EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1154 AM EDT MON AUG 25 2014 VALID 12Z THU AUG 28 2014 - 12Z MON SEP 01 2014 ...OVERVIEW... PROGRESSIVE FLOW PREVAILS ACROSS THE NORTH AMERICAN CONTINENT THIS MEDIUM RANGE PATTERN...BASED UPON THE SIGNAL FOR PERSISTENT OF DEEP TROUGHING IN THE BERING SEA/GULF OF ALASKA AND PROJECTED 250MB JET AXIS STREAKING ACROSS THE PACIFIC NORTHWEST LATE IN THE FORECAST PERIOD. ...MODEL PREFERENCES/GUIDANCE ASSESSMENT... 25/00Z MODELS AND ENSEMBLES WERE IN MUCH BETTER AGREEMENT OVER CANADA AND THE PROGRESSIVE NATURE OF THE FLOW PATTERN ACROSS THE GULF OF ALASKA AND DOWNSTREAM INTO THE LOWER 48 THIS MEDIUM RANGE PERIOD. DAY 3 BEGINS WITH A FRONTAL PASSAGE LINING UP ALONG THE EAST COAST...AND FOLLOWED BY A PAIR OF WELL-DEFINED UPPER-LEVEL SYSTEMS TRACKING FROM WEST TO EAST ACROSS THE CONTINENT. THE 25/00Z DETERMINISTIC GFS LOOKED A TAD BIT FASTER WITH THE MID-LEVEL FLOW ON DAY 5-6 ACROSS THE GREAT BASIN AND DOWNSTREAM OVER KANSAS AND MISSOURI--ALONG I-70 CORRIDOR. THIS SOLUTION TAKES ON MORE TROPICAL MOISTURE AND MID-LEVEL INSTABILITY FROM A REMNANT 'MARIE' THAN OTHER SOLUTIONS. HOWEVER...IT HAS CARRIED THIS SOLUTION FOR THE BETTER PART OF A WEEK AND CANNOT BE TOTALLY RULED OUT. THE 25/00Z DETERMINISTIC ECMWF IS THE SLOWEST SOLUTION...FOCUSING MORE ON THE ENERGY ASSOCIATED WITH THE 250MB JET NOSING INTO THE NORTH CENTRAL ROCKIES FROM THE WEST. THE 25/00Z DETERMINISTIC CANADIAN/UKMET BLENDING MORE GULF MOISTURE INTO THE MIX ALONG THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE. THOUGHT THE 60/20/20 WEIGHTING PREFERRED BY THE MIDSHIFT--WAS EASILY PRESERVED BY A SIMILAR RATIO OF THE 25/12Z ECMWF-NAEFS-GEFS MEANS BEYOND DAY 5. THIS MAINTAINS VERY CONTINUITY WITH THE PATTERN ALOFT AND ITS SEQUENCE OF BROAD-SCALE MIGRATORY MID-LATITUDE WAVES--FROM WEST TO EAST. HOPING THE FINER DETAILS OF THE DETERMINISTIC RUNS--GIVEN ANOTHER CYCLE OR 2--WILL GRASP THE SCOPE OF THE MOISTURE PROFILES AND COME INTO BETTER AGREEMENT FROM CALIFORNIA EASTWARD INTO THE SOUTHERN PLAINS. ...SENSIBLE WEATHER HIGHLIGHTS... THE EXITING EAST COAST COLD FRONT ON DAY 3 WILL BRIEFLY RECONFIGURE THE SUBTROPICAL RIDGE AXIS OVER THE SOUTHEAST...ALLOWING FOR A LESS HUMID AIRMASS TO MOVE INTO THE SOUTHEASTERN STATES. THE PAIR OF PACIFIC FRONTS MIGRATING ACROSS THE CONTINENT WILL FURTHER DAMPEN THE RIDGE...NOT DESTROY IT...BUT FORCE ITS MID-LEVEL AXIS TO WEAKEN IN THE WESTERN PORTION OF THE GULF OF MEXICO AND MISS DELTA REGION THIS FORECAST PERIOD. HIGHEST PROBABILITIES OF PRECIPITATION WILL FOLLOW THE PACIFIC SHORTWAVE THROUGH THE CENTRAL PLAINS AND UPPER GREAT LAKES DAYS 3-5--AND THE NEXT PACIFIC TROUGH MOVING INTO WEST CENTRAL COAST OF CANADA AND NORTHWEST STATES...AFTER DAY 5. THERE REMAINS A SMALL WINDOW OF OPPORTUNITY FOR REMNANT UPPER-LEVEL TROPICAL MOISTURE FROM 'MARIE' TO BECOME ENTRAINED IN THE WESTERLIES--ALONG THE CALIFORNIA COAST--AROUND DAY 5 AND DAY 6. VOJTESAK