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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1804Z Jul 14, 2014)
 
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
204 PM EDT MON JUL 14 2014

VALID 12Z FRI JUL 18 2014 - 12Z TUE JUL 22 2014

THERE IS GOOD AGREEMENT/CONTINUITY WITH THE PERSISTENCE OF A LARGE
SCALE MEAN TROUGH ALIGNED JUST WEST OF THE MAINLAND THROUGH THE
PERIOD.  WITHIN THIS FEATURE A LEADING SHRTWV TROUGH NEARING OR
REACHING THE WEST COAST AS OF 12Z FRI SHOULD CONTINUE ACROSS THE
MAINLAND DURING THE FIRST HALF OF THE FCST AS UPSTREAM ENERGY
CROSSING SIBERIA REINFORCES THE OVERALL TROUGH.  THERE IS
REASONABLE CONSENSUS AMONG GFS/ECMWF RUNS AND ENSEMBLE MEANS WITH
THIS LEADING SHRTWV... WITH RECENT TRENDS BEING TOWARD A DEEPER
FEATURE AND A FARTHER SEWD PUSH OF THE LEADING COLD FRONT. 
UPSTREAM DETAILS DIVERGE AS EARLY AS DAY 5 SAT.  THUS CONFIDENCE
IN OPERATIONAL MODEL DETAILS BECOMES FAIRLY LOW FROM THAT POINT
ONWARD THOUGH THE 00Z ECMWF IS JUST CLOSE ENOUGH TO THE MEANS TO
ALLOW MAINTENANCE OF 20 PCT WEIGHTING TO PROVIDE MODEST DETAIL
ENHANCEMENT RELATIVE TO THE MEANS.  ENSEMBLE MEANS HAVE BEEN MORE
STABLE AND SIMILAR THAN AVERAGE OVER THE PAST COUPLE DAYS... WITH
THE ECMWF MEAN/NAEFS MEAN ULTIMATELY PREFERRED BASED ON THE 06Z
GEFS MEAN PSBLY TRACKING SFC LOW PRES TOO FAR N OF THE MAINLAND BY
DAYS 7-8 MON-TUE.

AHEAD OF THIS MEAN TROUGH GUIDANCE IS STILL HAVING SOME DIFFICULTY
WITH THE SYSTEM FCST TO TRACK OVER THE NERN PAC ON DAY 4 FRI.  THE
ONE IMPROVEMENT FROM 24 HRS AGO IS MORE AGREEMENT TOWARD A SFC LOW
TRACK TO THE S OF THE MAINLAND.  AS WAS THE CASE YDAY THE 06Z/12Z
GFS AND 06Z GEFS MEAN STRAY TO THE FAST SIDE OF THE SPREAD WHILE
THE 00Z GFS IS MORE COMPARABLE TO THE 00Z ECMWF.  IN THE INTEREST
OF KEEPING CONTINUITY CHANGES MODEST... PREFER A SOLN CLOSEST TO
THE 00Z GFS/ECMWF.  00Z CMC/UKMET TRENDS SHOW THAT SOMEWHAT FASTER
TIMING IS PSBL.  THE 12Z CMC REMAINS FASTER BUT THE 12Z UKMET HAS
ADJUSTED MUCH SLOWER SO THE 00Z GFS/ECMWF LOOKS BEST FOR NOW.

THERE ARE STILL INDICATIONS THAT A W-CNTRL PAC UPR LOW SHOULD OPEN
UP AND PSBLY BRUSH THE ALEUTIANS MID-LATE PERIOD.  THE 00Z/12Z GFS
RUNS ARE ON THE SLOW SIDE OF THE SPREAD WHILE THE 00Z CMC IS
FASTEST.  WEAKENING NATURE OF THIS FEATURE SHOULD LEAD TO ONLY A
MODEST SFC REFLECTION.

DAY 4 FRI IS WEIGHTED PRIMARILY TOWARD THE 00Z GFS/ECMWF BASED ON
NERN PAC PREFS.  UPSTREAM ISSUES LEAD TO REMOVAL OF THE 00Z GFS
AFTER EARLY DAY 5 SAT... WITH A 60/20/20 BLEND OF THE 00Z ECMWF
MEAN/NAEFS MEAN/ECMWF OFFERING THE BEST REPRESENTATION OF ENSEMBLE
MEAN AGREEMENT WITH SLIGHT DETAIL ENHANCEMENT FOR THE REST OF THE
PERIOD.

RAUSCH