EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1159 AM EDT TUE JUL 19 2016 VALID 12Z FRI JUL 22 2016 - 12Z TUE JUL 26 2016 ...GENERAL OVERVIEW AND MODEL EVALUATION... A PAIR OF SHORTWAVES CROSSING THE NORTHERN TIER...NORTH OF AN UPPER RIDGE SUPPRESSED OVER THE SOUTHERN HALF OF THE NATION...WILL BE THE MAIN FOCUS OF THE FORECAST THIS WEEKEND AND INTO EARLY NEXT WEEK. THE FIRST SHORTWAVE SHOULD TRACK TROUGH THE NORTHEAST ON SATURDAY BEFORE PIVOTING INTO SOUTHEAST CANADA ON SUNDAY...WHILE THE SECOND IS EXPECTED TO STEADILY PROGRESS FROM THE PACIFIC NORTHWEST TO THE NORTHERN PLAINS THIS WEEKEND. THE GREATEST MODEL SPREAD AND UNCERTAINTY IN THE FORECAST OVER THE LOWER 48 IS WITH THE SECOND SHORTWAVE...ESPECIALLY AS IT POSSIBLY SLOWS DOWN AND AMPLIFIES OVER THE GREAT LAKES EARLY NEXT WEEK. THE 00Z ECMWF IS CURRENTLY ADVERTISING A SLOWER/MORE AMPLIFIED SOLUTION THAN THE 00Z GEFS/GFS/ECMWF ENSEMBLE MEAN...BUT SINCE THE 00Z CMC/UKMET...A GENERAL SLOWING TREND IN THE ENSEMBLES...AND CONTINUITY WOULD ALL SUPPORT A SOLUTION CLOSER TO THE 00Z ECMWF...THE LATEST WPC DAY 3-7 FORECAST WAS WEIGHTED SLIGHTLY MORE TOWARDS THE ECMWF/ECMWF ENSEMBLE MEAN. GERHARDT