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168
FXUS02 KWBC 261557
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1057 AM EST WED NOV 26 2014

VALID 12Z SAT NOV 29 2014 - 12Z WED DEC 03 2014


...HEAVY PRECIPITATION FOR CALIFORNIA...ESPECIALLY MON/TUE...

IN THE MEDIUM RANGE FLOW SPLITS OFF THE WEST COAST OF NORTH
AMERICA. A DEEP SOUTHERN STREAM TROUGH FORMS WEST OF
CALIFORNIA...AND IS EXPECTED TO COME INLAND...ALTHOUGH THE MODELS
VARY IN TIMING. THE NORTHERN STREAM IS ANCHORED BY THE BROAD
CIRCUMPOLAR LOW...HANGING OUT WHERE IT WOULD BE EXPECTED IN
NORTHERN CANADA. BOTH STREAMS ARE CARVING OUT LARGE SCALE
FEATURES...SO THE FORECAST BOILS DOWN TO TWO MAIN EVENTS...THE
NORTHERN STREAM RE-ESTABLISHING ARCTIC AIR ACROSS THE NORTHERN
TIER OF THE U.S...AND THE SOUTHERN STREAM DELIVERING A SOAKING
RAIN AND HEAVY HIGH ELEVATION SNOWS TO MUCH OF CALIFORNIA. SOME OF
THIS EVENT WILL SPILL OVER THE SIERRAS...ESPECIALLY IN THE
NORTHERN ROCKIES THROUGH THIS WEEKEND...AND THEN INTO THE GREAT
BASIN AND SOUTHERN DESERTS NEXT WEEK.

THE WPC FORECAST HAS REMAINED CLOSE TO THE ENSEMBLE
MEANS...ESPECIALLY THE ECMWF ENSEMBLE MEAN WHICH IS OFTEN
PREFERRED FOR ITS DEEPER AND SLOWER SOLUTIONS. IT IS WORTH
NOTING...HOWEVER...THAT RUN TO RUN VARIABILITY IN THE OPERATIONAL
MODELS DOES LOWER CONFIDENCE A BIT...ESPECIALLY AFTER DAY 4. THE
MAIN EFFECTS OF THIS UNCERTAINTY WOULD BE TIMING OF THE WEST COAST
PRECIPITATION...AND TEMPERATURE FORECASTS EAST OF THE ROCKIES. THE
00Z RUNS OF THE ECMWF HAVE BEEN PARTICULARLY DEEP AND SLOW OFF THE
WEST COAST. THE MOST RECENT RUN SEPARATED THE STREAMS SO MUCH THAT
THE NORTHERN STREAM IS ALLOWED TO BECOME VERY DOMINANT OVER THE
CENTRAL AND EASTERN U.S. THIS COLDER FORECAST IS IN STARK CONTRAST
TO RECENT 12Z RUNS OF THE SAME MODEL WHICH WERE MUCH MORE MILD.
THE GFS HAS BEEN MORE CONSISTENT...BUT IS TOO LITTLE AMPLIFIED AND
TOO PROGRESSIVE BY DAYS 5-7. FOR THIS CYCLE WE WERE ABLE TO
INCORPORATE SOME OF THE 06Z GEFS MEAN...WHICH IS DEEPER...BUT IT
TOO FAILS TO CAPTURE THE LIKELY DEPTH OF THE CALIFORNIA TROUGH. A
BETTER OPTION WAS THE 06Z PARALLEL GFS WHICH FIT VERY WELL WITH
THE 00Z ECMWF ENSEMBLE MEAN AND WITH WPC CONTINUITY. THE 06Z
OPERATIONAL GFS WAS A BETTER FIT EAST OF THE ROCKIES EARLY IN THE
PERIOD WHEN ARCTIC AIR IS BECOMING RE-ESTABLISHED.

AT A QUICK GLANCE...OUR PLAN WILL BE TO MAINTAIN WPC CONTINUITY TO
QPF...WHICH IS ALREADY TOWARD THE HIGHER END OF THE AVAILABLE
GUIDANCE. CERTAINLY THE PATTERN IS FAVORABLE FOR CALIFORNIA...AND
THE PRECIPITATION WILL BE WELCOMED...AND SHOULD HIT THE SIERRAS
WITH HEAVY SNOW. BUT CERTAIN MEASURES SUCH AS MOISTURE FLUX AND
PRECIPITABLE WATER ANOMALIES DO NOT SHOW THIS TO BE AN
EXCEPTIONALLY ANOMALOUS STORM. SEVERAL ADDITIONAL SUCH STORMS
WOULD BE NEEDED TO PROVIDE DROUGHT RELIEF.

BURKE
$$






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