Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 640 PM EST Sat Mar 07 2020 Valid 12Z Wed Mar 11 2020 - 12Z Sun Mar 15 2020 ...Overview and Guidance/Predictability Assessment... Early in the period guidance agrees fairly well that mainland upper troughing from the short range will continue into northwestern Canada while upstream energy filtering into a Gulf of Alaska trough will progress southeast and push away initial low pressure near the Panhandle. At the same time cold high pressure should prevail over much of the mainland during Wed-Thu. Farther west the forecast is fairly consistent in principle for a strong storm to track across Siberia and into the Arctic late this week. Expect the storm's associated strong winds to cross the Bering Sea and northwest mainland with some significant terrain-enhanced precipitation possible. The most notable adjustment in most guidance over the past two days is a pronounced stronger trend for upper ridging now forecast to build over the northeastern Pacific into the mainland Fri-Sun. This trend has continued with the 12Z guidance including the 12Z ECMWF/ECMWF mean runs (12Z ECMWF mean arriving after initial guidance evaluation). While it reflects recent trends the 12Z CMC could be overdone with this ridge. The stronger trend for the upper ridge provides ongoing support for discounting the GEFS mean whose recent runs have been on the eastern side of the spread for the Siberia into Arctic storm, corresponding to mainland heights aloft that are generally somewhat lower than most other guidance. Later in the period the models and individual ensemble members become increasingly divergent regarding the details of the overall ridge and energy that may flow around it. This favors trending the forecast increasingly more toward the ensemble means (00Z ECMWF mean and 12Z NAEFS mean, to lean away from questionable GEFS mean characteristics) until better agreement develops. Most D+8 multi-day means--which cover the latter part of the extended period and beyond--are fairly similar in principle so resolving differences on a specific valid day seems to be a low-confidence endeavor. The Wed into early Thu part of the forecast started with the 12Z ECMWF/GFS/UKMET/CMC in order of greatest to least weight. One localized reservation about the GFS exists south of the Panhandle as it shows a northeastward-tracking wave versus consensus that depicts a system generally developing in place and then progressing southeastward. Strength of the CMC upper ridge led to its removal from the blend after early Thu. Total weight of the 00Z ECMWF mean and 12Z NAEFS mean was 20 percent on day 6 Fri and increased to 50 percent Sat and 70-80 percent by next Sun. ...Weather Highlights/Threats... The southeastern coast and Panhandle will see a drier trend mid-late week as initial low pressure nearby weakens/departs. Trailing high pressure over the mainland will bring much below normal temperatures through midweek, followed by a significant warming trend that initially arrives over western-northern areas and progresses eastward. Still expect the greatest above normal temperatures from late this week into the weekend to be over the northern mainland. The strong storm responsible for this temperature rebound, tracking northeast through Siberia and into the Arctic Thu-Fri, should also bring a period of strong winds across the Bering Sea and into the northwestern mainland with significant terrain-enhanced precipitation likely. Recent trends with the upper ridge building over the northeastern Pacific into the mainland suggest that the strongest winds/heaviest precipitation may not extend as far southeastward as suggested in some earlier projections. By next weekend confidence is quite low regarding any possible features that could flow around the mean ridge aloft, though the general pattern may support some precipitation over northern/western parts of the mainland. 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