EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 219 AM EDT TUE SEP 20 2016 VALID 12Z FRI SEP 23 2016 - 12Z TUE SEP 27 2016 ...OVERVIEW... A COLD FRONT WILL SLOWLY MOVE OUT OF THE ROCKIES AND THROUGH THE GREAT PLAINS LATER THIS WEEK AND INTO THE WEEKEND AS A BACKDOOR COLD FRONT DIPS THROUGH THE MID-ATLANTIC AND INTO THE SOUTHEAST. AT THE UPPER LEVELS, AN UPPER LOW WILL STRETCH INTO TWO LOWS ON SUNDAY -- ONE REMAINING PROGRESSIVE BUT WEAKENING IN THE UPPER MIDWEST AND GREAT LAKES WHILE THE OTHER ONE MEANDERS IN THE FOUR CORNERS REGION. ...GUIDANCE EVALUATION AND PREFERENCES... MODELS AND ENSEMBLES CONTINUE TO STRUGGLE WITH THE DETAILS OF A SOMEWHAT COMPLICATED PATTERN EVOLUTION NEXT SUN-TUE OVER THE LOWER 48. AFTER A DEEP UPPER LOW SWINGS THROUGH THE CENTRAL ROCKIES ON SATURDAY, THE ENSEMBLES HAVE BEEN TRENDING TOWARD A MORE SEPARATED/STRETCHED UPPER PATTERN SW TO NE FROM THE GREAT BASIN TO THE HIGH PLAINS. THIS WOULD GO BACK TO THE IDEA OF A MORE PROGRESSIVE NORTHERN STREAM ALONG THE US/CANADIAN BORDER BUT A STUCK/STALLED PATTERN IN THE LOWER LATITUDES (30-35N) FROM THE SW TO THE SE. GIVEN THE CHANGES IN RECENT ENSEMBLE MEAN/MEMBER POSITIONS OF ESPECIALLY THE SOUTHERN STREAM UPPER LOW -- TRENDING FARTHER WEST OVER THE PAST FOUR CYCLES -- AND THE RELATIVE AGREEMENT BETWEEN THE RECENT 18Z GFS/GEFS AND 12Z ECMWF/ECENS MEAN, A CONSENSUS BLEND WAS SUFFICIENT THROUGH ABOUT NEXT MONDAY. BY NEXT TUESDAY, THE GFS CLUSTERED BETTER WITH THE ENSEMBLE MEANS COMPARED TO THE ECMWF, SO USED THAT BROAD CONSENSUS BY THEN BUT WITH LIMITED CONFIDENCE. ...WEATHER HIGHLIGHTS/THREATS... THE SLOWLY MOVING FRONT WILL PROVIDE A FOCUS FOR PRECIPITATION, POSSIBLY MODERATE TO HEAVY AMOUNTS, OVER THE SOUTHERN PLAINS WITH LIGHTER AMOUNTS TO THE NORTH/NORTHEAST NEAR THE WEAKENING SURFACE LOW PRESSURE. AS THE SOUTHERN UPPER LOW MEANDERS IN THE SW AND THE UPPER RIDGE STAYS PUT IN THE SOUTHEAST, SOUTHERLY FLOW WILL HELP MAINTAIN AN AXIS OF ABOVE AVERAGE PW VALUES FROM TEXAS NORTHWARD THEN NORTHEASTWARD ALONG THE FRONT. PERSISTENT FLOW ATOP THE BOUNDARY MAY SET THE STAGE FOR LOCALLY HEAVY RAIN IN THE LONE STAR STATE THIS WEEKEND INTO EARLY NEXT WEEK SHOULD THE UPPER PATTERN REMAIN LARGELY UNCHANGED FOR SEVERAL DAYS. COOLER THAN AVERAGE TEMPERATURES WILL SLOWLY EASE IN TIME OVER THE INTERIOR WEST AS RIDGING ATTEMPTS TO BUILD IN FROM THE EASTERN PACIFIC. FARTHER EAST, THE COLD FRONT WILL PUSH SOUTHWARD ALONG THE EAST COAST, BRINGING IN COOLER TEMPERATURES NEAR TO SLIGHTLY BELOW AVERAGE AFTER A LONG STRETCH OF ABOVE AVERAGE TEMPERATURES. THE SOUTHEAST WILL REMAIN WARMER THAN AVERAGE THANKS TO THE UPPER RIDGE IN PLACE. FRACASSO