EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1215 PM EDT FRI JUN 12 2015 VALID 12Z MON JUN 15 2015 - 12Z FRI JUN 19 2015 *** A HEAVY CONVECTIVE RAIN THREAT IS POSSIBLE FROM THE WRN GULF COAST THROUGH THE PLAINS AND ACROSS THE MID-UPPER MS VALLEY/MIDWEST/OH VALLEY AND INTO THE MID-ATLANTIC*** *** TEMPERATURES COULD APPROACH RECORD HIGHS OVER GEORGIA AND THE CAROLINAS *** ...PATTERN OVERVIEW... SUBTROPICAL RIDGING EXPANDING OVER THE SOUTHERN TIER OF THE NATION EARLY NEXT WEEK WILL KEEP FRONTAL SYSTEMS CROSSING THE NORTHERN U.S. FROM PRESSING INTO THE LOWER LATITUDES...RESULTING IN A STALLED FRONTAL BOUNDARY EXTENDING FROM THE CENTRAL PLAINS TO THE NORTHERN MID-ATLANTIC COAST. A CLOSED LOW OFF THE BRITISH COLUMBIA COAST SHOULD BEGIN TO SINK SOUTH TOWARDS THE MIDDLE OF NEXT WEEK AND COULD EVENTUALLY LEAD TO MEAN TROUGHING OVER THE WESTERN U.S. BY LATE NEXT WEEK. ...MODEL EVALUATION AND PREFERENCES... DETERMINISTIC GUIDANCE HAS COME INTO GOOD AGREEMENT WITH THE MEAN FLOW OVER THE CONUS THROUGH THE MIDDLE OF NEXT WEEK...BUT THE DETAILS OF THE FORECAST BECOME VERY UNCERTAIN BY NEXT THURSDAY AND FRIDAY. MODELS ARE STILL SHOWING VARYING SOLUTIONS WITH WHERE A POSSIBLE BREAK IN THE SUBTROPICAL RIDGE SETS UP OVER TEXAS...AND ARE ALSO DIVERGING WITH THE EVOLUTION OF THE CLOSED LOW SINKING SOUTH FROM THE BRITISH COLUMBIA COAST. THE WPC FORECAST RELIED ON A BLEND OF THE AGREEABLE 00Z GFS/ECMWF FOR THE DAY 3-4 FORECAST...BUT THEN TRANSITIONED TO ENSEMBLE MEAN GUIDANCE BY DAY 5 IN ORDER TO ACCOUNT FOR THE UNCERTAINTY. ...SENSIBLE WEATHER HIGHLIGHTS/THREATS... THE WESTERN GULF COAST AND INLAND ACROSS PORTIONS OF THE PLAINS AND MID-UPPER MISSISSIPPI VALLEY WILL REMAIN VULNERABLE TO HEAVY RAINS EARLY NEXT WEEK AS ANOMALOUS MOISTURE CONTINUES TO GETS PULLED NORTHWARD OUT OF THE GULF AND AROUND THE WESTERN SIDE OF THE RIDGE EXPANDING OVER THE SOUTHEAST. DEPENDING ON THE TRACK/DEPTH OF ANY SURFACE WAVES AND PERIODIC EPISODES OF CONVECTION DEVELOPING NEAR LINGERING BOUNDARIES STALLING OVER THE NRN PERIPHERY OF THE RIDGE...THE MIDWEST/GREAT LAKES...NORTHEAST...AND NRN MID-ATLANTIC STATES COULD ALSO SEE HEAVY RAINS. BENEATH THE MAIN RIDGE ALOFT...TEMPERATURES COULD APPROACH RECORD HIGHS ACROSS GEORGIA AND THE CAROLINAS. GERHARDT