Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 659 PM EDT Sat Apr 17 2021 Valid 12Z Wed Apr 21 2021 - 12Z Sun Apr 25 2021 ...Overview and Guidance/Uncertainty Assessment... Latest guidance continues to depict a fairly blocky regime during the extended range period. This pattern will be highlighted by upper ridging that covers most of the mainland into the western Bering Sea/eastern Siberia, while a consolidating Pacific mean low aloft should settle into a position south of the eastern Aleutians and Alaska Peninsula. Shortwave energy within progressive flow around the north side of the upper ridge may push a cold front/lower heights into the northern/eastern mainland through Thursday. Towards the end of the period, another upper low should move towards/south of the Aleutians underneath the mainland ridge which should also help shift the Gulf low eastward as well. Most of the state should be fairly dry for most of next week and into the weekend, with the best potential for precipitation along parts of the Eastern Aleutians and Peninsula. Most of the guidance does agree that upper ridging in some form should dominate over mainland Alaska (and sliding westward into the Bering) through the period. It is south of the Aleutians and into the Gulf where models begin to diverge fairly rapidly after day 5. The 12z GFS maintains a more blocky looking pattern (with some support from the 12z CMC) with a defined ridge in between the two upper lows mentioned above. The 12z ECMWF drags that north Pacific/Gulf low more westward with time with lower heights/broad elongated troughing south of the state which should act to break down the ridge more than the GFS would try to indicate. Both of the GEFS/ECENS means would support maintaining the blocky pattern so after day 5, the WPC blend trended quickly in favor of the ensemble means and the GFS. This approach fits well with yesterdays WPC continuity as well. ...Weather/Hazards Highlights... Most precipitation should be confined to the Aleutians/Alaska Peninsula and vicinity Wednesday and Thursday, with a fairly persistent flow of moisture carried in the gradient between one or more Pacific lows and high pressure well to the north. Light to moderate amounts are most likely but some locally higher totals could be possible depending on exact strength and track of Pacific systems. The rest of the mainland should remain dry throughout the entire week and into the weekend. The vast majority of the state should be well above normal in terms of temperatures through much of the period, with the warmest anomalies over the North Slope region and western areas of the Mainland (with even more anomalous warm morning lows). Lowering heights across Alaska next weekend should help to moderate temperatures a bit, especially for eastern areas. The exception to all this warmth will be in the southeast quadrant and much of the Panhandle temperatures should be near or below normal the entire medium range period. Santorelli 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