Heavy Snow in California, March 31, 2014

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
255 AM PDT MON MAR 31 2014

.DISCUSSION...A LARGE LOW PRESSURE SYSTEM CENTERED NEAR 43N 135W
WILL APPROACH THE COAST TODAY. RAIN IS ALREADY STARTING TO SHOW UP
ON RADAR OFFSHORE AND IT SHOULD BEGIN RAINING ALONG THE CURRY
COAST SHORTLY. THE SYSTEM LACKS A TROPICAL MOISTURE TAP, BUT
SATELLITE DATA SHOW RESPECTABLE PRECIPITABLE WATER VALUES WITHIN
THE PLUME WHICH ARE ON THE ORDER OF AN INCH OR SO. THIS IS THE
LEAST WE'D EXPECT TO SEE ON THE COAST AS THIS BAND MOVES ASHORE
AND MORE IN THE COASTAL MOUNTAINS DUE TO OROGRAPHIC EFFECTS. QPF
AMOUNTS WERE RAMPED UP OVER THE CURRY COAST AND ADJACENT MOUNTAINS
FOR TODAY. IN ADDITION, LOW PRESSURE AHEAD OF THE MAIN UPPER
TROUGH WILL BRING GUSTY WINDS TO THE REGION. WHILE GRADIENTS ARE
ACTUALLY NOT ALL THAT IMPRESSIVE (4-6 MB MFR-RDD, FOR EXAMPLE),
WINDS BECOME WELL ALIGNED FROM THE SURFACE THROUGH 850 MB THROUGH
THE SHASTA AND ROGUE VALLEYS. THIS SHOULD LEAD TO INCREASED WIND
SPEEDS IN THESE AREAS, AND WIND ADVISORIES ARE IN PLACE.

THE NEXT ISSUE IS SNOW ACROSS SISKIYOU COUNTY. ALL THE MODELS ARE
GENERALLY IN AGREEMENT THAT A SHOT OF MODERATE SNOW IS ON THE WAY
FOR MUCH OF SISKIYOU COUNTY ABOVE 3500 FEET, INCLUDING MOUNT
SHASTA CITY. SNOW WILL BEGIN IN THE WEST AFTER DAWN AND SPREAD
QUICKLY TO THE EAST. AS THE LOW SLIDES TOWARD THE NW CALIFORNIA
COAST THIS AFTERNOON, A STRONG AREA OF PVA ROTATES AROUND THE LOW
AND ACROSS THE SISKIYOU COUNTY. THIS WILL PRODUCE A PERIOD OF
ENHANCED PRECIPITATION, ESPECIALLY THROUGH THE CENTRAL PART OF THE
COUNTY, AS WELL ALIGNED SOUTHERLY FLOW AND UPPER LEVEL ENHANCEMENT
MAKE THE MOST OUT OF THE AVAILABLE MOISTURE. THINK THE PERIOD OF
LATE AFTERNOON THROUGH EARLY EVENING IS WHEN THE I-5 CORRIDOR
THROUGH MT. SHASTA HAS THE GREATEST POTENTIAL FOR IMPACTS FROM
SNOW AS ROAD SURFACES COOL AND SNOW RATES PEAK. THIS IS ALL
COVERED IN THE CURRENT WINTER STORM WARNING, AND ALL I DID WAS
EXPAND THIS WARNING A LITTLE FURTHER EAST INTO SOUTHEAST SISKIYOU
COUNTY.

AS THIS SHORTWAVE SWINGS NORTH INTO OREGON MID TO LATE EVENING,
SNOW WILL DECREASE QUICKLY FROM WEST TO EAST ACROSS CALIFORNIA. I
MOVED UP THE END TIME OF THE WINTER STORM WARNING FOR WESTERN
SISKIYOU TO 11 PM AS ALL MODELS SHOW SNOW DIMINISHING QUICKLY
THERE. AS THIS WAVE PIVOTS ACROSS OREGON LATE THIS EVENING, WE
WILL SEE SNOW PICK UP ACROSS KLAMATH AND LAKE COUNTIES. WE ARE
CURRENTLY ONLY EXPECTING A FEW INCHES ACROSS THE REGION TONIGHT,
SO HEADLINES ARE NOT WARRANTED. BUT TRAVELERS THROUGH THE AREA
OUGHT TO TAKE NOTICE AS IT WILL COME AT NIGHT AND WILL STICK TO
THE ROADS. MODOC COUNTY WILL ALSO SEE SOME ACCUMULATING SNOW
OVERNIGHT, AND WHILE AMOUNTS SHOULD BE LIGHT, IT WILL ALSO STICK
TO THE ROADS THERE.

