Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 655 PM EST Thu Jan 05 2023 Valid 12Z Mon Jan 09 2023 - 12Z Fri Jan 13 2023 ...Overview and Guidance/Predictability Assessment... Guidance shows significant uncertainties regarding upper flow over the mainland during the period, between somewhat more agreeable western Canada ridging and another ridge that may drift from the Bering Sea into Siberia. Meanwhile the succession of low-predictability northeastern Pacific/Gulf waves around the western side of the western Canada upper ridge may continue to some degree, with the northern periphery of a leading Pacific system tracking well south of the Aleutians early in the week possibly having some influence on these waves thereafter. Distribution/intensity of precipitation near the southern coast and Panhandle will depend on the combined details of the mainland's upper pattern and northeastern Pacific/Gulf waves. A trailing system initially emerging over the western Pacific should track close to the Aleutians by the latter half of the week. Regarding the pattern over the mainland, individual solutions range from the 12Z GFS that extends the Canada ridge all the way back through the mainland and beyond (latest 6-hourly GFS runs have been very erratic with 00Z/06Z/18Z runs having very different ideas), while on the other extreme by day 6 Wednesday the 12Z UKMET/CMC bring an upper low into the central/southwestern mainland respectively. Recent ensemble mean runs have been gradually trending toward an upper trough over the northwestern mainland/western coast, with the 00Z/12Z ECMWF runs being the closest operational runs to this scenario (after the ECMWF had been showing a lot more ridging over the western mainland--the same ridge now expected to lift into Siberia). Given the uncertainty of the forecast, prefer the lean toward a majority scenario of troughing but in moderate form as offered by the ECMWF runs and ensemble means. A weaker version of the CMC would also fit into this cluster early in the period. This scenario would support establishment of a northeast-southwest surface front to the east of the upper trough. Elsewhere, after a wave that could reach the southern coast early day 4 Monday, there is minimal agreement for any additional northeastern Pacific waves that would help to enhance precipitation along the southern coast. The uncertainty is compounded by issues with the mainland flow pattern in addition to the low-predictability nature of the waves themselves. Aside from the 12Z GFS, consensus generally keeps most influence from the leading mid-latitude Pacific storm south of the Aleutians. On the other hand the next system should track much closer to the Aleutians by mid-late week. Some GFS runs have been a bit on the fast side with this system for at least parts of the period. An average among the ECMWF runs, 12Z CMC, and ensemble means would provide a good starting point for this feature. Based on forecast considerations over the mainland, the initial blend started with half total weight of the 00Z/12Z ECMWF runs, 30 percent ensemble means (12Z GEFS/CMCens and 00Z ECens), and 20 percent 12Z CMC for days 4-5 Monday-Tuesday. Then the forecast phased out the CMC while raising the ensemble mean weight to 50-60 percent mid-late period while holding on to the ECMWF runs for operational input. The new 12Z ECMWF mean arriving after forecast preparation provides good support for this overall approach. ...Weather/Hazards Highlights... Precipitation along the southern coast may trend lighter for at least a brief time early in the week, with the Panhandle also looking to be fairly dry as well. The overall pattern may support some return of moisture to the southern coast and/or Panhandle by mid-late week, but with low confidence for the specifics of coverage and intensity. Areas farther north over the mainland could see some light/scattered snow depending on the character of a possible upper trough/embedded low currently expected to evolve over the far northwest/west coast, and surface front to the east of the upper trough. The system emerging from the western Pacific should begin to affect the Aleutians around Wednesday with an increase of precipitation and possibly winds, with the moisture likely to continue eastward across the islands thereafter. Temperatures over some areas will depend on the exact details of uncertain flow aloft. Currently expect upper troughing over the far western mainland to support below normal highs in its vicinity, with below normal highs also possible over the interior. Min temperatures should generally have greater coverage of above normal anomalies, with best potential for any below normal readings tending to show up over the west/interior after midweek. Rausch No significant hazards are expected over Alaska during this forecast period. Additional 3-7 Day Hazard Information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can also be found at: https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html