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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1557Z Jul 18, 2014)
 
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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
1157 AM EDT FRI JUL 18 2014

VALID 12Z MON JUL 21 2014 - 12Z FRI JUL 25 2014

...OVERVIEW...

A DEEP UPPER LOW WILL DROP SOUTH FROM THE GULF OF ALASKA EARLY
NEXT WEEK BEFORE PROGRESSING INLAND OVER BRITISH COLUMBIA AS IT
APPROACHES AN UPPER RIDGE EXPANDING OVER THE CENTRAL PLAINS/FOUR
CORNERS REGION.  ENERGY ROUNDING THE NORTHERN EDGE OF THE BUILDING
RIDGE AT THE START OF THE FORECAST PERIOD WILL PLAY AN IMPORTANT
ROLE IN THE FORECAST AS IT AMPLIFIES OVER THE GREAT LAKES/MIDWEST
TOWARDS THE MIDDLE OF NEXT WEEK...REPLACING AN UPPER TROUGH
LIFTING OUT OF THE EASTERN U.S. EARLIER IN THE WEEK.


...GUIDANCE EVALUATION/PREFERENCES... 

THE WPC FORECAST STARTED WITH A BLEND OF THE ECMWF/ECMWF ENSEMBLE
MEAN IN ORDER TO ACCOUNT FOR SOME OF THE LINGERING NOISE WITH THE
ELONGATED TROUGH LIFTING OUT OF THE EASTERN U.S. EARLY NEXT WEEK. 
THE GFS WAS ELIMINATED FROM THE MODEL PREFERENCE SINCE IT DIVES
THE UPPER LOW DROPPING DOWN FROM THE GULF OF ALASKA CONSIDERABLY
FARTHER SOUTH ALONG THE NORTHWEST COAST THAN OTHER DETERMINISTIC
GUIDANCE.

TOWARDS THE MIDDLE TO END OF NEXT WEEK...A LOT OF UNCERTAINTY
STILL REMAINS WITH ENERGY ROUNDING THE RIDGE AND AMPLIFYING OVER
THE GREAT LAKES/MIDWEST.  THE LATEST RUNS OF THE GFS SUGGEST
PHASING THE ENERGY WITH A WEAK SHORTWAVE DIVING DOWN THROUGH
CANADA...CLOSING OFF AN UPPER LOW JUST SOUTH/SOUTHEAST OF THE
HUDSON BAY BY THURSDAY.  MEANWHILE...THE ECMWF HAS BEEN FAVORING
THE IDEA OF KEEPING THE ENERGY SEPARATE AND HOLDS IT
BACK/AMPLIFIES IT OVER THE GREAT LAKES/OHIO VALLEY LATE NEXT WEEK.
 THE LESS PROGRESSIVE/NOT PHASED SOLUTION HAS SUPPORT FROM THE
LATEST CANADIAN RUN AND SOME INDIVIDUAL ENSEMBLE MEMBERS...SO THE
WPC FORECAST RELIED HEAVILY ON THE ECMWF ENSEMBLE MEAN BY THE END
OF THE FORECAST PERIOD...WHICH LEANS SLIGHTLY IN THE DIRECTION
MORE AMPLIFICATION OVER THE GREAT LAKES/OHIO VALLEY...BUT IS NOT
AS EXTREME AS THE ECMWF/CANADIAN.    
   

GERHARDT