EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1109 AM EDT FRI JUL 14 2017 VALID 12Z MON JUL 17 2017 - 12Z FRI JUL 21 2017 ...PATTERN OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES... MODELS CONTINUE TO SHOW RELATIVELY GOOD AGREEMENT ON THE LARGE SCALE FLOW PATTERN ACROSS THE CONUS INTO NEXT WEEK. A TROUGH INITIALLY ACROSS THE EASTERN U.S. ON DAY 3 (MON) IS EXPECTED TO GRADUALLY LIFT OUT THROUGH MIDWEEK. MODELS CONTINUE TO SHOW SOME MINOR DIFFERENCES WITH RESPECT TO THE SPEED THAT THIS OCCURS, BUT CONSENSUS HAS IMPROVED COMPARED TO THIS TIME YESTERDAY. CONSENSUS IS GOOD ON A BROAD UPPER LEVEL HIGH BUILDING EASTWARD INTO THE MID-MISSISSIPPI VALLEY, WITH A SURFACE FRONTAL BOUNDARY GENERALLY WEST-EAST ORIENTED ACROSS THE NORTHERN TIER ATTEMPTING TO MAKE SOME INROADS SOUTHWARD. SOME SPREAD REMAINS AS TO THE EVENTUAL POSITION OF THE UPPER RIDGE CENTER. THE ECMWF/ECMWF ENS MEAN REMAIN A BIT FARTHER EAST THAN THE GFS/GEFS, BUT THE TWO CAMPS SEEM TO HAVE CONVERGED TO SOME DEGREE RELATIVE TO YESTERDAY, WITH THE CENTRAL PLAINS OR MID-MS VALLEY REMAINING THE MOST LIKELY LOCATION BY DAY 5-7 (WED-FRI). FINALLY, SOME SPREAD EXISTS WITH RESPECT TO HOW QUICKLY AN UPPER LOW LINGERING IN THE NORTH PACIFIC THROUGH MOST OF THE MEDIUM RANGE WILL MOVE EAST INTO THE PAC NW OR BRITISH COLUMBIA LATE NEXT WEEK. THE 06Z GFS SEEMS TO WEAKEN THE WAVE MUCH MORE QUICKLY AND MOVES IT WELL EAST INTO CANADA BY FRI. THIS IS A CHANGE FROM THE FEW PREVIOUS GFS RUNS, WHICH MORE CLOSELY RESEMBLED THE 00Z ECMWF. THE 06Z GEFS/00Z ECMWF ENS MEANS ALSO SUPPORT A SLOWER PROGRESSION. THUS, THE 06Z GFS SEEMS TO BE A RELATIVELY LOW PROBABILITY SOLUTION AT THIS TIME BASED ON THE CURRENT DETERMINISTIC/ENSEMBLE SPREAD ACROSS THE PAST FEW RUNS. ...WEATHER HIGHLIGHTS... THE UPPER HIGH OVER THE CENTRAL U.S. MIDWEEK WILL SUPPRESS PRECIPITATION UNDERNEATH IT BUT ACT TO INCREASE IT TO ITS WEST AS IT DRAWS IN AND MAINTAINS WELL ABOVE AVERAGE PRECIPITABLE WATER VALUES FROM NORTHERN MEXICO THROUGH THE FOUR CORNERS REGION INTO THE LOWER COLORADO RIVER VALLEY AND GREAT BASIN. LOCALLY HEAVY RAINFALL IS POSSIBLE WITH MAINLY AFTERNOON CONVECTION MOVING OFF THE HIGH TERRAIN. TO THE NORTH OF THE UPPER HIGH AND ALONG/AHEAD OF THE FRONT, SHOWERS AND THUNDERSTORMS WILL SLIDE FROM WEST TO EAST DUE TO AFTERNOON HEATING BUT ENHANCED BY SMALLER SCALE SHORTWAVES COMING OUT OF THE NORTHERN ROCKIES. DUE TO THE SLOW PROGRESSION AND WEST TO EAST ORIENTATION OF THE FRONTAL BOUNDARY, HEAVY RAINFALL WILL BE POSSIBLE. TEMPERATURES WILL WARM AHEAD OF THE FRONT (3-8 DEG F ABOVE AVERAGE) WITH GENERALLY NEAR TO PERHAPS JUST BELOW AVERAGE TEMPERATURES TO THE NORTH ALONG THE US/CANADIAN BORDER FROM THE UPPER MIDWEST INTO NEW ENGLAND. RYAN/FRACASSO