EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 258 AM EDT TUE JUN 27 2017 VALID 12Z FRI JUN 30 2017 - 12Z TUE JUL 4 2017 ***PATTERN OVERVIEW*** THE MEDIUM RANGE PERIOD ON FRIDAY WILL BEGIN WITH A BROAD RIDGE ALOFT OVER THE EASTERN U.S., A TROUGH OVER THE NORTH-CENTRAL STATES, AND A RIDGE OVER THE WEST COAST. AN ELONGATED FRONTAL ZONE WITH MULTIPLE WAVES OF LOW PRESSURE ALONG IT IS EXPECTED ACROSS THE CENTRAL PLAINS TO THE UPPER MIDWEST, AND EXTENDING EASTWARD TO NEW ENGLAND. THE UPPER TROUGH IS FORECAST TO SLOWLY LIFT OUT INTO CANADA ALONG WITH ITS ACCOMPANYING SURFACE LOW BY SUNDAY NIGHT, WITH QUASI-ZONAL FLOW ACROSS MOST OF THE NATION TO BEGIN NEXT WEEK. A FRONT MOVING ACROSS THE PACIFIC NORTHWEST LATER IN THE FORECAST PERIOD SHOULD BE ACCOMPANIED BY AN UPPER LEVEL TROUGH BUILDING OVER SOUTHWEST CANADA. ***MODEL PREFERENCES*** FOR THE MOST PART, MODELS AND ENSEMBLES ARE IN RELATIVELY GOOD AGREEMENT AT THE BEGINNING OF THE FORECAST PERIOD WITH RESPECT TO THE UPPER LEVEL PATTERN. SIMILAR TO YESTERDAY, THE GFS REMAINS A MORE AMPLIFIED SOLUTION ACROSS THE CENTRAL U.S. WITH RESPECT TO THE TROUGH FROM SOUTHERN CANADA, AND IS ALSO HINTING AT A WEAK UPPER LOW FORMING NEAR SOUTHERN CALIFORNIA. REGARDLESS OF WHETHER THIS FEATURE DEVELOPS, THE SENSIBLE WEATHER IMPACTS WOULD BE NEGLIGIBLE. THE CMC IS FASTER IN LIFTING THE TROUGH OUT OF THE GREAT LAKES REGION SATURDAY NIGHT, WHEREAS THE ENSEMBLE MEANS ARE CLOSER TO THE GFS AND ECMWF. IN TERMS OF MODEL PREFERENCES, A BLEND OF THE OPERATIONAL UKMET, GFS, AND ECMWF WAS INCORPORATED FOR THE FIRST HALF OF THE FORECAST PERIOD. INCREASING PERCENTAGES OF THE GEFS AND EC MEANS WERE USED FOR NEXT WEEKEND WHEN UNCERTAINTIES RELATED TO MESOSCALE DETAILS BECOME MORE SIGNIFICANT. ***SENSIBLE WEATHER*** WITH THE EAST COAST RIDGE AND MIDWEST TROUGH, A COLD FRONT WILL BECOME NEARLY STATIONARY FROM THE GREAT LAKES DOWN ACROSS THE MIDWEST AND THE CENTRAL PLAINS AS THE BERMUDA HIGH BUILDS AND KEEPS THE FRONT FROM MAKING SIGNIFICANT EASTWARD PROGRESS. THIS WILL CONCENTRATE SHOWERS AND THUNDERSTORMS ALONG AND AHEAD OF THE FRONT, WITH THE POSSIBILITY OF HEAVY RAIN FROM OKLAHOMA TO THE GREAT LAKES REGION THROUGH EARLY SUNDAY. BY MONDAY AND INTO EARLY TUESDAY, SHOWERS AND THUNDERSTORMS SHOULD BECOME MORE SCATTERED IN NATURE ACROSS THE EASTERN HALF OF THE COUNTRY. THE GREATEST COVERAGE IS LIKELY ACROSS THE UPPER MIDWEST AND EXTENDING EASTWARD TO SOUTHERN MICHIGAN BASED ON THE LATEST MODEL GUIDANCE. IN TERMS OF TEMPERATURES, EXPECT HOT AND DRY CONDITIONS TO CONTINUE FOR THE LOWER ELEVATIONS OF THE SOUTHWEST, BUT NOTHING RECORD BREAKING IS CURRENTLY ANTICIPATED. AFTER A FEW DAYS OF COOLER WEATHER, EXPECT HOT AND HUMID CONDITIONS FOR MOST OF THE EAST COAST REGION IN TIME FOR THE WEEKEND. HAMRICK