ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 228 PM EDT THU JUL 23 2015 VALID 12Z MON JUL 27 2015 - 12Z FRI JUL 31 2015 STRETCH OF ABOVE AVERAGE PREDICTABILITY CONTINUES IN THE HIGH LATITUDES... WITH A GENERAL RETROGRESSION OF AN UPPER LOW ACROSS THE ARCTIC OCEAN AND A CONTINUED EASTWARD 'PROGRESSIVENESS' OF THE FLOW PATTERN ACROSS THE NORTH CENTRAL PACIFIC AND DOWNSTREAM INTO WEST CENTRAL NORTH AMERICA. A BLEND OF THE 23/00Z ECENS---ITS OPERATIONAL RUN AND THE 23/06Z GEFS MEANS MAINTAINED DECENT CONTINUITY INTO DAY 6 (29/12Z) AT THE SURFACE AND ALOFT. THE OPERATIONAL ECMWF BEGAN TO DEVIATE SIGNIFICANTLY FROM ITS MEAN AFTER 29/12Z AND WENT WITH A 70/30 RATIO OF THE ECENS/GEFS BY 30/00Z. THE OPERATIONAL ECMWF IS A SIGNIFICANTLY DEEPER SOLUTION NEAR THE SURFACE BEYOND DAY 5 WITH ITS INTRODUCTION OF 'HALOLA' INTO THE WESTERLIES---AND BETTER TO 'WAIT OUT' THIS PARTICULAR TROPICAL INTRUSION. BASED UPON THE TRACK RECORD OF PREVIOUS SYSTEMS (RECENT ONES) --- 'CHAN-HOM' AND 'NANGKA' ---THE DETERMINISTIC GUIDANCE HAVE BEEN POORLY-PERFORMING PRODUCTS---AT/BEYOND THE DAY 4-5 POINT. AND BELIEVE 'HALOLA' HAS BEEN CAST 'A SIMILAR FATE'. VOJTESAK