Marine Weather and Tide Forecast for Atwater, CA

KEY MESSAGES

1. Winter Storm Warning in effect for the Sierra Nevada above 7,000 ft.

2. An approaching cut-off low brings periods of heavy rainfall and mountain snow by early Tuesday, with favorable conditions for convective weather afterwards.

DISCUSSION
A large band of stratiform rain has been moving into Northern California from the southwest for the past few hours, and it will soon shift course and move over our CWA, likely by midnight tonight. Precipitation in the foothills and upper Sierra Nevada can be expected to start around 5am and the rest of our CWA will start to see rainfall by 11am tomorrow morning. Widespread rainfall is expected through at least 5pm for the Sierra Nevada and its foothills. Current probabilities for an inch of rainfall in the Foothills north of Kings Canyon are 60-80% for the 24 hour period ending Tuesday at 11pm. There is also a Marginal Risk (at least 5%) for excessive rainfall in that area, along with the San Joaquin Valley from Visalia to Los Banos as the crow flies.

For the Sierra Nevada, heavy snow is expected above 7000 feet, with totals of 3 to 5 inches above that elevation and 12 to 18 inches at the highest elevations, mainly around Yosemite NP. Due to this, a Winter Storm Warning has been issued for the Sierra Nevada mountains from Sequoia NP northwards from 2am Tuesday morning through 5pm Wednesday afternoon. Along with this heavy snow, strong wind gusts of 75 mph or higher are also expected with this system, and not just for the Sierra Nevada. There is a 40-60% chance of 64 mph gusts or higher along the Mojave Desert Slopes and similar chances for 55 mph gusts in the Mojave Desert itself on Tuesday as well. A Wind Advisory has been issued for both of these regions, the advisory on the slopes lasting until 8pm tomorrow night, and the advisory on the desert expiring earlier at 7am on Tuesday.

As the main rain band moves through the region Tuesday afternoon, the chances for thunderstorms increases into the 30 to 45% range in the Valley from Porterville north. The southern half of the Valley can expect a 15-30% chance of thunderstorms.
This is due to the increased dynamics behind the initial wave combined with the newly fallen moisture and afternoon heating.
As of today, the Storm Prediction Center has put this area under a general risk for thunderstorms. Severe thunderstorms are not expected. However, any cell that forms still comes with the risk for small hail, frequent lightning, gusty winds, and localized flooding.

After this system moves east and the precipitation moves on, a weak trough may still hang around aloft, with current ensemble models continuing to agree with that forecast. A second, albeit weaker, cut-off low may develop later this week and produce some precipitation by the weekend, particularly in the Sierra Nevada. This weak trough will also keep temperatures around normal through the weekend.


AVIATION
MVFR with Local IFR over the Higher Terrain of the Sierra Nevada.
Otherwise, VFR conditions expected across the area for the next 24 hours, with Valley and Foothill MVFR conditions in and around thunderstorms from about 18Z Tuesday through 06Z Wednesday.

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 2 PM Tuesday to 8 PM PDT Wednesday for CAZ338.

Winter Storm Warning from 2 AM Tuesday to 5 PM PDT Wednesday for CAZ323-326>328-330.

Wind Advisory from 2 PM Tuesday to 7 AM PDT Wednesday for CAZ337-339.