EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 250 AM EDT FRI JUL 08 2016 VALID 12Z MON JUL 11 2016 - 12Z FRI JUL 15 2016 ...PATTERN OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENT... A HIGH AMPLITUDE PATTERN WILL BE IN PLACE TO COMMENCE THE MEDIUM RANGE PERIOD AS LARGE-SCALE HEIGHT FALLS ADVANCE THROUGH THE CENTRAL/NORTHERN HIGH PLAINS EARLY MONDAY. IN ADVANCE OF THIS AMPLIFIED SYSTEM...A SPLIT FLOW REGIME IS EXPECTED AS AN UPPER TROUGH EXITS NOVA SCOTIA WHILE A WEAK SHORTWAVE MEANDERS ABOUT THE MID-SOUTH REGION. FOCUSING ON THE LATTER FEATURE...THE 12Z ECMWF/CMC HANDLE THE TIMING SIMILARLY WHILE THE RECENT GFS RUNS CONTINUE TO BE SLOWER WHILE DRAGGING THE ENERGY UP INTO THE OH RIVER VALLEY BY TUESDAY MORNING. ELSEWHERE...THERE IS SUFFICIENT AGREEMENT AMONG THE RECENT GUIDANCE TO SUPPORT A STRONG AREA OF LOW PRESSURE IN THE VICINITY OF EXTREME SOUTHERN SASKATCHEWAN OR JUST SOUTH OF THE INTERNATIONAL BORDER INTO WESTERN ND. THIS SLOW MOVING SYSTEM SHOULD GRADUALLY GATHER SPEED AS IT EVOLVES INTO MORE AN OPEN WAVE ACROSS THE UPPER MIDWEST BY THURSDAY MORNING. RELATIVE TO THE 12Z GUIDANCE SUITE...00Z MODELS WHICH ARRIVED AFTER THE WPC FRONTS/PRESSURES PACKAGE HAVE TRENDED QUICKER...PARTICULARLY THE 00Z UKMET. THESE LOWER HEIGHTS ARE FORECAST TO EVENTUALLY REACH THE GREAT LAKES REGION AND INTO THE INTERIOR NORTHEAST BY THE END OF THE PERIOD WITH THE ACCOMPANYING FRONTAL ZONE BECOMING NEARLY STATIONARY OVER THE OH VALLEY/LOWER GREAT LAKES. LOOKING FARTHER UPSTREAM...THERE ARE SOME COMPLEXITIES WITHIN THE BLOCKING REGIME OVER THE NORTHEASTERN PACIFIC. WHILE THE POWERFUL INITIAL UPPER LOW SWINGS THROUGH THE NORTHERN TIER STATES...AN ADDITIONAL CLOSED SYSTEM SINKS SOUTHEASTWARD TOWARD VANCOUVER ISLAND. THE MODELS SHOWED QUITE A BIT OF VARIATION IN WHAT TO DO WITH THIS SYSTEM...MAINLY WITH TIMING. RECENT 00Z TRENDS SHOW MORE RETROGRESSION THAN THE 12Z ECMWF/UKMET HAD BEEN ADVERTISING. SUCH FORECASTS FAVORED A CLOSED LOW WHICH WOULD SLOWLY MOVE TOWARD SOUTHWESTERN BRITISH COLUMBIA BY LATE IN THE WORK WEEK. IN CONTRAST...RECENT GFS RUNS HAVE SHOWED A LARGER SEPARATION AS THE CORE OF THE UPPER LOW WOULD STALL AND RETROGRADE DURING THE PERIOD. THE OVERALL BASIS OF THE FORECAST WAS TO LEAN MORE IN THE DIRECTION OF THE 12Z ECMWF/ECMWF ENSEMBLE MEAN...PARTICULARLY LATER IN THE PERIOD AS THE UNCERTAINTY OF THE UPSTREAM FEATURES CAME INTO PLAY. THROUGH DAY 5...FELT CONFIDENT ENOUGH IN THE DEEP SOLUTIONS AMONG THE 18Z GFS AND 12Z ECMWF/UKMET TO INCORPORATE THEIR SURFACE PRESSURES INTO THE MIX. DID MOVE IN THE DIRECTION OF THE ENSEMBLE MEANS THEREAFTER WITH MORE EMPHASIS ON THE 12Z ECMWF ENSEMBLE MEAN. GIVEN THE 00Z MODEL TRENDS...SOME ADJUSTMENTS MAY BE NECESSARY WITH THE MORNING MEDIUM RANGE PACKAGE. ...WEATHER HIGHLIGHTS/THREATS... IN THE WAKE OF THE STRONG UPPER CYCLONE ADVANCING INTO SOUTH-CENTRAL CANADA...MUCH COOLER WEATHER WILL PREVAIL AS FORECAST TEMPERATURE ANOMALIES REACH THE 10 TO 15 DEGREE BELOW AVERAGE RANGE THROUGH TUESDAY. THIS WILL PARTICULARLY BE THE CASE ON MONDAY FROM THE CENTRAL GREAT BASIN UP INTO THE NORTHERN ROCKIES/HIGH PLAINS WHERE HIGHS WILL ONLY BE IN THE 60S TO LOWER 70S. OVER THE REMAINDER OF THE U.S...TEMPERATURES SHOULD BE AROUND NORMAL TO ABOVE AVERAGE FOR THE MOST PART. ONE OF THE WARM SPOTS WILL BE OVER THE SOUTHERN HIGH PLAINS WITH HIGHS NEARING OR EXCEEDING THE CENTURY MARK EACH DAY. REGARDING PRECIPITATION AND SEVERE WEATHER POTENTIAL...THE STORM PREDICTION CENTER CONTINUES TO ADVERTISE AN OUTLOOK FROM THE DAKOTAS INTO THE UPPER MIDWEST AHEAD OF THE POWERFUL UPPER LOW/ASSOCIATED COLD FRONT. HEAVY RAINFALL IS ALSO LIKELY WITHIN THE COMMA-HEAD OF THE DEEP AREA OF LOW PRESSURE. ADDITIONAL LOCALIZED HEAVY RAINFALL IS POSSIBLE ALONG THE COLD FRONT ITSELF AS WELL AS ALONG THE LIFTING WARM FRONTAL ZONE. RUBIN-OSTER