Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 247 PM EDT Wed Jun 19 2019 Valid 12Z Sun Jun 23 2019 - 12Z Thu Jun 27 2019 An upper level low just west of the Panhandle to start the medium range period (Sunday) will shift south and remain off the Northwest U.S. coast for the remainder of the period while upper level ridging builds across Alaska and holds strong through day 6. There is some indication in the models that troughing may start to break down the ridge across the northern mainland by day 7, with the GFS a bit more aggressive on this than the ECMWF or the ensemble means. Meanwhile, multiple shortwave perturbations will rotate around a broad upper level low anchored from the Kamchatka Peninsula of Russia to the far western Aleutian islands. Ensemble means continue to hint at a developing omega block across the Alaska region which would indicate this overall pattern being slow to change through the entire day 4-8 period. This sends a surface low into the Bering Sea and a cold front across the central Aleutians early next week with indications of a second system developing south of the Aleutians late in the period. Days 4 and 5 show good enough agreement to warrant a majority deterministic model blend (between the 12z GFS and 00z ECMWF), with smaller contributions from the ensemble means (GEFS/ECENS). After this time, increasing weighting of the ensemble means was used to mitigate the smaller and less predictable timing and detail differences with individual systems rotating around the western Aleutians trough. This results in a forecast fairly close to yesterdays continuity. In terms of the sensible weather, most places across the Mainland should be fairly warm and dry, with the best chance for showers across the elevated terrain of southern Alaska. Increased rain chances will be possible across parts of the central and western Aleutians as southerly flow ahead of the broad upper level trough advects moisture into the region and a series of surface lows move nearby. Santorelli 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 No significant hazards are expected over Alaska during this forecast period. 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