Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 652 PM EDT Mon May 17 2021 Valid 12Z Fri May 21 2021 - 12Z Tue May 25 2021 ...Overview... Messy multi-stream flow off Asia in the short term will transition toward a bit more definition in the medium range as a Gulf and then Bering system traverse the region. With upper ridging forecast to build across the Sakhalin Oblast on Sunday, downstream troughing will dig through the Bering and ridging over the Interior. This favors a warm-up across the Tanana Valley with rainfall focused over southern/coastal areas of Southcentral this weekend and the Aleutians to southwestern Alaska by next week. ...Guidance/Predictability Assessment... The ensemble systems (GEFS/Canadian/ECMWF) showed good agreement through the period even as the deterministic models continued to stray from their consensus and relatively good continuity. The 12Z GFS was well-removed from the consensus even before the forecast period (Thu) over the Bering as it took a defined system southeastward toward Bristol Bay -- much stronger and farther south than the other guidance or previous runs. Followed the forecast cluster of the ECMWF/UKMET/Canadian to start before the Canadian took the southern stream Pacific system northward to the Bering rather than allowing it to meander south of 50N. The 12Z ECMWF offered a most reasonable depiction of the systems progressions until next Sun-Mon where it developed a low in the southern stream toward the Aleutians. Given its low predictability, opted to rely solely on the ensemble means (12Z GEFS mean was best defined) and a simple occluded system in the Bering early next week until the upstream pattern comes into better focus. ...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). A defined system just south of the AKPen on Friday will bring widespread light to modest rain for the eastern Aleutians into southwestern Alaska 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. Lighter rain is expected for the Panhandle as the system progresses steadily eastward late Saturday. Next system in the Bering could bring more light rain to the Aleutians early next week and perhaps into the western mainland thereafter. Temperatures will be within several degrees of normal over much of the state, warming into the weekend over the Interior to the 60s and 70s (10-20 deg above normal), but near to below normal along coastal areas of the Gulf where clouds/rain are more likely. Fracasso Hazards: No significant hazards are expected over Alaska during this forecast period. 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