Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 644 PM EST Sat Dec 11 2021 Valid 12Z Wed Dec 15 2021 - 12Z Sun Dec 19 2021 ...Overview... Today's guidance is consistent in showing a steady progression of upper features with varying amplitude. Associated surface waves and frontal systems will bring periods of precipitation to the Aleutians/Bering Sea, western/southern mainland, and Panhandle. This pattern should promote more moderate temperatures over many areas after a cold start to the period on Wednesday. ...Guidance Evaluation and Preferences... A consensus approach of a 12Z operational model composite for about the first half of the period followed by some inclusion of 12Z GEFS/00Z ECMWF means along with remaining model input provided fairly good continuity for significant features with only modest refinements. Clustering is good for initially strong Bering Sea low pressure/frontal system to weaken as it approaches the mainland by early Thursday, ultimately leading to a triple point wave evolving over the southern coast/Gulf of Alaska by Thursday-Friday as the supporting upper shortwave weakens. There is still some signal that the front may absorb a mid-latitude Pacific wave early in the period but perhaps with less obvious influence on southern coast/Gulf low pressure beyond what would already be supported by the approaching Bering Sea/Aleutians upper shortwave. Behind this system, models are gradually improving the definition of a compact wave that should reach the western Aleutians by early Thursday then track across the Bering Sea and into the mainland (while another southern coast/Gulf wave develops) during the rest of the week. Preference was to lean more toward the majority which was slower than recent GFS runs to varying degrees. The new 18Z GFS runs did nudge a little slower. Even with some spread among non-GFS solutions there was enough improvement in clustering to yield a stronger system in today's forecast blend. Then guidance is consistent with an upper ridge building from the Bering Sea into the mainland next weekend, ahead of a strong storm tracking near Kamchatka. Most operational model runs continue to show a somewhat stronger ridge than the means (especially the GEFS mean), favoring maintenance of at least half model weight later in the period. The amplifying upper trough east of the ridge should be most pronounced over the east-central Pacific while only a modest shortwave crosses the mainland Saturday into early Sunday. Most models/means suggest somewhat faster progression than seen in recent GFS runs, and again the new 18Z GFS has adjusted a bit in the direction of consensus. However the GFS scenario cannot be fully discounted given the amplifying evolution. ...Weather/Hazard Highlights... A Bering Sea storm and its leading front will spread light precipitation across the eastern Aleutians Wednesday and mostly light-moderate activity into western and southern parts of the mainland during mid-late week. A frontal wave that evolves over the Gulf of Alaska/southern coast of the mainland may also help to focus precipitation along the southeastern coast and Panhandle. This precipitation should be of moderate intensity though it could be briefly heavier over a few isolated locations. Then another wave/frontal system should bring light to locally moderate precipitation to the Aleutians and western-southern mainland as well as the Panhandle late in the week. Ahead of a storm tracking near Kamchatka, a broad area of moisture and strengthening winds will likely spread across portions of the Aleutians and Bering Sea during the weekend. Some of this moisture may reach the western mainland by next Sunday. Expect temperatures to trend warmer over most of the state (from southwest to northeast) after a cold start with below normal readings on Wednesday. This trend should bring above normal temperatures to at least the western mainland and parts of Southcentral by Friday, with coverage of above normal anomalies for min temperatures tending to be somewhat greater than for highs. Then a slight cooling trend is possible Saturday into Sunday behind low pressure, followed by a quick rebound in the west as low level flow turns southerly. Rausch 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