ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 324 PM EDT WED JUL 12 2017 VALID 12Z SUN JUL 16 2017 - 12Z THU JUL 20 2017 ...PATTERN OVERVIEW AND MODEL ASSESSMENT/PREFERENCES... MODELS SHOW GENERALLY GOOD AGREEMENT ON THE LARGE-SCALE PATTERN ACROSS ALASKA SUN-THU (DAYS 4-8). A BLOCKING RIDGE INITIALLY ACROSS THE STATE ON DAY 3 IS FORECAST TO PROGRESS VERY SLOWLY EASTWARD. ONE LOW AMPLITUDE SHORTWAVE IS FORECAST TO MOVE NORTHWARD ACROSS WESTERN ALASKA DURING DAYS 3-4. MODELS SHOW SOME SPREAD WITH RESPECT TO THE TIMING OF THIS FEATURE (WITH THE GEM GLOBAL A BIT SLOWER THAN THE GFS/ECMWF TO MOVE THIS FEATURE NORTH INTO THE ARCTIC OCEAN. BY NEXT TUE-THU, MODEL CONSENSUS IS HIGH WITH RESPECT TO A LARGE UPPER LOW MOVING INTO THE BERING SEA. A NOTICEABLE TREND IN THE MODELS TOWARD A FASTER PROGRESSION OF THIS SYSTEM WAS NOTED COMPARED TO YESTERDAY, AND THIS IS REFLECTED IN THE WPC FORECAST. WHILE THE DETERMINISTIC SOLUTIONS SHOW SOME SPREAD WITH RESPECT TO THE EXACT EVOLUTION OF THIS FEATURE THE GEM GLOBAL REMAINS A SLOW OUTLIER WHILE THE 00Z ECMWF WAS A BIT NORTH OF THE MODEL CONSENSUS. THE GEFS/CMC/ECMWF ENSEMBLE MEANS ARE IN RELATIVELY GOOD AGREEMENT, HOWEVER. THUS, THE WPC FORECAST WAS BASED ON A 50/50 DETERMINISTIC/ENSEMBLE BLEND INITIALLY (INCLUDING THE GFS/ECMWF/GEFS/ECMWF ENS), WITH A GRADUAL TREND TOWARD HEAVIER ENSEMBLE WEIGHTING DURING THE DAY 6-8 TIME FRAME. ...WEATHER IMPACTS... THE UPPER RIDGE WILL KEEP TEMPERATURES GENERALLY ABOVE AVERAGE, PARTICULARLY ACROSS THE EASTERN HALF OF ALASKA. WHILE SCATTERED SHOWERS WILL OCCUR, POPS WILL GENERALLY BE BELOW CLIMATOLOGICAL NORMS UNTIL THE BERING SEA LOW PRESSURE SYSTEM APPROACHES WESTERN MAINLAND ALASKA BY MON-WED, WHICH SHOULD INCREASE PRECIPITATION CHANCES ACROSS THE WESTERN HALF OF THE STATE. THE ALEUTIANS WILL SEE SHOWERY AND WINDY CONDITIONS EARLY IN THE MEDIUM RANGE IN ASSOCIATION WITH THE SAME LOW PRESSURE SYSTEM. RYAN