ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 237 PM EST THU FEB 16 2017 VALID 12Z MON FEB 20 2017 - 12Z FRI FEB 24 2017 RECENT MODELS AND ENSEMBLES HAVE SHOWN GOOD AGREEMENT OVER MUCH OF THE PERIOD IN THE HIGH LATITUDES AS THE UPPER FLOW TRENDS TOWARD INCREASED RIDGING INTO THE GULF BY NEXT THU/FRI. AN UPPER LOW INITIALLY OVER NW ALASKA IS FORECAST TO LIFT NORTH OF 70N MIDWEEK AS A LEAD SYSTEM WEAKENS THROUGH THE ALEUTIANS. THE MODELS HAVE ADVERTISED A RATHER DEEP 940S MB LOW IN THE WESTERN ALEUTIANS MON/D4 BEFORE SHEARING EASTWARD. THAT FRONT SHOULD DISSIPATE BY THE TIME IT REACHES THE GULF ON WEDNESDAY. NEXT SYSTEM BEHIND IT SHOULD PUSH THROUGH THE WESTERN/CENTRAL ALEUTIANS AND SOUTHERN BERING SEA IN RESPONSE TO MORE AMPLIFIED UPPER LOW AND BRING A SURGE OF MILDER AIR TO SW AND W ALASKA LATER NEXT WEEK. GFS WAS QUICKER THAN THE ECMWF SO A MIDDLE GROUND SOLUTION VIA THE BLEND WAS ACCEPTABLE. THAT FRONT MAY STALL OVER WESTERN AREAS AND THE EASTERN ALEUTIANS AS IT ENCOUNTERS BUILDING RIDGING TO ITS EAST. THE CONSENSUS AMONG THE 06Z GFS/GEFS (AND 12Z GFS AS WELL) ALONG WITH THE 00Z ECMWF/ECMWF ENSEMBLE MEAN OFFERED A GOOD STARTING POINT FOR THE FORECAST THAT WAS IN LINE WITH CONTINUITY. TRENDED TOWARDS MORE ENSEMBLE WEIGHTING WITH TIME THOUGH THE SYNOPTIC AGREEMENT REMAINED GOOD INTO NEXT FRIDAY. ANOMALOUS SURGE OF PRECIPITABLE WATER INTO SW ALASKA (+2 TO +3 STND DEV PER THE 00Z ECMWF AND +3 TO +4 PER THE 12Z GFS) SHOULD BRING IN MODEST/HEAVY PRECIPITATION (SOME RAIN GIVEN TEMPERATURES NEAR OR ABOVE FREEZING) TO THE Y-K DELTA REGION AND PERHAPS INLAND TO THE ALASKA RANGE AND/OR TOWARD THE WESTERN TANANA RIVER VALLEY. HEAVY SNOW MAY BE POSSIBLE GIVEN THE FORECAST SETUP. FRACASSO