Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 652 PM EDT Wed Jul 15 2020 Valid 12Z Sun Jul 19 2020 - 12Z Thu Jul 23 2020 The flow pattern across the North Pacific is forecast to become gradually more amplified over the weekend and into early next week, with an upper trough strengthening from the Bering Sea south across the Aleutians, and an eastern Pacific ridge approaching the Gulf region. The amplifying flow will allow for increasing potential for arctic upper-level energy to move southward, with an arctic upper low expected to affect the North Slope and portions of the Interior this weekend, and another upper low forecast to drop south across the western Bering Sea and then gradually eastward across the Aleutians through the middle of the week. The overall model and ensemble mean consensus has continued to show some improvement with the synoptic scale pattern. Similar to yesterday, the 12Z ECMWF is relatively well-clustered within the overall consensus through much of the extended forecast period. The CMC becomes more progressive with the first shortwave over the Gulf of Alaska by Day 5 (Monday) and thus becomes slightly out of phase thereafter, so it was not part of the model blend. Therefore, the ECMWF was given slightly more weighting in the model blend through Tuesday, along with some of the GFS. By the middle to end of next week, a gradual trend toward more of the GEFS and EC ensemble means was incorporated into the forecast to account for increasing uncertainty in the deterministic guidance. The primary impact of the system affecting the North Slope will be on temperatures, with readings expected to be about 10 to 20 degrees below average through Tuesday before a moderating trend commences. Portions of the Interior may also be slightly cooler than normal for this time of year. Across southern Alaska, a low pressure system will be approaching the southeastern Panhandle region and the resulting onshore flow is expected to produce enhanced rainfall from near Anchorage to the greater Juneau area, with much of this rainfall being orographically enhanced. This mainly holds true for Sunday and Monday, with less in the way of organized rainfall for later in 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, Sat-Mon, July 18-20. 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