EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 146 AM EDT THU SEP 28 2017 VALID 12Z SUN OCT 01 2017 - 12Z THU OCT 05 2017 ...OVERVIEW... UPPER RIDGING IS FORECAST TO YET AGAIN BUILD INTO THE EASTERN HALF OF THE COUNTRY NEXT WEEK AS TROUGHING DIGS INTO THE WEST. A SURFACE COLD FRONT WILL MOVE ACROSS THE PLAINS AND SOUTHWARD THROUGH THE INTERIOR WEST BUT THEN LIFT INTO SOUTHERN CANADA AND BECOME STATIONARY BACK INTO THE CENTRAL ROCKIES. THIS WILL SET UP A RATHER COOL/WET WEST AND WARM/DRY EAST. ...GUIDANCE EVALUATION/PREFERENCES... MODELS MAY FINALLY BE SHOWING SOME CONVERGENCE ON A COMMON IDEA OF THE PATTERN OUT OF THE PACIFIC WHICH WILL DICTATE HOW THE TROUGH IN THE WEST EVOLVES. THE RIDGE IN THE EAST HAS BETTER ONGOING AGREEMENT. RELIED MOSTLY ON THE ECMWF AND ITS ENSEMBLE MEAN AS THAT ENSEMBLE SYSTEM HAS HAD MUCH BETTER CONTINUITY AND TYPICALLY HANDLES AMPLIFIED PATTERNS BETTER THAN THE GEFS ENSEMBLES. THIS HAS SUPPORT FROM THE 12Z UKMET AND ALSO THE CANADIAN (ASIDE FROM ITS LIKELY OVERDONE SFC LOW IN THE GULF OF MEXICO). THE 12Z/18Z GFS RUNS WERE CLOSER TO THE ECMWF THAN EARLIER RUNS BUT STILL SEEMED TO MISMANAGE THE PACIFIC FLOW BASED ON THE ECMWF/CANADIAN ENSEMBLES. GEFS ENSEMBLE MEMBERS SHOWED SOME OVERLAP WITH THE ECMWF MEMBERS WHICH ADDED TO THE CONSENSUS. DETERMINISTIC ECMWF MAY STILL BE OVERDONE WITH ITS LITERAL FORECAST BY THE END OF THE PERIOD WHEN IT DRIFTED TOWARD THE EDGE OF THE ENSEMBLE SPREAD. ...WEATHER HIGHLIGHTS... PRECIPITATION WILL FOCUS ACROSS FLORIDA STATIONARY FRONT THAT SHOULD EVENTUALLY DISSIPATE BY EARLY NEXT WEEK. EASTERLY FLOW AND ABOVE AVERAGE PRECIPITABLE WATER VALUES SUPPORTS RAINS WITH LOCALLY HEAVY AMOUNTS. THE WEST WILL SEE BOUTS OF RAIN AND MOUNTAIN SNOW AS EACH UPPER/SFC SYSTEM PASSES THROUGH WITH ADDITIONAL RAIN FARTHER EAST OVER THE NORTHERN PLAINS INTO THE UPPER MIDWEST AS THE LEAD FRONT MOVES SLOWLY EASTWARD AND THEN NORTHEASTWARD INTO SOUTHERN CANADA. A DRY PERIOD IS EXPECTED UNDER THE DEVELOPING UPPER HIGH IN THE OH VALLEY/TN VALLEY/INTERIOR SOUTHEAST. TEMPERATURES ABOUT 10-20 DEGREES BELOW AVERAGE WILL DEVELOP AND PERSIST ACROSS THE PACIFIC NORTHWEST/NORTHERN ROCKIES/NORTHERN HIGH PLAINS DUE TO LOWER HEIGHTS. CONTRARY TO THE WEST, THE BUILDING UPPER AND SFC HIGH IN THE OH/TN VALLEY WILL SUPPORT RISING TEMPERATURES BACK TO AND THEN ABOUT 10-15 DEGREES HIGHER THAN AVERAGE. THIS WILL SPREAD EASTWARD TOWARD THE EAST COAST BY MIDWEEK WHERE 70S AND 80S WILL RETURN. FRACASSO