Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 649 PM EDT Tue Jul 13 2021 Valid 12Z Sat Jul 17 2021 - 12Z Wed Jul 21 2021 ...Overview... Blocky pattern will start to break down and move east during the medium range, but with continued troughing into the Bering. An upper low near Haida Gwaii will very slowly move into British Columbia with weakening ridging over the Interior that will move into the Yukon. This will keep northwestern areas rather unsettled as a lead and secondary frontal system move into the region. ...Guidance/Predictability Evaluation... The ensembles had a good handle on the overall longwave pattern through the period, but with less predictability over the Bering by next week. The trend has been a bit quicker overall with the pattern breakdown/shift roughly west of 150W for the weekend period but an unclear trend for next week. For the lead system, the 12Z GFS/ECMWF paired rather well with the means as the upper and surface system move into western Alaska before weakening/dissipating around next Monday as it bumps into ridging. Used a large deterministic component given the good agreement, though the UKMET and Canadian were not quite as agreeable. Around the Panhandle, the upper low will only slowly move eastward into British Columbia, perhaps after a wobble or two as a shortwave rounds the base later this weekend. For the next Bering system, models diverge on which incoming shortwave may take precedence and such a determination is not yet discernible. Blended in an increased weighting of the ensemble means to account for the uncertainty. The ECMWF was quicker than its mean but the GFS was the opposite, so a middle ground solution was preferred for now. Across the North Slope, flatter flow will support a wavy boundary as a couple areas of low pressure traverse the Beaufort/Arctic. ...Weather/Threats Highlights... Precipitation will be focused over western/northwestern areas during the period under southwest flow, as well as across the Aleutians along the tail-end of the frontal boundaries. Widespread tenth to a quarter inch with focused half to one inch rainfall (locally more) is possible over northwestern areas over a 1-2 day period with each system. Lighter precipitation will overspread parts of the North Slope/Brooks Range as well, especially by next week. Portions of the North Slope/Brooks Range and Panhandle/southeast corner of the mainland should see the most persistent below normal highs during the period, though northern areas may see some day-to-day variability depending on frontal position right along the coast. Moisture arriving from the west during the weekend into next week will bring a cooling trend from west to east, with increasing coverage of below normal highs. On the other hand low temperatures will tend to be more above normal with only smaller areas of below normal anomalies. Fracasso 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 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