ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 242 PM EDT SUN SEP 24 2017 VALID 12Z THU SEP 28 2017 - 12Z MON OCT 02 2017 ENSEMBLE MEANS CONTINUE TO BE IN VERY GOOD AGREEMENT WITH THE LONGWAVE PATTERN OVER ALASKA DURING THE LATER HALF OF THE WEEK, WHICH SHOULD FEATURE AN ANOMALOUS UPPER LOW LIFTING NORTHEASTWARD THROUGH THE GULF OF ALASKA WHILE UPSTREAM RIDGING PROGRESSES THROUGH THE BERING SEA. THE MEANS MAINTAIN AGREEMENT EVEN INTO NEXT WEEKEND AND EARLY NEXT WEEK WITH ADVERTISING RIDGING IN BERING SEA SHOULD SUPPRESS AND SHIFT EASTWARD AS A LARGE SCALE UPPER TROUGH APPROACHES FROM THE WEST. THE WPC FORECAST STARTED WITH A BLEND OF THE 00Z GFS/ECMWF/ENSEMBLE MEANS, WHICH ACCOUNTED FOR THE REASONABLE AGREEMENT AMONG DETERMINISTIC GUIDANCE EARLY IN THE PERIOD WHILE ALSO SMOOTHING OUT SOME OF THE LINGERING DETAIL DIFFERENCES WITH A STRONG SURFACE LOW AND COLD FRONT LIFTING THROUGH THE GULF AND INTO THE SOUTHERN COAST ON THURSDAY. BY DAY 6(SATURDAY), ENSEMBLE SPREAD AND UNCERTAINTY QUICKLY INCREASES WITH THE EVOLUTION OF THE UPPER LOW IN THE GULF AS WELL AS WITH THE TIMING OF THE LEADING EDGE OF HEIGHT FALLS FROM THE LARGE SCALE UPPER TROUGH EDGING INTO THE BERING SEA, SO THE WPC FORECAST TRANSITIONED TO PREDOMINANTLY ENSEMBLE MEANS (00Z GEFS/NAEFS/EC MEAN) FOR THE DAY 6-8(SATURDAY-MONDAY) FORECAST. IN TERMS OF SENSIBLE WEATHER OVER ALASKA DURING THE DAY 4-8 PERIOD, MODELS CONTINUE TO SHOW A STRONG SIGNAL THAT A PERSISTENT STREAM OF MOISTURE AHEAD OF THE DEEP SURFACE LOW AND COLD FRONT LIFTING THROUGH THE GULF WILL BRING HEAVY PRECIPITATION TO THE PANHANDLE DURING THE MIDDLE OF THE WEEK, WITH THE WET CONDITIONS EXPECTED TO SPREAD INTO THE SOUTHCENTRAL PORTION OF THE STATE. ALSO, STRONG WINDS AND AN INCREASED CHANCE OF PRECIPITATION WILL BE POSSIBLE WITH HEIGHT FALLS EDGING INTO THE BERING SEA AND WESTERN/CENTRAL ALEUTIANS NEXT WEEKEND. GERHARDT