ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 209 PM EST TUE DEC 15 2015 VALID 12Z SAT DEC 19 2015 - 12Z WED DEC 23 2015 ...MORE STORMY ALASKAN WEATHER ON TAP... ...GUIDANCE/PREDICTABILITY ASSESSMENTS... THE WPC ALASKAN MEDIUM RANGE PRODUCT SUITE HAS BEEN PRIMARILY DERIVED FROM THE 00 UTC ECMWF DAY 4/SAT THAT OFFERS SLIGHTLY BETTER WPC CONTINUITY THAN THE 12 UTC GFS...BUT MIXED IN SOME ENSEMBLE MEANS TO SMOOTH THE LESS PREDICTABLE SMALLER SCALE ROUGH EDGES. THE LATEST 12 UTC ECMWF IS QUITE COMPATABLE WITH THE SISTER 00 UTC ECMWF RUN AS WELL THIS WEEKEND. THIS LEADS INTO A COORDINATED TRANSITION DAY 5/SUN TO AN ENSEMBLE MEAN BASED FORECAST THOUGH EARLY NEXT WEEK IN A PERIOD OF GROWING FORECAST SPREAD. DETERMINISTIC MODEL RUN TO RUN VARIANCE INCREASES OVER THE PERIOD...LENDING PREFERENCE FOR THE ENSEMBLE MEAN FORECAST APPROACH. THE 06 UTC GEFS MEAN ALONG WITH THE 00 UTC ECMWF ENSEMBLE MEAN/NAEFS MEAN SOLUTIONS SEEM QUITE REASONABLE/COMPATABLE AND WELL CLUSTERED. THE OVERALL FORECAST OFFERS SLIGHTLY BELOW NORMAL UNCERTAINTY IN AN ACTIVE PATTERN WITH MORE BIG LOWS EFFECTING AK AND ADJOINING WATERS. ...FLOW PATTERN AND SENSIBLE WEATHER HIGHLIGHTS/THREATS... SUPPORT ALOFT FOR LEAD WEEKEND LOW TRANSLATION OVER THE GULF OF AK WILL GRADUALLY WANE...BUT SHOULD SUPPORT HEAVY PRECIPITATION INTO SRN AND SE AK. UPSTREAM...A VERY DEEP/ORGANIZED BERING SEA LOW WILL MEANWHILE TRANSFER POTENT ENERGIES AND WRAP HIGHLY UNSETTLED WIND/WEATHER/PRECIPITATION THROUGH SWRN AK BEFORE EMERGING OVER THE GULF OF AK LATE WEEKEND INTO EARLY NEXT WEEK. THIS WILL THREATEN SRN/SERN AK WITH LOCALLY HEAVY/TERRAIN ENHANCED PRECIPITATION. ADDITIONAL UPSTREAM LOW/FRONTOGENESIS APPROACH INTO THE ALEUTIANS/SRN BERING SEEMS ON TAP AGAIN THROUGH EARLY NEXT WEEK AS WELL IN A CONTINUING STORMY PATTERN WITH PLENTY OF FLOW WRAPPING FROM UNDERNEATH OVER THE NRN/NERN PACIFIC. COOLING/UNSETTLING NRN STREAM MEAN MID-UPPER LEVEL TROUGHING WITH MORE MODEST MOISTURE/PRECIPIATTION IS ALSO EXPECTED TO HOLD OVERTOP THROUGH THE WEEKEND INTO EARLY/MID NEXT WEEK AS PERIODICALLY REINFORCED BY DIGGING IMPULSES DOWN THROUGH NRN AK AND THE INTERIOR. SCHICHTEL