EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1209 PM EDT THU JUN 11 2015 VALID 12Z SUN JUN 14 2015 - 12Z THU JUN 18 2015 *** HEAVY RAINS POSSIBLE ALONG THE NORTH/NORTHWEST GULF COAST AND ACROSS PORTIONS OF THE SOUTHERN PLAINS AND MIDDLE TO UPPER MISSISSIPPI VALLEY *** ...PATTERN OVERVIEW... ANOMALOUSLY STRONG RIDGING OVER SOUTHWEST ALASKA WILL DOMINATE THE MID-LEVEL FLOW ACROSS THE CONUS STARTING THIS WEEKEND AND CONTINUING THROUGH NEXT WEEK. SUBTROPICAL RIDGING ALONG 30N WILL STRENGTHEN IN TIME ON EITHER SIDE OF MEXICO AND EVENTUALLY OVERTAKE THE LOWER LATITUDES...FORCING THE MAIN STORM TRACK NORTH THROUGH SOUTHERN CANADA AND STALLING ATTENDANT FRONTAL BOUNDARIES OVER THE CENTRAL PLAINS...MIDWEST...AND NORTHEAST/NORTHERN MID-ATLANTIC STATES. ...MODEL EVALUATION AND PREFERENCES... MODELS ARE IN GOOD AGREEMENT WITH THE LARGE SCALE FLOW OVER THE CONUS...BUT ARE STILL SHOWING VARIATIONS WITH SOME IMPORTANT SMALLER SCALE DETAIL DIFFERENCES. ONE MAJOR CONCERN WILL BE WHERE THE BREAK IN THE SUBTROPICAL RIDGE OCCURS IN THE LOWER LATITUDES...WHICH WILL IMPACT WHERE THE HEAVIEST RAINFALL AXIS SETS UP OVER THE SOUTH CENTRAL U.S.. IN GENERAL...THE ECMWF HAS BEEN ON THE WESTERN EDGE OF MODEL SPREAD...WHILE THE GFS HAS STAYED FARTHER EAST WITH THE BREAK. A SECONDARY CONCERN IS HOW THE MODELS HANDLE INDIVIDUAL SURFACE WAVES DEVELOPING ALONG FRONTAL BOUNDARIES STALLING FROM THE NORTHERN MID-ATLANTIC STATES TO CENTRAL PLAINS. THE TRACK/DEPTH OF THESES WAVES WILL PLAY A ROLE IN TRIGGERING PRECIP ACROSS THE GREAT LAKES...OHIO VALLEY...NORTHEAST...AND NORTHERN MID-ATLANTIC STATES. THE GFS HAS TENDED TO BE ON THE WEAKER SIDE OF GUIDANCE WITH THESE WAVES...WHILE THE CMC SEEMS TO OFFER MORE AGGRESSIVE SOLUTIONS...WITH THE 00Z CMC SUGGESTING A WELL DEVELOPED SURFACE LOW TRACKING THROUGH THE NORTHEAST LATE NEXT WEEK. GIVEN THE AMOUNT OF UNCERTAINTY IN THE DETERMINISTIC GUIDANCE AND INDIVIDUAL ENSEMBLE MEMBERS FOR SOME OF THE SMALLER SCALE BUT IMPORTANT DIFFERENCES...THE WPC FORECAST STARTED WITH A CONSERVATIVE BLEND OF THE 00Z ECMWF/ECMWF ENSEMBLE MEAN AND 06Z GFS/GEFS MEAN...WHICH STRAYED LITTLE FROM CONTINUITY. ...SENSIBLE WEATHER HIGHLIGHTS... LOCATIONS ALONG THE NORTH/NORTHWEST GULF COAST AND ACROSS PORTIONS OF THE SOUTHERN PLAINS AND MIDDLE TO UPPER MISSISSIPPI VALLEY WILL BECOME VULNERABLE TO HEAVY RAINS AS ANOMALOUS MOISTURE GETS PULLED NORTHWARD OUT OF THE GULF AND AROUND THE WESTERN SIDE OF THE RIDGE EXPANDING OVER THE SOUTHEAST. DEPENDING ON THE EXACT TRACK/DEPTH OF SURFACE WAVES DEVELOPING ON A LINGERING BOUNDARY STALLING OVER THE NORTHERN PERIPHERY OF THE RIDGE...THE GREAT LAKES...NORTHEAST...AND NORTHERN MID-ATLANTIC STATES COULD ALSO SEE HEAVY RAINS. TEMPERATURES TO THE SOUTH OF THE STALLED BOUNDARY MAY APPROACH THE 100 DEGREE MARK FOR MULTIPLE DAYS IN PARTS OF GEORGIA AND SOUTH CAROLINA...WHICH WOULD BE CLOSE TO RECORD HIGH VALUES. GERHARDT