Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 652 PM EST Tue Mar 08 2022 Valid 12Z Sat Mar 12 2022 - 12Z Wed Mar 16 2022 ...Overview... Latest guidance maintains the idea that a strong shortwave rounding the top of a Siberia upper ridge during the weekend will drop southward into the mainland early next week, leading to a northeast-southwest oriented upper trough. This feature and possibly additional energy arriving from the northeast may ultimately lead to an embedded upper low reaching near the southern coast/southwestern mainland by the middle of next week. Farther south and within fairly active Pacific flow, a strong mid-latitude system should weaken somewhat as it approaches the Panhandle early next week. At the same time a trailing system will likely track just south of the Aleutians, but with some uncertainty over what interaction may occur between it and initial low pressure/upper dynamics lingering over the Aleutians. Some details of these Pacific systems will depend on exactly how the upper trough over the mainland evolves. ...Guidance/Predictability Assessment... Deeper ensemble mean trends for the developing mainland upper trough early next week, most noticeable starting with the daytime runs from Monday, are adding support to the recent operational model consensus that has been showing a rather deep trough. The primary forecast considerations are that the 12Z and new 18Z GFS runs ultimately pull the embedded upper low farther southwest than most other guidance (leading to a greater westward extent of precipitation along the southern coast late in the period) and the UKMET being a little slow with the arriving feature through the end of its run early Monday. The 06Z GFS compared much better to the model/mean majority through the period. At the moment the latest ensemble means and ECMWF/CMC/06Z GFS are quite similar by day 8 Wednesday in showing an upper low around the far southwest corner of the mainland. Regarding Pacific systems, there are still important track/evolution differences for the leading low tracking toward the Panhandle early next week. The past couple ECMWF runs have been on the southern side of the spread at that time but the 12Z run did at least trend north of its previous run. Remaining models and means show a somewhat farther north track and/or northward elongation or redevelopment in response to the amplifying mainland upper trough. Meanwhile guidance has been inconsistent with some details of the system tracking south of the Aleutians, partially due to uncertainty over how much interaction may occur with residual dynamics/low pressure over or near the Aleutians. The 12Z ECMWF is somewhat on the northern side of the spread. By late in the period the ensemble means agree that the primary focus for low pressure should eventually gravitate to the northeastern Pacific/Gulf of Alaska due to the mainland upper trough. Guidance comparisons led to starting the first half of the forecast with the 06Z GFS and 12Z ECMWF/CMC/UKMET, with least weight on the UKMET. Mixing in 30 percent total weight of the 12Z GEFS/00Z ECMWF means for days 7-8 Tuesday-Wednesday provided a reasonable balance of accounting for increasing detail uncertainties while reflecting recently increasing support for a mainland trough tilted somewhat more to an operational model consensus. ...Weather/Hazard Highlights... The primary precipitation focus during the period should be along the southern coast and Panhandle. Initial light to locally moderate activity will likely trend gradually lighter and more scattered during the weekend. Then expect low pressure tracking toward the Panhandle by Monday to increase precipitation over at least parts of the region, with moisture possibly expanding back along the southern coast depending on how the mainland upper trough evolves. Current forecast preference would lead to less westward extent along the southern coast than indicated by the 12Z/18Z GFS runs. Another system reaching the Northeast Pacific/Gulf of Alaska may enhance precipitation around Wednesday. It will take additional time to resolve the finer details of precipitation coverage and intensity during Monday-Wednesday. The Aleutians may see periods of mostly light precipitation and there is still uncertainty over the effects of low pressure forecast to track to the south early in the week. Guidance consensus shows brisk to strong northerly winds spreading across the Bering Sea and Aleutians by Tuesday-Wednesday. During the weekend, above normal temperatures will prevail over the southern mainland and North Slope with below normal readings (especially for highs) in-between and over the eastern mainland. The upper trough settling into the mainland by early next week should promote a colder trend with expanding coverage of below normal anomalies. Some pockets of above normal readings could linger over the North Slope and for min temperatures in the far south. Expect most of the Panhandle to see below normal highs through the period and a mix of above or below normal lows. Rausch 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 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