EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1126 AM EDT SUN JUN 28 2015 VALID 12Z WED JUL 01 2015 - 12Z SUN JUL 05 2015 ...OVERVIEW... AN AMPLIFIED FLOW PATTERN ALOFT IS EXPECTED TO PREVAIL ACROSS THE NORTH AMERICA WITH AN UPPER-LEVEL ANTICYCLONE SLOWLY MIGRATING NORTHWESTWARD FROM THE CENTRAL GREAT BASIN TO THE PACIFIC NORTHWEST COAST. THIS AMPLIFIED PATTERN WILL SET UP A VERY WARM TO HOT PATTERN BENEATH THE ANTICYCLONE AND A COOLER...CLOUDIER AND WET PATTERN DOWNSTREAM WITHIN THE TROUGH. THE UPPER-LEVEL ANTICYCLONE OVER THE GREAT BASIN IS IMPRESSIVE FOR LATE JUNE WITH THE PERSISTENT 594+ DM CENTER AT 500 MB EXPECTED TO PERSIST INTO DAY 5--- BEFORE A PACIFIC SYSTEM AND AN ONSHORE FLOW MIGRATING ACROSS THE ALASKA PANHANDLE AND SOUTHWEST CANADA--- SPREADS INTO THE PACIFIC NORTHWEST AND WEAKENS THIS ANTICYCLONE. A BROAD UPPER-LEVEL CYCLONE OVER NORTHERN HUDSON BAY WILL KEEP A TROUGH POSITIONED OVER THE LOWER 48 --- PRIMARILY EAST OF THE CONTINENTAL DIVIDE. THE NORTHWEST FLOW PATTERN EXPECTED ACROSS THE NORTHERN PLAINS WILL MIGRATE A SERIES OF MID-LEVEL DISTURBANCES SOUTHEASTWARD FROM WEST CENTRAL CANADA ACROSS THE MISSOURI VALLEY...THE UPPER GREAT LAKES AND MID-MISSISSIPPI VALLEY. THESE DISTURBANCES SHOULD MIGRATE THROUGH THE BASE OF THE PERSISTENT TROUGH---WITH PERIODS OF CLOUDS AND RAINFALL CHANNELING EASTWARD ACROSS THE OHIO VALLEY...CENTRAL APPALACHIA AND THE NORTHEAST --- BEFORE EXITING INTO THE WESTERN ATLANTIC OCEAN BASIN. ...MODEL PREFERENCES/UNCERTAINTY ASSESSMENT... FOR THIS PARTICULAR MEDIUM RANGE PERIOD --- JULY 1-5 --- CURRENT ENSEMBLE MODEL GUIDANCE MAINTAINS THE 'AMPLIFIED THEME' AND MIGRATORY STORM TRACK OVER THE EASTERN HALF OF NORTH AMERICA...AND THUS FORMED THE BASIS OF THE NATIONAL GUIDANCE USED THIS PACKAGE...WITH ABOUT 60 PERCENT OF THE 00Z ECMWF ENSEMBLE MEAN...AND 20 PERCENT EACH 06Z GEFS MEAN AND 00Z NAEFS MEAN. AT LEAST EARLY IN THE PERIOD...THERE IS SUFFICIENT ENSEMBLE MEMBER AND DETERMINISTIC SUPPORT TO USE ABOUT 40 PERCENT OF THE 06Z GFS AND 00Z ECMWF WITH THE ENSEMBLES...PARTICULARLY WITH LOW PRESSURE OVER THE MIDWEST INTO THE OHIO VALLEY...ALTHOUGH THE GFS MAY BE TOO DEEP AND NORTH. OTHERWISE...BEYOND DAY 5 WITH THE UPPER CYCLONE LIKELY ENTERING WESTERN CANADA...A SHIFT COMPLETELY TOWARD THE ENSEMBLE MEANS IS USED AS THE SPREAD BECOMES TOO HIGH TO ACCOUNT FOR REASONABLY WELL WITH THE DETERMINISTIC SOLUTIONS. CONFIDENCE IS ABOUT AVERAGE THROUGH DAY 5...THEN IS BELOW AVERAGE. ...SENSIBLE WEATHER HIGHLIGHTS... THE STRONG UPPER-LEVEL RIDGE AXIS WILL MAINTAIN WELL-ABOVE NORMAL TEMPERATURES ACROSS MUCH OF THE WEST WITH A NOMINAL COOLING TREND PROVIDED BY PERIODS OF HIGH-BASED CONVECTION ROTATING CLOCKWISE AROUND THE PERIPHERY OF THE ANTICYCLONE. A DISPLACEMENT OF THE UPPER-LEVEL RIDGE IS ANTICIPATED ALONG THE PACIFIC NORTHWEST COAST NEXT WEEKEND---WITH SOME RELIEF IN TEMPERATURES FELT LOCALLY ALONG THE IMMEDIATE COAST AS STRATUS EXPANDS BENEATH THE THERMAL TROUGH. CONVECTIVE ACTIVITY AND THE MIGRATORY NATURE OF THE PRECIPITATION DISTRIBUTIONS TAKE ON A 'SEASONAL PATTERN' --- WITH NOCTURNAL PRECIPITATION MAXIMIZED ACROSS THE LOWER HALF OF THE MISSOURI VALLEY AND CENTRAL PLAINS. MORE OF A LATE-NIGHT AND EARLY-MORNING DISTRIBUTION OF HEAVIER RAINFALL IS ANTICIPATED ACROSS THE MID-MISSISSIPPI VALLEY...THE OHIO VALLEY...GREAT LAKES AND THE CENTRAL APPALACHIANS ---IN RESPONSE TO THE POTENTIAL FOR ORGANIZED CONVECTIVE CLUSTERS AND MCS DEVELOPMENT TO MIGRATE DOWNSTREAM --- IN THE 'PROJECTED' UPPER-LEVEL SYNOPTIC-SCALE PATTERN. VOJTESAK/JAMES