Debris Flows and Flooding in California, April 3 to 5, 2006

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HANFORD CA
315 AM PDT MON APR 3 2006

.SHORT TERM...FOR THE CENTRAL CALIFORNIA INTERIOR...RADAR SHOWS ONE
BAND OF RAIN AND HIGHER ELEVATION SNOW NOW AFFECTING THE EASTERN
AND NORTHERN PARTS OF THE AREA WHILE ANOTHER BAND CROSSES INTO
WESTERN PARTS OF THE AREA. RAIN HAS NOT YET MADE IT INTO THE KERN
COUNTY MOUNTAINS AND DESERT AREAS HOWEVER THIS WILL CHANGE LATER
TODAY. VANDENBERG RADAR SHOWS A LARGE RAIN BAND STRETCHING WELL
OFFSHORE AND THE ORIENTATION OF THE BAND SEEMS STATIONARY. THIS
SHOULD RESULT IN CONTINUED BANDS OF RAIN MOVING INTO THE FORECAST
AREA. WATER VAPOR SATELLITE IMAGERY SHOWS A COMPLEX AND POTENTIALLY
VERY WET SYSTEM OFF SHORE WITH A DEEP LOW, SEVERAL VORTICITY CENTERS
AND A VERY DEEP TAP OF SUBTROPICAL MOISTURE EXTENDING WELL TO THE
WEST. CURRENTLY, THE AIRMASS IS RATHER WARM WITH SNOW LEVELS RUNNING
ABOVE 8000 FEET IN THE KERN COUNTY AREA AND AROUND 7500 FEET NEAR
YOSEMITE. THESE HIGH SNOW LEVELS MAY BECOME A BIG FACTOR LATER TODAY
AND TONIGHT AS HEAVY RAINS WILL FALL ON A DEEP SNOW PACK IN THE 5500-
7000 FOOT ELEVATIONS. WILL NEED TO MONITOR CLOSELY THE HYDROLOGIC
SITUATION AS FORECAST MODELS KEEP MUCH OF THE AREA IN THE WARM
SOUTHWESTERLY FLOW THROUGH THE NEXT 24 TO 36 HOURS. AT ELEVATIONS
ABOVE 7000 FEET ANOTHER HEAVY SNOW DUMP IS LIKELY AND THE LATEST QPF
FROM THE RIVER FORECAST CENTER IN SACRAMENTO SUGGESTS UP TO 70 OF
NEW SNOW MAY FALL IN THE NEXT 48 HOURS NEAR YOSEMITE AND AROUND 50
IN THE TULARE COUNTY AREA MOUNTAINS. AN A LITTLE CONCERNED ABOUT THE
FLOODING POTENTIAL IN THE KERN COUNTY MOUNTAINS AS WELL SINCE MODEL
QPF FOR THE FRAZIER PARK AREA SHOWS UP TO 3 OF WATER EQUIVALENT
THROUGH EARLY WEDNESDAY. SNOW LEVELS HERE WILL REMAIN HIGH THROUGH
LATE TUESDAY, WHEN COLDER AIR IS PROGGED TO FINALLY ARRIVE. LATEST
RUN OF THE GFS CONTINUES PREVIOUS MODEL RUN PROJECTIONS IN DRIVING
DOWN THE SNOW LEVEL TO AROUND 4000 FEET BY WEDNESDAY MORNING. THIS
WOULD BRING SNOW TO TEJON PASS AND TEHACHAPI PASS HOWEVER THE AMOUNT
OF REMAINING PRECIPITATION WILL BE TRICKY AS THIS WILL OCCUR AS THE
SYSTEM IS EXITING THE AREA. WILL NEED TO CHANGE SOME OF THE WORDING
ON THE WINTER STORM WATCH TO REFLECT A LATER LOWERING OF SNOW LEVELS.
AS FOR THE SIERRA WINTER STORM WARNING, A HEAVY SNOWFALL IS VERY
LIKELY OVER HIGHER ELEVATIONS AS STATED ABOVE. MODELS STILL ARE IN
GOOD AGREEMENT IN THE TIMING OF THE LOW EXITING THE AREA ON
WEDNESDAY. THE POPS FOR WEDNESDAY LOWER QUICKLY AND I WONDER IF MAYBE
THE CHANCES OF RAIN AND THUNDERSTORMS MAY BE A LITTLE HIGHER THAN IN
THE CURRENT GRIDS. WILL LET THE DAY SHIFT TAKE A LOOK AT THE 12Z
MODELS TO MAY ANY CHANGES IF NECESSARY. HAVE ADDED THUNDERSTORMS TO
THE WEDNESDAY FORECAST AS 500 MB TEMPERATURES ARE PROGGED TO FALL TO
-25 CELSIUS. ALL IN ALL A VERY ACTIVE PERIOD OF WEATHER...AGAIN.

.LONG TERM...FOR WEDNESDAY NIGHT THROUGH SUNDAY...GOOD AGREEMENT
AMONG MEDIUM RANGE MODELS IN SHIFTING THE UPPER LOW EAST OVER THE
ROCKIES WEDNESDAY NIGHT. SHORT WAVE RIDGING BUILDS IN BEHIND IT TO
DRY THINGS OUT TEMPORARILY. RIDGE AXIS CROSSES OVER THE DISTRICT
THURSDAY AFTERNOON AS THE NEXT PACIFIC SYSTEM BEARS DOWN ON THE
CALIFORNIA COAST. WELL SEE INCREASING MOISTURE THURSDAY NIGHT WITH
CHANCE POPS RETURNING FOR THE NORTHERN HALF OF THE FA FRIDAY/FRI
NIGHT...WITH OROGRAPHICS AIDING IN THE DEVELOPMENT OF PRECIP OVER
THE SOUTHERN SIERRA. THINK SNOW LEVELS WILL ONLY BOTTOM OUT AROUND
5000 FEET NEAR YOSEMITE WITH THIS SYSTEM. MODELS CONTINUE WITH THE
PROGRESSIVE CYCLE AS THE REGION WILL REMAIN UNDER A MEAN TROUGH
THROUGHOUT THE EXTENDED PERIOD. IT APPEARS ANOTHER BRIEF BREAK ON
SATURDAY BEFORE THE NEXT SHORT WAVE AFFECTS US ON SUNDAY. AFTERNOON
TEMPERATURES WILL REBOUND A FEW DEGREES THURSDAY AS THE COLD UPPER
LOW DEPARTS. THEN LITTLE CHANGE FROM DAY TO DAY UNDER THE WESTERLY
FLOW ALOFT.

&&

.AVIATION...A STORM SYSTEM WILL RESULT IN AREAS OF MVFR CEILINGS IN
RAIN AND MOUNTAIN OBSCURATIONS OVER THE SIERRA NEVADA AND TEHACHAPI
MOUNTAINS. FOR SPECIFIC DETAILS...PLEASE REFER TO TAFS FOR
KMCE...KFAT AND KBFL.

&&

.HNX WATCHES/WARNINGS/ADVISORIES...WINTER STORM WARNING FOR THE
     SOUTHERN SIERRA NEVADA...FROM YOSEMITE TO KINGS CANYON...
     THROUGH TUESDAY NIGHT.
  ...WINTER STORM WARNING FOR THE TULARE COUNTY MOUNTAINS FROM
     TODAY THROUGH TUESDAY NIGHT.
  ...WINTER STORM WATCH FOR THE KERN COUNTY MOUNTAINS TONIGHT
     THROUGH TUESDAY NIGHT.

&&

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