Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 634 PM EDT Tue Jun 23 2020 Valid 12Z Sat Jun 27 2020 - 12Z Wed Jul 01 2020 ...Overview and Weather/Hazard Highlights... Two low pressure/frontal systems are expected to affect Alaska early in the extended forecast period, one across the Aleutians, and another across portions of western/northwestern mainland Alaska. A relatively deep low pressure system forecast to cross the central Aleutians Sat-Sun will bring showers and gusty winds, which could extend along a front as far east as the Alaska Peninsula. Rain (and high elevation snow) showers may persist into early next week across mainland Alaska as this system pushes inland and dissipates. Farther north, low pressure north of Siberia will accompany a frontal boundary across the Bering Strait and into western mainland Alaska Sat-Mon. This system is expected to produce areas of heavy rain and some mountain snow across portions of northwest mainland Alaska, with the potential for high winds across areas close to the Bering coast over the weekend. While widespread precipitation across mainland Alaska should gradually subside toward the middle of next week, persistent broad cyclonic flow will result in continued unsettled conditions, with persistent clouds and precipitation especially across mountain ranges. The widespread clouds and precipitation will also result in below average temperatures for most of the state through much of the extended period, with highs forecast to be 5 to 15 deg F (even 20 deg for a few locations) below average. ...Guidance/Predictability Assessment... The 12Z ECMWF was used heavily during days 4-5 (Sat-Sun), with a shift to majority weight placed on ECENS/GEFS ensemble means during days 6-8 (Mon-Wed). The ECMWF was representative of consensus early on. Deterministic model differences began to grow rather quickly from day 6 onward, with respect to the evolution of the upper low and frontal system affecting western mainland Alaska, and on the timing of an additional shortwave/low pressure system crossing the North Pacific toward the middle of next week. Differences among ensemble means with respect to these features were smaller, with also some greater degree of consistency among ensemble relative to the deterministic guidance - thus, supporting the trend toward ensemble means from day 6 onward. Ryan 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 rain across portions of northwest mainland Alaska, Sat-Sun, Jun 27-Jun 28. - High winds across portions of northwest coastal Alaska, Sat-Sun, Jun 27-Jun 28. 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