Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 630 PM EST Sat Jan 02 2021 Valid 12Z Wed Jan 06 2021 - 12Z Sun Jan 10 2021 ...Northeastern Pacific/Gulf of Alaska and Aleutians storms to bring potential for significant precipitation/strong winds... ...Overview and Guidance/Uncertainty Assessment... Guidance continues to advertise a stormy period, with one area of focus over the northeastern Pacific and vicinity while a deep system expected to track along the Aleutians from late Fri into the weekend becomes an increasingly dominant feature late in the forecast. Relative predictability/confidence of specifics for these two areas are fairly similar to recent days with the Northeast Pacific region significantly lower than for the Aleutians system. For the Northeast Pacific, forecast preferences incorporated operational guidance that best matched the general pattern of the ensemble means which among themselves offered good clustering in light of operational model spread and run-to-run variability. This led to using the 12Z/00Z ECMWF and 12Z/06Z GFS (slightly more weight to the 12Z runs early-mid period) as the primary input--leading to a somewhat stronger version of the means. In light of the differences among even the GFS/ECMWF runs for the initial storm near Kodiak Island, plus greater differences in the CMC/UKMET, confidence is still not especially great. The forecast appears to be quite sensitive to the exact details of flow aloft between a mean trough extending from the northern/eastern Bering into the northeastern Pacific/Gulf and a western Canada ridge that could extend its influence into the mainland at times. Thus it is yet to be determined whether the Kodiak Island system may linger in that vicinity for a time (majority consensus) or perhaps lift northward but still leave behind residual low pressure in that area. During next weekend the ensemble means generally side with an average of the past two ECMWF runs for the general evolution of another northeastern Pacific system, with faster northwestward motion than seen in the 12Z GFS. At least in terms of timing the 06Z GFS was closer in principle but was a bit northward. Thus far the models and ensembles have been fairly consistent and agreeable for the late Fri into weekend Aleutians system, though some east-west spread does develop with time. Recent ensemble mean trends add support for depth closer to the operational models, possibly into the 950's mb by early Sat--quite strong though not as extreme as its recent predecessor. Thus the operational model focus in the blend extended into day 7 Sat with only 20 percent total input from the GEFS/ECMWF means. Ensemble mean input increased somewhat for day 8 Sun in light of increasing model divergence for the system farther east. ...Weather/Hazards Highlights... One or more northeastern Pacific/Gulf systems should bring a multi-day period of occasionally moderate to heavy precipitation to areas along the southern coast and Panhandle. Best confidence in highest five-day totals extends from near the Kenai Peninsula eastward. Locations farther west will be more sensitive to the exact track of low pressure centers. These systems may produce one or more episodes of brisk to strong winds as well. Meanwhile strengthening winds and increasing precipitation should reach into the western Aleutians around Fri and then extend across the rest of the islands during the weekend as the associated storm progresses eastward. The upper level pattern will favor establishment of above to well above normal temperatures over most areas during the period. Locations over the extreme northern and western mainland will likely be the last to see above normal readings. The above normal anomalies for min temps should generally be greater than those for max temps. Rausch Additional 3-7 Day Hazard information can be found on the WPC medium range hazards 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