Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 522 PM EST Tue Nov 10 2020 Valid 12Z Sat Nov 14 2020 - 12Z Wed Nov 18 2020 ...Guidance/Predictability Assessment... From late this week into the weekend there is good agreement on the slow moving upper low dropping southeast into a Northeast Pacific mean trough. A deep layer ridge drifts east across the Bering Sea may decelerate as it eventually reaches the eastern Bering Sea and possibly parts of the mainland. Forecast details become increasingly uncertain with time as recent guidance diverges with how shortwave energy emerging from eastern Asia this weekend evolves. The significant differences then increase in scale and eastward effect going into next week. Since each of the global models has a storm developing in the Pacific east of Asia, the primary debate is in the phasing/timing details. This wave would develop into a deep storm that reaches the vicinity of the western Aleutians/Bering early next week followed by added uncertainty over strength/track as it heads into the mean ridge aloft downstream. Another scenario that some guidance has been advertising is for greater northern stream emphasis, leading to a farther northwest primary low and a mere front crossing much of the Aleutians/Bering. Over the past couple days or so operational GFS/ECMWF runs have varied significantly between each other and from run to run within the broad envelope of possibilities for the Bering Sea/northern Pacific evolution. As is typical, there is better than usual agreement among the Canadian/GFS/ECMWF ensemble means on the timing. For Sat-Sun an operational model blend was used to forge a consensus. For the early to middle portions of next week, greater weighting was given to the ensemble means. Lesser weighting was given to the last 2 runs of the ECMWF and GFS, given they are still changing run to run. This keeps low pressure over the western Bering with progressive leading front. Modest input of individual models helps to sharpen the intensity of the low pressure centers. oft over the region. Meanwhile there is better consensus toward surface high pressure building over more of the northern mainland from late this weekend into early next week. ...Weather/Threats Highlights... Scattered showers are forecast to occur Days 4-5 over coastal southwest AK, the Aleutians, and southeast Alaska. The next system over the north Pacific brings a threat of showers or even a period of rain to the Aleutians Day 6 and 7. So far guidance has displayed poor agreement/continuity for the details. The cooling trend forecast to be in progress late this week will continue into the weekend, leading to below normal temperatures over a majority of the mainland and Panhandle by the weekend and early next week. The main exception will be over the North Slope where above normal readings should develop in the middle of next week, according to the ensemble means. Petersen 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 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