ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 230 PM EDT WED AUG 30 2017 VALID 12Z SUN SEP 03 2017 - 12Z THU SEP 07 2017 ...MAJOR LOWS INTO NEXT WEEK... OVERALL...GUIDANCE SHOWS AN AMPLIFIED AND STORMY WEATHER PATTERN FOR AK. A STRONG RIDGE BUILDS OVER THE AK PANHANDLE TO THE INTERIOR AS A DEEP WRN GULF OF AK CLOSED LOW DIGS UNDERNEATH NEAR 160W. THIS OCCURS WITH APPROACH OF A POTENT EXTRATROPICAL SURFACE LOW ASSOCIATED WITH CURRENT WPAC TROPICAL STORM SANVU. A COMPOSITE BLEND OF THE 12 UTC GFS AND 00 UTC ECMWF/GEFS ENSEMBLES OFFERS MAX WPC CONTINUITY AND SHOWS AMPLE AMPLITUDE. LEANED INCREASINGLY MORE ON THE ENSEMBLE MEAN DAYS 6-8 AMID MODESTLY GROWING FORECAST SPREAD/UNCERTAINTY AND APPLIED MANUAL ADJUSTMENTS TO INSURE DEEP LOW CONSISTENT WITH SUPPORT ALOFT. MODELS ARE NOW IN BETTER AGREEMENT WITH DEVELOPMENT OF A VERY DEEP SURFACE LOW DOWN TO THE SOUTH OF THE ALEUTIANS THIS WEEKEND THAT LINGERS INTO EARLY-MID NEXT WEEK BEFORE EJECTION ACROSS THE GULF OF AK AS A DEEP EXTRATROPICAL LOW ASSOCIATED WITH CURRENT TROPICAL STORM SANVU WORKS INTO THE ALEUTIANS. EXPECT QUITE UNSETTLED CONDITIONS INTO NEXT WEEK FOR SW/SRN AK. A STRONG FETCH OF SOUTHERLY FLOW WILL DEVELOP TO DEEPEN LEAD MOISTURE INFLUX TO FUEL HEAVY RAINFALL. GUIDANCE HAS TRENDED LESS PROGRESSIVE AND DEEPER WITH THIS SYSTEM OVER THE LAST COUPLE OF DAYS AND THAT SEEMS CONSISTENT WITH FLOW AMPLIFICATION THAT OFTEN OCCURS DOWNSTREAM OF A DEEP SYSTEM OF TROPICAL ORIGIN. UPSTREAM... THE POWERFUL REMNANTS OF SANVU WILL SIGNIFICNATLY IMPACT THE SRN BERING SEA...ALEUTIANS...THEN SWRN AK WITH STRONG WINDS AND HEAVY RAINFALL DAYS 6-8. MEANWHILE...GUIDANCE OFFERS A BIT MORE SPREAD BUT NOW IS IN BETTER AGREEMENT IN SHOWING THAT A CLOSED TROUGH/LOW ALONG THE ARCTIC COAST OF RUSSIA WILL TRACK STEADILY EASTWARD TOWARD THE CHUKCHI SEA DAYS 4-6 BEFORE AN EXPECTED LIFTING OVER THE ARCTIC. AN ASSOCIATED SURFACE SYSTEM PRODUCES UNSETTLED CONDITIONS. SCHICHTEL