Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 644 PM EST Fri Feb 28 2020 Valid 12Z Tue Mar 03 2020 - 12Z Sat Mar 07 2020 ...Overview and Guidance/Predictability Assessment... Overall today's guidance shows better than average agreement with the pattern evolution and significant systems during the period, though with typical spread and variability for specifics. Expect amplifying upper trough energy to drop through the central-southwestern mainland/Bering Sea and into the Gulf of Alaska/northeastern Pacific, likely with an embedded upper low reaching the Gulf around Wed. The trough/upper low should continue southeastward late this week into the weekend. Farther west consensus shows a system reaching the Aleutians/Bering Sea by Thu followed by a steady weakening trend. An upper ridge will likely build across the Bering into parts of the mainland ahead of this system, followed by another ridge Sat as guidance brings a strong system from the western Pacific into the western Bering Sea. Higher latitude flow should tend to be progressive and will trend toward lower-predictability shortwave specifics with time. From the start of the period Tue into early day 6 Thu, a blend of the 00Z-12Z ECMWF and 12Z GFS/UKMET provided a good representation of consensus evolution with better detail than the means while accounting for existing spread with specifics. This cluster suggests that Gulf of Alaska low pressure on Tue-Wed should weaken as a North Pacific wave ultimately tracks east-northeast to a position just south of the Panhandle in response to the upper dynamics dropping into the Gulf/northeastern Pacific. The 12Z CMC strays from this cluster with a farther northward North Pacific wave. Remaining guidance still shows some spread and variability for the exact track of the North Pacific wave so confidence in a specific forecast is only moderate. The ensemble means show a mere hint of the North Pacific wave and ultimately merge it into the southeastward-moving Gulf low. Meanwhile latest operational runs agree in principle on a well-defined Aleutians/Bering system around Thu with subsequent weakening since it is passing through a larger scale mean ridge aloft. The past couple ECMWF mean runs are still weaker than most operational runs but at least show better definition than the other means. After early Wed the forecast adjusted to a model/ensemble mean blend, reaching half of each by day 8 Sat. At that latter time frame the preference was to reduce 12Z GFS weighting somewhat as it strayed somewhat faster than most other guidance with leading height falls aloft and surface front extending from the strong western Pacific/Bering system. However the 12Z ECMWF mean has come in faster than its previous run or the 00Z/12Z ECMWF so the GFS scenario looks less extreme now. ...Weather Highlights/Threats... Initial low pressure over the Gulf of Alaska will bring precipitation (mostly snow) to the Panhandle and southeastern corner of the mainland through midweek with additional precip possible into late week depending on the exact track of the North Pacific system that may reach south or southwest of the Panhandle. An area of light-moderate precip will accompany the system forecast to reach the Aleutians/Bering around Thu and then gradually shear out and/or track southeastward. Strong low pressure tracking from the western Pacific into the western Bering Sea late this week into the weekend will bring a broad area of moisture and brisk winds across the Aleutians/Bering Sea. Below to much below normal temperatures will prevail over a majority of the state into the latter half of the week. Western areas should start to see a warming trend by around Thu-Fri with temperatures moderating from west to east into Sat. 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 Hazards: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Mon, Mar 2. - Much below normal temperatures across portions of mainland Alaska, Mon-Fri, Mar 2-Mar 6. - Much below normal temperatures across portions of mainland Alaska, Tue-Fri, Mar 3-Mar 6. 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