Area Forecast Discussion

KEY MESSAGES

1. Warming and drying trend continuing tomorrow with temperatures rising to above average.

2. An elevated risk for fire starts in Kern County due to low humidity and increased winds, particularly across the Mojave Desert.

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

DISCUSSION

Current satellite imagery shows the storm system that will impact Central California this week just off the coast of the western CONUS. Before this system arrives, however, above normal temperatures are still expected tomorrow afternoon, due to the shortwave ridge that still holds its influence aloft. Highs will see a downtrend of a few degrees, but will remain around 7 to 10 degree above normal.

Looking to the more active weather, the cut-off trough is expected to begin Monday evening and continue through Wednesday afternoon. The majority of the precipitation is expected Tuesday morning through the afternoon as a large rain band moves through the region during that time period, and the most impacted areas are expected to be 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 possible 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 Watch 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.

As the main rain band moves through the region Tuesday afternoon, the chances for thunderstorms increases into the 25 to 35% range for the north Valley and the foothills, mainly behind that band. 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 and severe thunderstorms are not expected. However, any cell that forms still comes with the risk for small hail, frequent lightning 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. This trough would keep temperatures around normal through the rest of the week before it begins to move east and become another cut- off low, though much weaker than the upcoming system. This second cut-off may still produce some precipitation by next Sunday, though much lighter in comparison and confined to the Sierra Nevada. The Climate Prediction Center also continues to support this outcome as the 6-10 day outlook has Central California under likely above average precipitation. The 8-14 day outlook does drop into the leaning above normal precip category, suggesting a lowered likelihood for precip next week.

AVIATION

VFR conditions expected across the area for the next 24 hours.

FIRE WEATHER

Above normal temperatures are expected to continue for the region through Monday afternoon. Humidity will continue to be very dry across the region as a result. Elevated fire risk is expected particularly for the Mojave Desert with a decrease in minRH values between five and ten percent. Wind gusts will increase for the Mojave Slopes during the afternoons. An approaching system brings a pattern change late Monday, with precipitation across much of the region anticipated from then until Wednesday afternoon.

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 Storm Watch from late Monday night through Wednesday afternoon for CAZ323-326>328-330.