Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 646 PM EDT Fri Jul 17 2020 Valid 12Z Tue Jul 21 2020 - 12Z Sat Jul 25 2020 The forecast period begins on Tuesday with negative mid-level height anomalies across northeastern Alaska associated with an arctic upper low and trough situated northwest of the state, and positive height anomalies over the Aleutians and also across eastern Siberia. The influence of the arctic trough briefly lessens into the middle of next week as the ridge axis attempts to build in from the north Pacific across western Alaska. By the end of the forecast period next weekend, it is appearing increasing likely that another potent arctic trough will affect the northern half of the state and heralding a potential pattern change. Farther to the west, a well organized low pressure system over the western Bering Sea on Tuesday is expected to drift slowly towards the east and just north of the Aleutians through Friday. The models indicate relatively good model agreement on Tuesday with the exception of the CMC, which is more progressive with the initial shortwave reaching southeastern Alaska early in the forecast period. There appears to be above average model agreement regarding the well developed low pressure system near the Aleutians, with the GFS the most progressive solution. Similar to yesterday, the ECMWF was quite strong with the arctic surface low by the end of the forecast period, so it was used less for the Thursday through Saturday period 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, along with some UKMET through Wednesday. In terms of sensible weather, the best prospects for heavy rainfall will be across the southeast Panhandle region on Tuesday 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 for much of the week, with the potential for some sub-freezing low temperatures north of the Brooks Range. 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, Monday, July 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