THE LOW DROPS FURTHER SOUTH INTO CALIFORNIA ON WEDNESDAY WHICH MAY
LEAD TO A DRY DAY FOR MUCH OF THE REGION. A WEAK FRONT WILL MOVE
THROUGH THURSDAY INTO FRIDAY WITH MORE PRECIPITATION POSSIBLE.
UPPER RIDGING STARTS TO DEVELOP FRIDAY AND BEGINS TO SHUNT
PRECIPITATION NORTH OF US. MODEL CONSENSUS SHOWS THIS RIDGE
BUILDING STRONGLY OVER THE PACNW SUNDAY INTO EARLY NEXT WEEK FOR
DRIER AND WARMER WEATHER. -WRIGHT

&&

.AVIATION...BASED ON THE 31/12Z TAF CYCLE...CONDITIONS WILL BE
MAINLY VFR THIS MORNING AS A COLD FRONT APPROACHES THE COAST AND
RAIN PUSHES INLAND.  ISOLATED MVFR CIGS AND MOUNTAIN OBSCURATIONS
WILL BECOME MORE WIDESPREAD WITH TIME...GENERALLY PROGRESSING FROM
WEST TO EAST OVER OREGON. ADDITIONALLY...LOW LEVEL WIND SHEAR IS
EXPECTED AT THE COAST THIS MORNING AHEAD OF THE COLD FRONT. THE
HEAVIEST PRECIPITATION AND WIDESPREAD MOUNTAIN OBSCURATION WILL BE
OVER NORTHERN CALIFORNIA NEAR SOUTH FACING SLOPES AND ALONG AND JUST
EAST OF THE CASCADES MONDAY AFTERNOON THROUGH THE EVENING...WITH
HEAVY SNOW LIKELY OVER PARTS OF NORTHERN CALIFORNIA THIS AFTERNOON
THROUGH THE OVERNIGHT HOURS.

&&

.MARINE...WINDS ARE ALREADY INCREASING OVER THE WATERS AS A COLD
FRONT APPROACHES. THE NAM SHOWS A COASTAL JET DEVELOPING OVER THE
OUTER AND OUTER PORTIONS OF THE INNER WATERS WITH GALE FORCE WINDS
AND STEEP WIND DRIVEN SEAS LIKELY TO DEVELOP EARLY THIS MORNING.
THE STRONGEST WINDS ARE EXPECTED TO BE BETWEEN NOW AND 18Z, THEN
WILL WEAKEN THIS AFTERNOON. LOW PRESSURE WILL MOVE SOUTH JUST WEST
OF THE OUTER WATERS TONIGHT...THEN MOVE SOUTHWEST OFF THE CALIFORNIA
COAST TUESDAY. THE MODELS SUGGEST WINDS COULD REACH SMALL CRAFT FOR
A SIX HOUR PERIOD TUESDAY MORNING, BUT WE'LL HOLD OFF ON HEADLINING
THIS UNTIL THE CURRENT HEADLINE EXPIRES. WINDS AND SEAS WILL SETTLE
DOWN AS WEAK HIGH PRESSURE BUILDS OVERHEAD WEDNESDAY. THE GFS AND EC
DIFFER ON THE TIMING OF THE NEXT FRONT. THE EC IS FASTER WHILE THE
GFS IS SLOWER. IN ANY CASE THE FRONT IS WEAK AND SHOULD HAVE MINIMAL
IMPACT OVER THE WATERS. -PETRUCELLI

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...WIND ADVISORY FROM 10 AM THIS MORNING TO 9 PM PDT THIS EVENING
     FOR ORZ026.

CA...WIND ADVISORY FROM 10 AM THIS MORNING TO 9 PM PDT THIS EVENING
     FOR CAZ081.
     WINTER STORM WARNING FROM 2 PM THIS AFTERNOON TO 11 PM PDT
     THIS EVENING ABOVE 3500 FEET FOR FOR CAZ080.
     WINTER STORM WARNING FROM 2 PM THIS AFTERNOON TO 5 AM PDT
     TUESDAY ABOVE 3500 FEET FOR FOR CAZ082-083.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS UNTIL 2 PM PDT
     THIS AFTERNOON FOR PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 2 PM PDT THIS
     AFTERNOON FOR PZZ350-356-370-376.
     GALE WARNING UNTIL 2 PM PDT THIS AFTERNOON FOR
     PZZ350-356-370-376.
     HAZARDOUS SEAS WARNING UNTIL 2 PM PDT THIS AFTERNOON FOR
     PZZ350-356-370-376.