain between 7,000 and 8,000 feet.

As the trough passes through into Wednesday, stronger mid level winds will take hold from the Northwest, leading to strong expected gusts along the Sierra Crests and in the eastern slopes of the Tehachapi Range. For Wednesday, there is a 70 to 80 percent probability for maximum gusts to exceed 50 mph in these areas, which rises to 80 to 90 percent for Thursday. For Thursday, there is also a 50 to 60 percent probability for maximum gusts to exceed 65 mph along Walker Pass and along CA Route 58 just west of Mojave, CA.

Moisture will linger for the central Sierra into Thursday afternoon, but as the weekend approaches, ensemble cluster analysis shows good confidence in another high pressure ridge building over the western US. This will result in another warming trend with above-average temperatures for the region once again.

AVIATION

VFR conditions will prevail across central California across the next 24 hours. Strong winds developing over the Sierra Nevada Crest and across the Kern County Desert after 06Z Tuesday with surface winds gusting to 35 knots. 5 to 15 percent chance of thunderstorms after 18Z Tue for the Valley and Sierra Nevada.

FIRE WEATHER

A storm system moves in late tonight and continues for the next several days. RH values will improve with decreasing temperatures and ample moisture with the system. However, the system brings a slight chance (up to 10 percent) for thunderstorms to develop in the north and west San Joaquin Valley on Tuesday. Lightning from storms has potential to strike fuels that have been gradually curing through the recent warming trend. In addition, strong NW flow on the backside of the trough Friday into the weekend will introduce high winds and very low RH values, especially for the Kern Desert and southern Sierra Nevada where minRHs have potential to fall below 15 percent.

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

Winter Weather Advisory until 5 AM PDT Wednesday for CAZ323- 326.