Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 718 PM EDT Wed Jul 14 2021 Valid 12Z Sun Jul 18 2021 - 12Z Thu Jul 22 2021 ...Overview... Blocky pattern will start to break down and move east during the medium range, but with continued/renewed troughing into the Bering and Bering Strait. An upper low initially near Haida Gwaii Sunday will very slowly move into British Columbia as weakening ridging over the Interior/Southcentral moves into the Yukon as the pattern relaxes. This will keep western areas rather unsettled as a lead and secondary frontal system move into the region. ...Guidance/Predictability Evaluation... The ensembles continued to have 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 tad slower (after being a bit quicker yesterday) overall with the pattern breakdown/shift including the upper low to the south of the Panhandle. For the lead system Sunday, the 12Z GFS/ECMWF/UKMET/Canadian 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 to start given the good agreement with expected differences in timing/strength that were within the ensemble spread. 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 which may yield a surface cold front south of the region. For the next Bering system, models diverged on how quickly to send the system northeastward with no clear trend the past day or two. Blended in an increased weighting of the ensemble means to account for the uncertainty. Focus for precipitation also differed along the western coastline between the GFS (a bit farther south) and the ECMWF (spread out more to the north). Blended solution was preferred. Across the North Slope, flatter flow will support a wavy boundary as a couple areas of low pressure traverse the Beaufort/Arctic but eventually weaken. ...Weather/Threats Highlights... Precipitation will be focused over western 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 these areas over a 1-2 day period with each system. Lighter precipitation will overspread parts of the North Slope/Brooks Range as well. 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. In addition, Bering systems will bring a cooling trend from west to east, with increasing coverage of below normal highs, as heights fall. On the other hand low temperatures will tend to be more above normal with only smaller areas of below normal anomalies over western areas. 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