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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0613Z Apr 19, 2015)
 
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
213 AM EDT SUN APR 19 2015

VALID 12Z WED APR 22 2015 - 12Z SUN APR 26 2015

...OVERVIEW...
THIS MEDIUM RANGE PERIOD---THE PRIMARY SYNOPTIC-SCALE WEATHER
FEATURES AFFECTING THE LOWER 48 WILL BE: A SLOW-MOVING UPPER-LEVEL
CIRCULATION IN SOUTHEAST CANADA---A PERSISTENT WEST-SOUTHWESTERLY
JET-LEVEL WIND CORE EXTENDING FROM WEST TEXAS TO THE
DELMARVA...AND AN ACTIVE PACIFIC TROUGH.

...MODEL PREFERENCES...
MASS FIELD SOLUTIONS FROM THE 18/12Z ECENS AND NAEFS ENSEMBLE
MEANS BEST FIT THE PREFERRED MEDIUM RANGE FLOW PATTERN FOR THE
LOWER 48. IMMEDIATELY DOWNWIND OF THE SOUTHERN ROCKIES BETWEEN
DAYS 4-5---THE 18/12Z GEFS MEAN IS A FASTER...LESS-AMPLIFIED
SOLUTION CONCERNING LEAD MID-LEVEL PACIFIC ENERGY EJECTION FROM
SOUTHWEST KANSAS TO NORTHERN ILLINOIS---WHILE THE 18/18Z GEFS MEAN
SOLUTION HAS TRENDED SLOWER AND DEEPER FOR DAYS 4-5---DOWNWIND OF
THE SOUTHERN ROCKIES AND IN THE GREAT BASIN. THE 18/18Z GEFS MEAN
IS A SLOWER SOLUTION THAN ITS 18/12Z PACKAGE ACROSS EASTERN CANADA
WITH THE GRADUAL ELONGATION OF THE UPPER-LEVEL CIRCULATION---BUT
CLOSELY FIT THE 18/12Z NAEFS (FOR THE TIME FRAME BETWEEN 24/12Z
AND 26/12Z).

...UNCERTAINTY ASSESSMENT...
PREFER TO SEE MORE OF A 'NEGATIVE-TILT' TROUGH AXIS SOLUTION
BETWEEN 110W-120W LONGITUDE---WHICH WOULD TEND TO PRODUCE A SLOWER
PROGRESSION OF THE PACIFIC TROUGH BY THE END OF THIS DAY 3-7
FORECAST PERIOD. AS IT STANDS---THE 18/12Z ECENS...NAEFS AND GEFS
MEANS ALLOW THE BASE OF THE PACIFIC TROUGH TO MIGRATE IN
PROGRESSIVE FASHION TO 35N 115W (NORTHERN ARIZONA). CANNOT ARGUE
WITH THAT GUIDANCE.  

THE 18/12Z DETERMINISTIC GFS/ECMWF WERE IN DECENT AGREEMENT ALONG
THE WEST COAST AND LOWER COLORADO RIVER VALLEY---BUT NOT PERFECT
AGREEMENT WITH THE SEQUENCING OF MID-LEVEL ENERGY DIGGING INTO THE
TROUGH AXIS ALONG THE CALIFORNIA COAST. THIS LED TO TIMING
DIFFERENCES DOWNSTREAM OVER THE CENTRAL PLAINS. WITH THE 18/12Z
CANADIAN AND NAVGEM CONTINUING TO MAINTAIN DISTINCT CUTOFF LOW
SOLUTIONS OFF THE PACIFIC NORTHWEST COAST FOR DAYS 4-5---AND VERY
DIFFERENT FROM THE GFS/ECMWF---WOULD SUGGEST THAT THERE STILL IS
ENOUGH SPREAD ALONG 125W LONGITUDE---TO 'BROAD BRUSH' THE ENERGY
ENTERING THE WEST COAST---AND THE NORTHEAST-MOVING SHORTWAVE
MIGRATIONS DOWNSTREAM ACROSS THE SOUTH CENTRAL PLAINS AND
MID-MISSISSIPPI VALLEY.

...SENSIBLE WEATHER HIGHLIGHTS...
ACTIVE AND AT TIMES 'CHILLY' APRIL WEATHER PATTERN WILL FOLLOW A
SLOW-MOVING CLOSED LOW MIGRATION ACROSS SOUTHEASTERN CANADA AND
THE NORTHEAST. THIS WILL SETUP BELOW NORMAL HIGH TEMPERATURES
ACROSS THE NORTHEAST QUARTER OF THE NATION.

IN THE WEST...AN ACTIVE SPRING WEATHER PATTERN COMES TO THE
SIERRA...CENTRAL AND SOUTHERN CALIFORNIA...AND DOWNSTREAM ACROSS
THE COLORADO RIVER BASIN AND SOUTHERN ROCKIES WITH THE UPPER-LEVEL
TROUGH DIGGING SOUTHEASTWARD INTO CALIFORNIA.

PRECIPITATION FOCUS EAST OF THE CONTINENTAL DIVIDE WILL FOCUS
ALONG/BENEATH THE WEST-SOUTHWESTERLY ORIENTED JET STREAM
AXIS---AND ALONG A SERIES OF STATIONARY OR DECAYING COLD FRONTS
WHICH ORIGINATE FROM THE UPPER-LEVEL CIRCULATION ANCHORED OVER
SOUTHERN QUEBEC PROVINCE.

VOJTESAK