Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 630 PM EDT Sat May 15 2021 Valid 12Z Wed May 19 2021 - 12Z Sun May 23 2021 ...Overview... Troughing is generally favored along 50N from the Aleutians to the Gulf, with weak ridging building into interior Alaska later in the week. This will maintain a fairly quiet pattern over much of the state with showers and some convection over the Alaska Range to the Brooks Range with daytime heating (50s and 60s to near 70 in the valleys) and still cool air aloft to start. More organized rainfall will be along parts of the Aleutians to Kodiak, coastal Southcentral, and eventually to the Panhandle late next week. ...Guidance/Predictability Assessment... Multiple streams in the upstream jet have complicated the pattern for several days running, with the latest 12Z guidance no exception. Best course of action has been to remain in the middle of the spread to minimize changes in the following forecast, absent any clear trends. Aside from the UKMET, the 12Z GFS/Canadian/ECMWF were clustered fairly well with the Pacific system south of the Aleutians Wed that moves eastward through the rest of the week. Weaker systems upstream have less predictability. By next Fri-Sun, GEFS mean and ECMWF ensemble mean diverge in timing, but the GFS/Canadian/ECMWF mostly stayed in between the two ensemble camps (somewhat like the 12Z Canadian ensembles, but with much more definition). Despite the uncertainty, used a majority deterministic blend to get the preferred intermediate-timing solution until next Sun when those models diverged too much. This at least maintained a reasonable system progression. ...Weather/Threats Highlights... Weak troughing over the mainland will promote scattered showers (snow over higher elevations) across the Interior/North Slope through much of the week, with isolated convection as temperatures aloft remain cool (850T near 0C to start). A more defined system around the Aleutians on Wednesday will bring generally light to perhaps 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. Temperatures will be within several degrees of normal over much of the state, warming into next weekend over the Interior to near 70, 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