ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 217 PM EDT FRI JUN 20 2014 VALID 12Z TUE JUN 24 2014 - 12Z SAT JUN 28 2014 THIS MEDIUM RANGE PERIOD...THE DOMINANT SYNOPTIC-SCALE FEATURE ALOFT WILL BE A BROAD CIRCULATION AT 500 MILLIBARS. MID-LEVEL ENERGY--OF VARIED INTENSITY--ROTATES AROUND THE BASE OF THE TROUGH...SPREADING ACROSS THE PANHANDLE FROM SOUTH TO NORTH...AND MIGRATING NORTHWESTWARD INTO THE INTERIOR. A SECONDARY SOURCE REGION FOR SENSIBLE WEATHER APPEARS TO ORIGINATE OVER ARCTIC CANADA...WITH SHORTWAVE ENERGY MIGRATING WESTWARD AND OCCASIONALLY ENGAGING RESIDUAL ENERGY RESIDING IN THE GULF OF ALASKA. IN THIS TYPE OF PATTERN---WITH A SUBSTANTIAL RIDGE PLANTED ALONG THE CANADIAN ROCKIES--THE SOUTHEASTERN QUADRANT OF THE CIRCULATION IS WHERE MUCH OF THE ENERGY SHEARS APART AND EJECTS DOWNSTREAM ACROSS SOUTHERN BRITISH COLUMBIA AND SOUTHERN ALBERTA. A PORTION OF THE WEAKENING IMPULSE MIGRATES NORTHWARD ALONG THE PANHANDLE AND ACROSS THE NORTHERN GULF COAST-SOUTHERN INTERIOR AND A PORTION SLIPS EASTWARD INTO SOUTHWEST CANADA. AROUND DAY 5...A MIGRATORY UPPER-LEVEL SYSTEM ALONG 50N LATITUDE SLIDES EAST OF THE DATELINE AND GRADUALLY INFUSES ITS ENERGY INTO THE PARENT CIRCULATION---AND SENDS A MORE-ORGANIZED SHORTWAVE EASTWARD INTO THE PACIFIC NORTHWEST FOR DAY 6. THE DETERMINISTIC CANADIAN...ECMWF AND GFS HAVE THE SCENARIO COVERED...BUT THEIR DETAILS ARE FAR FROM AGREED UPON--WITH RESPECT TO THE ENTRY POINT ALONG THE NORTH AMERICAN COAST. HERE...THE WPC GRAPHICS TOOK A MIDDLE GROUND APPROACH AT THE SURFACE AND ALOFT...WITH THE 20/00Z ECENS-NAEFS MEANS COMPRISING ABOUT 80% OF THE BLENDED SOLUTION AND THE 20/06Z GEFS MEAN COMPRISING THE REMAINING PORTION OF THE FORECAST THROUGH DAY 8. VOJTESAK