EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 228 AM EDT THU JUN 12 2014 VALID 12Z SUN JUN 15 2014 - 12Z THU JUN 19 2014 ...OVERVIEW... THE FLOW PATTERN OVER THE LOWER 48 DURING THIS MEDIUM RANGE PERIOD WILL BE DOMINATED BY A FAIRLY PROGRESSIVE CANADIAN STORM TRACK FROM SOUTHERN BRITISH COLUMBIA TO NORTHERN LABRADOR. THE RATHER PROGRESSIVE PATTERN WILL FEATURE TWO NOTABLE CANADIAN AIRMASS INTRUSIONS...MOVING THROUGH THE DAKOTAS...UPPER GREAT LAKES AND MIDWEST ON SUNDAY AND MONDAY---FOLLOWED BY A SECOND FRONTAL PASSAGE MOVING THROUGH THE NORTHERN PLAINS NEXT WEDNESDAY AND THURSDAY. IN A BROAD DESCRIPTIVE MANNER...BOTH FRONTAL PASSAGES WILL MODIFY AND 'FLATTEN OUT' ALONG THE I-80/I-70 CORRIDOR FROM THE DIVIDE EASTWARD TO THE ATLANTIC COAST LINE. ...MODEL PREFERENCES/UNCERTAINTY ASSESSMENT... THE MEDIUM RANGE PACKAGE MAINTAINED RATHER GOOD CONTINUITY USING A BLEND OF THE 11/12Z NAEFS-GEFS-ECENS MEANS SOLUTIONS THROUGH DAY 5. THE BIGGEST CHALLENGE EARLY ON IN THIS STRING OF 7 IN-A-ROW WAS TO BE PATIENT WITH THE RUN-TO-RUN MODEL ADJUSTMENTS OVER CENTRAL CANADA---EVENTUALLY...SETTLING ON A STORM TRACK ACROSS CANADA---ONE THAT WOULD RESPECT A BLOCKY RIDGE AXIS IN THE DAVIS STRAIT...RIDGING ALONG 53N 100W AND BROAD SUBTROPICAL RIDGE OVER NORTHERN MEXICO. BACK ON SATURDAY (AND THE 6/12Z CYCLE)...THE NAEFS AND GEFS ENSEMBLES WERE THEN...AND EVEN NOW...DECENT IF NOT BETTER PIECES OF GUIDANCE CONCERNING ALL THREE...AND GENERALLY HAVE HANDLED THE INITIAL PACIFIC TROUGH MIGRATION THROUGH THE NORTHERN ROCKIES AND NORTHERN HIGH PLAINS WITH BETTER CONSISTENCY AND LESS IMPACT DOWNSTREAM OVER ATLANTIC CANADA VERSUS THE ECENS/ECMWF. IN FACT FOR THIS PACKAGE...I COULDNT UTILIZE MUCH MORE THAN 30 PCT OF THE 11/12Z ECENS MEAN THROUGH DAY 7...AND HAD TO BASICALLY THROW OUT THE DETERMINISTIC 11/12Z ECMWF AT THE BEGINNING OF DAY 3 FOR FAILING TO HANDLE ALL THREE RIDGES IN EQUALLY POOR FASHION OVER NEARLY ALL OF NORTH AMERICA. THE DETERMINISTIC 11/12Z GFS SEEMED VERY REASONABLE OVER THE WEST...THE ENTIRE PLAINS STATES AND DOWNSTREAM INTO THE OHIO VALLEY-PIEDMONT AND MID-ATLANTIC REGION PRACTICALLY INTO DAY 6. FROM THIS VANTAGE POINT...WHAT WE SHOULD BEGIN TO SEE AROUND 17/12Z AT 500 MBS (MID-POINT DAY 5) OVER ATLANTIC CANADA IS WHAT THE NAEFS...NOT THE ECENS PROJECTS WILL OCCUR...IE MEAN RIDGE OVER THE YUKON...A BLOCKY RIDGE OVER LABRADOR AND THE DAVIS STRAIT...AND A BROAD RIDGE OVER THE SOUTH. THAT SHOULD BE A STABLE FORECAST THROUGH DAY 7...WITH THE SECOND PACIFIC TROUGH MIGRATING EASTWARD THROUGH THE NORTHERN TIER. THE 11/12Z NAEFS/GEFS KEPT THE PATTERN FAIRLY SIMPLE AND STRAIGHT-FORWARD ACROSS SOUTHERN CANADA. ...SENSIBLE WEATHER HIGHLIGHTS... COOL IN THE PACIFIC NORTHWEST AND UNSETTLED IN THE NORTHERN ROCKIES AND NORTHERN HIGH PLAINS. ABOVE NORMAL PRECIPITATION IS ANTICIPATED FOR THE NORTHERN PLAINS...THE PLATTE VALLEY AND THE UPPER MISSISSIPPI BASIN. A RATHER PERSISTENT NOCTURNAL RAINFALL MAXIMA WILL BE OBSERVED ALONG THE LOWER HALF OF THE MISSOURI VALLEY...MID-MISSISSIPPI VALLEY AND UPPER GREAT LAKES THIS MEDIUM RANGE PERIOD. ISOLATED DRY LINE CONVECTION SHOULD BE A ROUTINE FEATURE OF THIS PATTERN FROM NORTHEAST NEW MEXICO INTO SOUTHWEST NEBRASKA. HOT AND HUMID FOR THE SOUTHEAST QUARTER OF THE NATION. SUBTROPICAL MOISTURE WILL BE ON THE INCREASE OVER THE UPPER RIO GRANDE VALLEY ALONG THE WESTERN PERIPHERY OF A BROAD RIDGE CENTERED OVER NORTHERN MEXICO...AND A MIXED BAG OF CLOUDS AND SUN FOR THE GREAT LAKES AND NORTHEAST AS THE UPPER-LEVEL FLOW CARRIES SIGNIFICANT PERIODS OF CONVECTIVE CLOUD DEBRIS AND OCCASIONAL REMNANT MCS PRECIPITATION/VORTICITY ALONG THE MIGRATORY COLD FRONT(S). VOJTESAK