Prognostic Meteorological Discussion
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000
FXUS02 KWBC 251545
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1044 AM EST TUE NOV 25 2014

VALID 12Z FRI NOV 28 2014 - 12Z TUE DEC 02 2014

...CHANCES INCREASING FOR HEAVY PRECIPITATION ACROSS MUCH OF
CALIFORNIA...

...WEST...
TROUGHING WAS ALREADY BECOMING ESTABLISHED IN THE EASTERN
PACIFIC...NORTHEAST OF HAWAII. WHILE THE LONGWAVE PATTERN APPEARS
FAIRLY STABLE...A TANDEM OF NORTHERN AND SOUTHERN STREAM
SHORTWAVES EMANATING FROM ASIA WILL ACT TO AMPLIFY THE EXISTING
LONGWAVE FEATURES...INCLUDING THE EASTERN PACIFIC TROUGH. THIS
TAKES PLACE BETWEEN DAYS 3 AND 5...OVER THE UPCOMING
WEEKEND...RESULTING IN A LARGE AND DEEP TROUGH...2 TO 3 STANDARD
DEVIATIONS BELOW CLIMATOLOGY AT 500 MB...THAT WILL MIGRATE INTO
THE WESTERN U.S.

THE OPERATIONAL MODELS VARY AS TO THE DEPTH AND FORWARD
PROGRESSION OF THE TROUGH...BUT ALL YIELD WIDESPREAD
PRECIPITATION...PARTICULARLY FOCUSED ON NORTHERN AND CENTRAL
CALIFORNIA...BUT ALSO REACHING SOUTHERN CALIFORNIA BY MON/TUE OF
NEXT WEEK. DEEPER SOLUTIONS SUCH AS THE 00Z ECMWF AND 06Z GFS
WOULD MEAN A LONGER DURATION EVENT AND GREATER PRECIPITATION
AMOUNTS...ESPECIALLY FOR SOUTHERN CALIFORNIA WHERE THE EVENT
TOTALS WILL BE MORE SENSITIVE TO THE DEPTH OF THE SYSTEM. THE 00Z
ECMWF WAS ONE OF THE DEEPEST AND SLOWEST SOLUTIONS AMONG THE
MODELS AND ENSEMBLES. THE ENSEMBLE MEANS...HOWEVER...HAVE BEEN
TRENDING DEEPER AND SLOWER.

THE MODELS SHOW DECENT AGREEMENT AS TO QPF...AND ARE SPATIALLY
CONSISTENT WITH THE ENSEMBLE MEANS. FOR THE PERIOD ENDING 00Z ON
DECEMBER 03...EXPECTATIONS ARE GENERALLY FOR 2-4 INCHES OF
RAINFALL ALONG THE FULL LENGTH OF THE CALIFORNIA COAST...TAPERING
OFF TOWARD LESSER AMOUNTS SOUTH OF LOS ANGELES. WITH EARLIER ONSET
AND LONGER DURATION...ANALOG EVENTS BASED ON THE GEFS RE-FORECAST
DATA SUGGEST 6 TO 8 INCHES OF LIQUID EQUIVALENT IN THE FAVORABLE
LOCATIONS OF THE CENTRAL AND NORTHERN SIERRA AND NORTHERN
CALIFORNIA COASTAL RANGE. THE 06Z PARALLEL GFS BACKS THIS UP...AND
IT IS LIKELY THAT THE MOST FAVORABLE LOCATIONS IN THE TERRAIN
WOULD SEE LOCALLY HIGHER AMOUNTS. THE LATE PORTION OF THE FORECAST
IS A WET PERIOD IN GENERAL ALONG AND WEST OF THE CONTINENTAL
DIVIDE...WITH SNOWS PILING UP IN THE HIGH COUNTRY AND RAIN IN THE
LOWER ELEVATIONS.

...EAST...
EAST OF THE DIVIDE...THE MAIN CHALLENGE IS AN ARCTIC FRONT THAT
SLIDES THROUGH THE NORTHERN HALF OF THE U.S. DESPITE UNFAVORABLY
MILD...WESTERLY UPPER FLOW. THE COLD AIR SLIDES MAINLY THROUGH THE
NORTHERN U.S...WHILE THE TAIL END OF THE FRONT BECOMES QUICKLY
MODIFIED OVER THE SOUTHERN PLAINS.

...MODEL PREFERENCE...
THOUGH WE REMAIN CENTERED AROUND A 00Z ECMWF ENSEMBLE MEAN
SOLUTION...WE INCORPORATED THE 00Z ECMWF...UKMET...AND 06Z GFS AT
TIMES TO RESOLVE THE SURFACE LOWS ACCOMPANYING OUR ARCTIC FRONT IN
THE EAST AND PACIFIC FRONT IN THE WEST. OUR BLEND RESULTED IN A
SLIGHTLY FASTER ARCTIC INTRUSION OVER THE CENTRAL PLAINS AND
MIDWEST.

BURKE

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