ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 239 PM EDT FRI APR 15 2016 VALID 12Z TUE APR 19 2016 - 12Z SAT APR 23 2016 ...GUIDANCE/UNCERTAINTY ASSESSMENTS... TODAYS ALASKAN MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A COMPOSITE BLEND OF COMPATABLE AND SEEMINGLY REASONABLE GUIDANCE FROM THE 12 UTC GFS...06 UTC GEFS MEAN...00 UTC ECMWF...AND 00 UTC NAEFS/ECMWF ENSEMBLES TUE-WED. OPTED TO THEN USE MORE OF JUST AN ENSEMBLE FORECAST METHODOLOGY THROUGH LATER NEXT WEEK AMID INCREASED BUT MANAGEABLE FORECAST SPREAD AT THESE LONGER TIME FRAMES...BUT DID INCLUDE A SMALL INPUT FROM THE 12 UTC GFS THAT OF THE DETERMINISTIC GUIDANCE SEEMED MOST IN LINE WITH THESE ENSEMBLES. THIS FORECAST SCENARIO WAS COORDINATED BETWEEN WPC AND ANCHORAGE AND JUNEAU NWS FORECAST OFFICES. FORECAST PREDICTABILITY IS AT OR ABOVE AVERAGE. ...PATTERN HIGHLIGHTS/THREATS... IT REMAINS EVIDENT THAT A MAIN WIND/WAVE THEN INLAND HEAVY PCPN THREAT SHOULD BE FROM THE PACIFIC INTO THE ALEUTIANS AND SW AK IN MOISTENING LEAD FLOW AHEAD AND AROUND A SERIES OF SIGNIFICANT LOWS EXPECTED TO TRACK GENERALLY ALONG/SOUTH OF THE ALEUTIANS AS POWERED BY AMPLE JET ENERGY/TRIPLE POINT LOW DEVELOPMENTS. APPLIED MANUAL FORECASTER ADJUSTMENTS TO THE BASE WPC COMPOSITE GUIDANCE BLENDS TO INSURE SUFFICIENTLY DEEP OFFSHORE LOWS CONSISTENT WITH DYNAMIC SUPPORT. SOME STORM ENERGIES ALSO GRADUALLY SPREAD DOWNSTREAM OVER THE GULF OF AK AND SERN AK NEXT WEEK...WORKING INTO AN AMPLIFIED DOWNSTREAM MEAN MID-UPPER RIDGE POSITION IN PLACE FROM WRN CAN NWWD TOWARD THE ALASKAN INTERIOR. OVERTOP...MODEST MID-UPPER LEVEL TROUGHING FROM NEAR THE BERING STRAIT/CHIKCHI SEA TO NWRN AK INTO TUE MAY SUPPORT SOME LINGERING SNOWS. SCHICHTEL