EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1139 AM EDT SAT JUN 10 2017 VALID 12Z TUE JUN 13 2017 - 12Z SAT JUN 17 2017 ...OVERVIEW/WEATHER HIGHLIGHTS... THE PATTERN STARTS OFF DURING THE MEDIUM RANGE PERIOD WITH AN AMPLIFIED UPPER TROUGH OVER THE WEST WITH A DYNAMIC LOW PRESSURE SYSTEM DEPARTING THE REGION AND A DOME OF HIGH PRESSURE ENCOMPASSING THE UPPER MS VALLEY INTO THE ERN/NERN QUAD OF THE COUNTRY, WHICH COULD DELIVER RECORD HIGHS ON MON AND TUES. BY D+8, THE NEG ANOMALY FOLLOWS THE ROBUST SYSTEM WITH TROUGHING EXTENDING ACROSS THE UPPER MIDWEST/GREAT LAKES AND POSSIBLY EXPANDING SOUTH TO THE PERSISTENT WEAKNESS NEAR THE GULF COAST/GULF OF MEXICO, THE UPPER RIDGING WILL EXIST ALONG THE EAST COAST UP INTO THE CANADIAN MARITIMES AND A SPRAWLING POSITIVE ANOMALY FROM THE EASTERN PAC INTO THE WEST WITH POTENTIAL FAST ZONAL FLOW TO THE NORTH. ...GUIDANCE/UNCERTAINTY ASSESSMENT... THE LATEST GUIDANCE HAS A SOLID HANDLING OF THE FIRST COUPLE DAYS OF THE FCST PERIOD, TUES AND WED, WHILE POSSIBLY EXPANDING INTO THURS. THE IMPRESSIVE CLOSED LOW AND SURFACE REFLECTION WILL DEPART THE NRN ROCKIES/PLAINS AND LIFT NORTH AND EAST THROUGH THE DAKOTAS INTO CENTRAL CANADA/ONTARIO, WHILE ITS TRAILING COLD FRONT TRANSITIONS THROUGH THE NRN TIER OF THE COUNTRY BUT POSSIBLY STALLS NEAR THE CENTRAL/SRN PLAINS. ALSO, DESPITE THE POSSIBLE RECORD HEAT/ON MON/TUES FOR PARTS OF THE NORTHEAST/NRN MID-ATL, A BACK DOOR COLD FRONT WILL SURGE SOUTH AND REACH THE DELMARVA BEFORE GRADUALLY ATTEMPTING TO RETURN BACK NORTH AND EAST NEXT FRI/SAT. THE ISSUES IN THE FORECAST BEGIN THURS AND CONTINUE TO FRI-SAT WITH THE NEG ANOMALY DEPARTING THE WEST AND A PATTERN TRANSITION FROM THE PAC INTO WEST AND MIDWEST. A LARGE AREA OF LOW PRESSURE SOUTH OF AK WILL TRANSITION TO THE NERN PAC/OFF THE BRITISH COLUMBIA COAST AND STEER A SERIES OF SHORT WAVE IMPULSES TOWARD BC/PAC NW. ITS THE FLATTENING OF THE JET AND THE PROGRESSION/DEPTH OF EACH SHORT WAVE FEATURE THAT WILL BE DIFFICULT TO TRACK AND HOW EXACTLY IT IMPACTS THE OVERALL LARGE/SYNOPTIC SCALE PATTERN. WPC STARTED OFF WITH 70-80 PERCENT OPERATIONAL GFS/ECMWF FOR TUES AND WED AND TRANSITION TO 70 PERCENT GEFS/EC MEAN AND NAEFS BLEND BY NEXT FRI AND SAT. ...WEATHER HIGHLIGHTS... WITH CONFIDENCE IN THE FORECAST ON TUES, EXPECT LOCALLY HEAVY QPF OVER WRN MT, ACROSS PARTS OF THE UPPER MIDWEST/MS VALLEY WITH POSSIBLY SOME RECORD HIGHS IN THE NRN MID-ATL STATES NEAR THE MAJOR METRO CITIES FROM RIC UP TO DC TO PHL. THE REST OF THE FORECAST, EXPECT AN UNSETTLED ERN THIRD TO TWO-THIRDS OF THE COUNTRY WITH CONVECTION AND HEAVY RAIN POTENTIAL AHEAD AND ALONG THE PROGGED SURFACE COLD FRONT AND AROUND THE LARGE BERMUDA HIGH. A MEAN TO HIGH TEMPS OVER THE PERIOD, SUGGEST ABOVE AVG HIGHS FROM CA/DESERT SW TO MUCH OF THE PLAINS ALONG WITH THE MID TO UPPER MS VALLEY INTO THE OH VALLEY/MID-ATL REGION. MEANWHILE BELOW AVG HIGHS WILL BE POSSIBLE ON AVG ACROSS FL, COASTAL NORTHEAST/NEW ENGLAND AND PARTS OF THE PAC NW/NRN ROCKIES TO NRN PLAINS. MUSHER