Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 324 PM EDT Fri Nov 02 2018 Valid 12Z Tue Nov 06 2018 - 12Z Sat Nov 10 2018 From day 4 Tue into early day 5 Wed a blend of the 06Z GFS/00Z ECMWF represented consensus well for most significant features, and with only modest refinement from continuity. Primary systems of note will be strong albeit weakening low pressure tracking from the northern Bering Sea through extreme eastern Siberia or the Bering Strait, and a central Pacific system tracking into the northeastern Pacific by Tue-Wed. To the east expect fairly sharp upper ridging to drift eastward toward northwestern Canada. At the same there should be low amplitude/progressive mean flow immediately upstream from the upper low/trough supporting the initial northern Bering system. Then from late day 5 onward confidence in specifics rapidly decreases as model/ensemble solutions diverge among each other and among consecutive runs. One area of considerable uncertainty involves the progressive flow emerging from eastern Asia and reaching the Bering by Wed-Thu. Solutions range from maintaining a diffuse open shortwave that produces a fairly modest frontal system with possible embedded waviness (like GFS runs through the 06Z cycle) to significant concentration of energy that leads to well-developed Bering system (06Z FV3 GFS, 12Z GFS). The 00Z ECMWF is essentially a compromise while other operational models seem to favor the northwestern-northern Bering for any defined surface low. Ensemble spread is sufficiently great to result in a fairly weak surface depiction overall but the means favor keeping lowest pressures in general over the northern Bering. Overall preferred a conservative model/mean approach involving the 06Z GFS/00Z ECMWF and their ensemble means while awaiting more confident adjustments/trends. By days 7-8 Fri-Sat the 00Z-06Z GFS/00Z ECMWF and the ensemble means show better than average agreement for forecasts that far out in time with respect to a possibly strong low pressure tracking over the northwestern/northern Bering. This clustering however disguises the significant continuity changes that have taken place over the past day in most of the guidance, including the ECMWF mean. What happens with the mid-late week Bering energy/possible low pressure is also a wild card as the best-developed solutions here lead to differing evolutions for late period flow. There will be potential for a period of strong winds/focused precipitation with one of these systems, even if confidence is well below average for each one individually. As with the preceding feature, preferred the 06Z GFS/00Z ECMWF and their means as the best option at this time. Meanwhile over the northeastern Pacific, low pressure tracks diverge for low pressure approaching the Alaska Panhandle. Solutions for this system hinge upon exactly how much interaction there is with flow to the west. The combination of ensemble trends over the past day and current spread at least favor a track that leans away from the southern part of the spread (00Z/06Z GFS), with the 12Z GFS adjusting closer to the 00Z ECMWF track. However even with the narrowing of the southern side of the spread there is not yet a clear signal favoring either side of the remaining spread between operational runs and farther north ensemble means--recommending a model/mean blend similar to that used for mid-late period evolution farther to the west. The current solution envelope leads to a fair degree of uncertainty for precise coverage/duration/intensity of precipitation over the southeastern coast of the mainland and northern Panhandle. There seems to be a somewhat greater margin for error to yield similar precipitation totals over the southern Panhandle. Rausch WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can be found at: http://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif http://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html