Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 547 PM EDT Sun Oct 18 2020 Valid 12Z Thu Oct 22 2020 - 12Z Mon Oct 26 2020 ...Heavy rain possible for portions of coastal Southcentral later this week into the weekend... ...Guidance/Predictability Assessment... A robust Pacific system is forecast to lift across the Aleutians late Thu into Fri as upper ridging over the Interior moves eastward and weakens. The upper pattern is forecast to trend toward a flatter flow as another system enters the far western Bering by the end of the period. The 12Z GFS/ECMWF formed a good cluster with the 12Z GEFS mean and 00Z ECMWF ensemble mean for most of the period, with a trend toward a bit quicker and farther west track of the Aleutian/Bering parent low, but maybe a bit slower progression with the attendant surface front and possible surface wave (or two) development. With increased ridging over the northeastern Pacific (as opposed to farther north), the front may have a hard time progressing eastward through the Gulf. The 12Z Canadian/UKMET again were a bit displaced from the GFS/ECMWF out of the short term and were not used. By next Sun/Mon, triple point low should take over in the Gulf near Kodiak as the front slowly moves eastward. The next system should enter the western Bering and a blended solution sufficed at this lead time. ...Weather/Threats Highlights.. Upper ridging will bring above normal temperatures to much of western coastal Alaska and the Interior, especially over the North Slope, with dry conditions along the Arctic coast. Temperatures may be 10-15 degrees above normal along and north of the Brooks Range, and 5-15 degrees above normal north and west of the Alaska Range. Areas of eastern/southeastern Alaska and especially the Panhandle will see near to below normal temperatures as high pressure (around 1045mb) delivers easterly flow to the region Thu-Sat. Temperatures will moderate just a bit next Sun-Mon across the Panhandle as onshore flow picks up. Rainfall around the Aleutians system could be locally heavy over the AKPen and Kodiak (southeast-facing areas) Thu-Sat as the weakening lead system and more dominant Aleutian system lift northeastward. Some modest to perhaps heavier rain could move eastward toward southeastern coastal areas as the warm front lifts toward the coast. It will be rather breezy/windy over the southern Bering and Aleutians (30-40kts) due to the tightening pressure gradient between mainland high pressure and the low pressure system around 980mb. Fracasso 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