Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 157 PM EST Fri Jan 26 2018 Valid 12Z Tue Jan 30 2018 - 12Z Sat Feb 03 2018 Another day's worth of guidance has done little to improve the low confidence for some details within an expected blocky regime. This lack of confidence is due to a combination of meaningful differences persisting for the strength/position of a strong upper high initially over/near eastern Siberia, energy to the southeast of this high, and uncertain degree of interaction with central Pacific mean troughing. Over the past day the ECMWF has maintained a stronger upper high relative to GFS runs with the 00z UKMET/CMC also quite strong. However at the same time the ECMWF has made a notable southward adjustment in upper high position which is a nod to the CMC which has been on the southern edge of guidance. The combined strength and southern position of the 00z ECMWF/CMC falls within the minority of 00z GEFS/ECMWF/CMC ensembles. On the other hand the northern and/or weaker GFS/GEFS scenario does not appear to be the most likely either. The 12z GFS provides further intrigue by having the upper high drift farther northwest than most recent runs or other models. Partially due to the differences with the upper high, there are widely differing depictions for energy to the south, both in shape and location. Retrograding upper lows in 00z/06z/12z GFS runs have become more the minority relative to the full array of models through arrival of the 12z GFS and the weakness aloft that sets up over the mainland in GFS runs is on the northern side of the spread. On the other hand the strong/southern ridge in the 00z ECMWF/CMC leads to an overall mainland and north Pacific/Aleutians pattern that is more suppressed than even the ECMWF mean. Meanwhile guidance in principle is still signaling that a brief/modest wave may exist over or near the Gulf of Alaska around day 5 Wed in response to southern mainland-Gulf of Alaska energy aloft, and then this energy and/or central Pacific trough energy bringing one or more retrograding northern Pacific surface lows close to the Aleutians. There is a scattering of ensemble members bringing low pressure farther north into the Bering Sea as in some recent GFS runs but the average of ensemble means over the past 1-2 days has favored a track over or just south of the Aleutians. Overall prefer to maintain a conservative forecast close to the middle of the spread with relatively modest change in continuity, given the wide variation among individual solutions. After a blend of 00z-06z GFS and 00z ECMWF/UKMET/CMC runs for day 4 Tue, the rest of the forecast incorporated ideas from both model and ensemble solutions by way of somewhat more ECMWF input (combination of 00z and 12z/25 runs since the older run compared a little better to ensembles) than GFS, and more 00z ECMWF mean weight than 06z GEFS. The end result nudged the southern mainland/Gulf of Alaska pattern a bit southward versus yesterday's forecast. Significant changes in remaining 12z guidance seem to confirm the intermediate preference, as the ECMWF/CMC/UKMET have all trended less suppressed than prior runs with the general pattern-- but remaining south of the GFS-- and now show upper low energy retrograding into the Aleutians. Rausch