Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 643 PM EST Sat Feb 29 2020 Valid 12Z Wed Mar 04 2020 - 12Z Sun Mar 08 2020 ...Overview and Guidance/Predictability Assessment... Latest models and ensembles still display better than average agreement and continuity for significant features during the days 4-8 Wed-Sun period. There have been some differences/trends with various specifics, typical for forecasts several days out in time. The unusually good consensus in principle allowed for an operational model blend (12Z GFS/ECMWF/UKMET/CMC) to start the forecast days 4-5 Wed-Thu and maintaining 70 percent total operational GFS/ECMWF weight relative to the 12Z GEFS/00Z ECMWF means even into day 8 Sun. An amplifying upper trough, anchored by a closed low likely to be tracking near the Kenai Peninsula very early Wed, should progress southeastward with time and encourage a similar path for one or more surface lows over the Gulf of Alaska/Northeast Pacific. Exact details for low pressure are still murky though. Consensus has held steady for the initial low off the Kenai Peninsula early Wed but most models aside from the 12Z UKMET have backed off somewhat from the development of separate low pressure to the south and reaching a position south of the Panhandle. The aforementioned model blend provided a reasonable account for the ongoing uncertainty. By early day 5 Thu this yielded a surface low a bit west of the ensemble means--which admittedly have been more stable than individual model runs over the past day. Meanwhile the ensemble means are still in the process of catching up to the operational runs in representing the definition of the system forecast to affect the Aleutians/Bering Sea and parts of the Alaska Peninsula Thu-Fri. The latest model average has trended somewhat stronger from yesterday. 12Z ECMWF trend to divert a greater proportion of upper dynamics and surface low pressure to the southeast after early Fri aligns well with most other latest guidance. The 12Z CMC strays from the majority cluster after early Fri with minimal other support for its idea of low pressure tracking into the western mainland. Thus the CMC was dropped from the forecast blend after 12Z Fri. Given the days 7-8 time frame, the GFS/ECMWF runs and GEFS/ECMWF/CMC ensemble means are remarkably similar and consistent for the storm forecast to emerge over the western Pacific around midweek and track into the western/northern Bering Sea next weekend. Consecutive cycles have varied a bit for track/timing but an overall average has provided good continuity. The unusually good guidance clustering (not counting the slower/weaker CMC) allowed for keeping greater than usual operational model weight through the end of the period. Expect the upper ridge ahead of this system to progress from the Bering Sea through the mainland late week through the weekend. At higher latitudes expect northwesterly flow aloft early in the period followed by more westerly progressive flow on average with increasingly uncertain shortwave details over the Arctic and into the mainland. ...Weather Highlights/Threats... Corresponding to the progress of low pressure over the Gulf/northeastern Pacific, precipitation over the southeastern corner of the mainland and Panhandle should gradually decrease in coverage and intensity from northwest to southeast during the latter half of the week. An area of precipitation and brisk winds will accompany the system expected to affect the Aleutians/Bering Sea and parts of the Alaska Peninsula around Thu-Fri. The system likely to track into the western/northern Bering Sea next weekend should bring a broad shield of moisture and large area of brisk to strong winds across the Aleutians/Bering Sea and eventually into the mainland. Some locations in the southwestern half of the mainland will see the best potential for focused precipitation by the latter half of the weekend. The change in pattern over the course of the period will lead to a pronounced warming trend from initially well below normal temperatures. The North Slope region should be first to see readings rebound to the above normal side of the spectrum, followed by warmer air spreading from west to east over central/southern areas. Some locations over the extreme east/Panhandle could still be below normal into next Sun though. 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