Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 614 PM EDT Thu Jul 16 2020 Valid 12Z Mon Jul 20 2020 - 12Z Fri Jul 24 2020 The forecast period begins on Monday with a corridor of negative mid-level height anomalies across the northern half of Alaska associated with an arctic trough draped across the region, and positive height anomalies near the southeast Panhandle region and also across eastern Siberia. The influence of the arctic trough lessens through next week as the ridge axis attempts to build in from the north Pacific. Farther to the west, a well organized low pressure system over the western Bering Sea on Monday is expected to drift slowly towards the southeast, and be over the vicinity of the western Aleutians by the end of next week, with its eastward progression limited by the ridge axis that will likely to be over the southwest Alaska mainland. The models indicate the greatest differences regarding flow across the Gulf of Alaska region, with the CMC more progressive with the initial shortwave reaching southeastern Alaska early in the forecast period, and the GFS is more progressive with the following shortwave trough. There appears to be above average model agreement regarding the well developed low pressure system near the Aleutians, with the CMC and GFS slightly ahead of the ensemble means. The ECMWF was quite strong with an arctic surface low by the end of the forecast period with little in the way of ensemble support, so it was used less for next Thursday and Friday for the northern third of the state. Elsewhere, a ECMWF/GFS/GEFS/EC mean blend was incorporated as a starting point in the forecast process for fronts and pressures. In terms of sensible weather, the best prospects for heavy rainfall will be across the southeast Panhandle region early in the week as steady onshore flow advects a plume of enhanced moisture towards the terrain, with the potential for 1 to 2+ inches through Tuesday night. The second area of noteworthy rain will be across portions of the Aleutians in association with the surface low originating from the western Bering Sea, but not to the same magnitude as the first system farther east. Temperatures will likely be below normal for the northern third of Alaska through mid-week, with the potential for some sub-freezing low temperatures north of the Brooks Range. A moderation trend is expected to commence with readings returning to near normal or slightly above for most of the state by the end of the week. Hamrick 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 the Alaska Panhandle and southern mainland Alaska, Sun-Mon, July 19-20. 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