ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 213 PM EDT TUE SEP 27 2016 VALID 12Z SAT OCT 01 2016 - 12Z WED OCT 05 2016 A MODESTLY POSITIVE MID-LEVEL HEIGHT ANOMALY IS EXPECTED TO PREVAIL OVER THE ALASKA MAINLAND DAYS 4-8 WHILE COMPENSATING NEGATIVE MID LEVEL HEIGHT ANOMALIES DEVELOP OVER RUSSIA AND BRITISH COLUMBIA. THE MAIN IMPACTS OF THIS PATTERN ARE GENERALLY ABOVE NORMAL TEMPERATURES AND DRY CONDITIONS FOR THE MAINLAND WITH MORE SEASONABLE TEMPERATURES AND PRECIPITATION ELSEWHERE...WHILE THE PRIMARY SYSTEM TO MONITOR WILL BE A SURFACE LOW AND ACCOMPANYING PRESSURE GRADIENT THAT ARE LIKELY TO AFFECT THE WESTERN AND CENTRAL ALEUTIANS WITH STRONG WINDS/HIGH SEAS/HEAVY RAIN DAY 4/SAT. CONFIDENCE IN THE LOW AFFECTING THE ALEUTIANS AS DEPICTED BY CURRENT GUIDANCE IN AROUND 70 PERCENT...WITH THE 00Z ECMWF MOST CONSISTENT FROM RUN-TO-RUN AND WITH ITS HIGHER SPATIAL RESOLUTION AND MORE SOPHISTICATED INITIALIZATION FAVORED OVER THE COARSER-GRIDDED AND FASTER/WEAKER 00-06-12Z GFS. BY DAY 5/SUN...MODELS DIVERGE QUICKLY AS THE LOW ENCOUNTERS THE BLOCK OVER THE MAINLAND AND SPLITS. HAVE THEREFORE MOVED QUICKLY TOWARD THE ENSEMBLE MEANS WITH MODEL BLENDING USING A NEARLY EQUAL DISTRIBUTION OF THE ENSEMBLE SYSTEMS THAT GENERALLY AGREE ON THE RIDGE PORTION OF THE BLOCK CONTINUING OR SPREADING NORTHWARD FROM THE MAINLAND ALONG WITH AN UPPER TROUGH CONTINUING OVER THE BERING SEA. CONFIDENCE ON THE DAY-TO-DAY DETAILS FALLS BELOW AVERAGE BY SUNDAY GIVEN THE GROWING SPREAD. JAMES