Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 753 PM EDT Mon Apr 10 2023 Valid 12Z Fri Apr 14 2023 - 12Z Tue Apr 18 2023 ...Cold pattern for much of Alaska continuing into next week... ...Overview... Most guidance shows some form of upper troughing over and south of the mainland through the period, with a mean upper low tending to reside over the northeastern Pacific/southern Gulf of Alaska. Consensus also shows cyclonic flow farther north over the Arctic at least through the weekend, with some energy potentially dropping south over the mainland. This pattern will support well below normal temperatures over most of the state through early next week and Climate Prediction Center Forecasts suggest chilly conditions may persist beyond the medium range forecast period. The circulation around northeastern Pacific low pressure should support periods of precipitation across the Panhandle and parts of the southern coast with mostly light/scattered snow elsewhere. With high pressure expected to drift from eastern Siberia across or north of the northern coast of the mainland, much of the state will be in the gradient between this high and Pacific low pressure. ...Guidance Evaluation/Predictability Assessment... One notable question mark as far as embedded details go is the handling of an initial upper low generally forecast to be over the western mainland early in the period. Latest ECMWF runs have been on the deep and slow side, maintaining enough definition as it drops south of the mainland pull Pacific/Gulf low pressure back close to Kodiak Island by early day 6 Sunday (with corresponding higher QPF over that region). At least compared to the prior run, the 12Z ECMWF is weaker so it does not bring the surface low as far westward as before (even though the new run's upper low is farther west). On the other hand, the GFS is on the weak side of guidance. A blend of 12Z operational models, with the ECMWF contribution split with the 00Z ECMWF mean to blunt the influence of less confident operational ECMWF details, provided a reasonable representation of guidance overall as there are ensemble hints of some defined energy still being over the southwestern mainland into early Sunday. At the surface, this blend kept the forecast close to continuity and an average of the ensemble means for northeastern Pacific/southern Gulf low pressure. During the first part of next week guidance diverges regarding whether Arctic troughing persists, possibly feeding additional energy southward into the mainland, or some ridging at least briefly builds across higher latitudes. At the moment the guidance is close to evenly split. The 12Z ECMWF/CMC are in the ridge cluster and the 00Z/12Z ECMWF means show a less pronounced variation of that. GEFS/CMCens means and 00Z through 12Z GFS runs constitute the persistent trough cluster, while the new 18Z GFS now shows enough of a ridge to produce a brief break in Arctic troughing. Transitioning the forecast to 50-60 percent means with the rest lingering components of the 12Z GFS/ECMWF/CMC by days 7-8 Monday-Tuesday ultimately yielded troughing, but sufficiently weak to facilitate adjustment toward an alternate scenario if guidance trends dictate. Some recent guidance had been showing North Pacific energy progressing through the upstream mean ridge and possibly influencing the evolution over the northeastern Pacific by the end of the period. CMC means have been a northern extreme with this energy and associated surface reflection, though the 12Z run has adjusted somewhat south. With the 12Z runs, remaining guidance seems to become more emphatic about upper/surface ridging persisting over and north of the Aleutians with any upper trough/low and surface system remaining quite far south of the Aleutians. Still, guidance shows plenty of spread for exact details within the general mean pattern over the northeastern Pacific--favoring the blended/mean approach late in the forecast. ...Weather/Hazard Highlights... A significant highlight of the forecast will be the much below normal temperatures, with anomalies tending to be most extreme for daytime highs and during late this week into the weekend. As the initial mainland upper low drops southward out of the area, a modest rise in heights aloft could lead to a little moderation but with many areas likely remaining well below normal. Morning lows could eventually settle slightly above normal over some locations over the northern part of the mainland and the Panhandle/Southcentral. Flow around northeastern Pacific low pressure should bring periods of coastal rain and inland/mountain snow across the Panhandle and southern coast. There may be some locally enhanced activity at times but most totals should be in the light to moderate range. Elsewhere snow should be fairly light and scattered. Meanwhile, the tight gradient between Pacific low pressure and Bering Sea high pressure will support breezy to windy conditions over the eastern Aleutians and southwestern Alaska Peninsula, with strongest winds likely to be from late this week through the weekend. Rausch Hazards: - High winds across the eastern portion of the Aleutians to the southern portion of the Alaska Peninsula, Fri-Sun, Apr 14-Apr 16. - Much below normal temperatures across western and southwestern Alaska, Thu-Sun, Apr 13-Apr 16. 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