Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 651 PM EDT Sun May 16 2021 Valid 12Z Thu May 20 2021 - 12Z Mon May 24 2021 ...Overview... Troughing near the Aleutians late this week will translate eastward into the Gulf and weaken as ridging builds to its north into the Interior. A new system will dig into the Bering Sea this coming weekend into next week. This promotes an unsettled pattern over the southern coastal areas with more scattered showers and convection north of the Alaska Range. Temperatures will trend warmer over interior areas as heights build. ...Guidance/Predictability Assessment... The deterministic models appear to be slowly coming into better agreement as the pattern becomes a bit more defined. However, the 12Z UKMET/Canadian diverged rather quickly from the consensus of the 12Z GFS/ECMWF/GEFS mean/Canadian mean and 00Z ECMWF ensemble mean. Though agreement was not tightly-clustered, that grouping fared quite well into next weekend with the system just south of the Aleutians Thu-Fri (ECMWF on the northern side) and the incoming system(s) into the Bering next weekend (broadly speaking). With upstream ridging forecast to build to +2 sigma in the ECMWF ensemble mean over the Sakhalin Oblast next Sun/Mon, the robust solutions of the ECMWF/GFS seems plausible. However, given the inconsistent recent runs even in the ensembles, trended toward a deterministic/ensemble split and then tilt toward an ensemble consensus by the end of the period. ...Weather/Threats Highlights... Weak troughing over the mainland will promote scattered showers (snow over higher elevations) across the Interior/North Slope for the first part of the forecast, with isolated convection as temperatures aloft remain cool (850T near 0C to start). A defined system around the Aleutians on Thursday will bring widespread light to modest rain for the island chain as the occlusion skirts eastward. Enough moisture could get drawn northward toward Kodiak and the southern/coastal area of Southcentral to bring a couple inches of rain to those areas with southern exposure. Temperatures will be within several degrees of normal over much of the state, warming into next weekend over the Interior to near 70F, but near to below normal along coastal areas of the Gulf where clouds/rain are more likely. 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