Hard to believe with the 80 degree temps and almost-cloudless sky today — but the National Weather Service says expect a big 'un tomorrow afternoon:

A BROAD UPPER LEVEL LOW PRESSURE SYSTEM IN THE EASTERN PACIFIC  WILL APPROACH THE WEST COAST THROUGH THURSDAY. RAIN IS EXPECTED TO PUSH INTO THE CENTRAL COAST EARLY THURSDAY MORNING…WITH RAIN REACHING LOS ANGELES COUNTY LATE THURSDAY MORNING OR THURSDAY  AFTERNOON. RAIN WILL TURN TO SHOWERS ON THE CENTRAL COAST THURSDAY  EVENING… BUT NOT UNTIL AFTER MIDNIGHT ACROSS LOS ANGELES COUNTY. AS COLDER AIR ALOFT WITH THE UPPER LOW PUSHES INTO THE REGION BEHIND THE SYSTEMS COLD FRONT…INCREASING INSTABILITY COULD CAUSE A THREAT OF THUNDERSTORMS THURSDAY AFTERNOON AND EVENING. RAINFALL FROM THIS FRONTAL SYSTEM IS GENERALLY EXPECTED TO RANGE FROM THREE QUARTERS OF AN INCH TO ONE AND ONE HALF INCHES IN COASTAL AND VALLEY AREAS...WITH ONE INCH TO ONE AND ONE HALF INCHES IN THE FOOTHILLS AND MOUNTAINS. THE SNOW LEVEL NEAR 7000 FEET EARLY THURSDAY MORNING WILL LOWER TO AROUND 6000 FEET BY THURSDAY AFTERNOON. WITH THESE TYPE OF SNOW LEVELS…SNOW ACCUMULATION IS NOT INITIALLY EXPECTED ACROSS  THE INTERSTATE 5 CORRIDOR. HOWEVER… ACCUMULATING SNOW IS POSSIBLE ABOVE 6000 FEET…AND WINTRY DRIVING CONDITIONS SHOULD BE EXPECTED IN HIGHER TERRAIN. THE NEXT IMPULSE ASSOCIATED WITH THE UPPER LEVEL TROUGH WILL APPROACH THE CALIFORNIA COAST ON FRIDAY. THERE IS EXPECTED TO BE A BREAK IN THE STEADY RAIN THURSDAY NIGHT…BUT ENOUGH LOW LEVEL MOISTURE IS PRESENT TO MAINTAIN SCATTERED SHOWER ACTIVITY. RAIN WILL LIKELY INCREASE IN COVERAGE AND INTENSITY ON FRIDAY THEN CONTINUE INTO FRIDAY NIGHT BEFORE TURNING TO SHOWERS AGAIN LATE.  DEPENDING UPON ITS TRACK… THE SECOND IMPULSE HAS THE POTENTIAL TO BRING HEAVIER PRECIPITATION THAN THE FIRST SYSTEM. ADDITIONAL  FLASH FLOODING AND DEBRIS FLOW CONCERNS WILL EXIST FOR THE RECENT BURN AREAS. THIS SECONDARY COLD UPPER LEVEL SYSTEM WILL LIKELY LINGER NEAR SOUTHERN CALIFORNIA THROUGH SATURDAY. DURING THIS TIME…LOWER SNOW LEVELS ARE EXPECTED…WITH SNOW POSSIBLY AFFECTING THE INTERSTATE 5 CORRIDOR NEAR THE GRAPEVINE. THE FINER DETAILS WITH THE SECOND IMPULSE STILL REMAIN SOMEWHAT UNCLEAR. HOWEVER…THERE IS A POTENTIAL FOR AN ADDITIONAL THREE QUARTERS OF AN INCH OF RAINFALL IN THE COASTAL AND VALLEY AREAS AND UP TO AN ADDITIONAL TWO TO TWO AND ONE HALF INCHES OF RAINFALL IN THE MORE FAVORABLE MOUNTAIN LOCATIONS. SOUTH FACING MOUNTAIN SLOPES ARE EXPECTED TO RECEIVE HIGHEST RAINFALL TOTALS FOR THE STORM SYSTEM. DUE TO THE COLD AND UNSTABLE NATURE OF THESE WEATHER SYSTEMS…THERE WILL ALSO BE THE POTENTIAL FOR WATERSPOUT ACTIVITY.