Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 641 PM EDT Fri Apr 16 2021 Valid 12Z Tue Apr 20 2021 - 12Z Sat Apr 24 2021 ...Overview and Guidance/Uncertainty Assessment... Latest guidance continues to depict a 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 by Tuesday-Thursday. Most of the state should be fairly dry for most of next week, with the best potential for precipitation along coastal locations shifting west to east from the Aleutians to Southern Coast to Panhandle. Overall, the 12z GFS and 12z ECMWF and respective ensemble means shows fairly good agreement on the large scale through much of the period and continues to trend towards a stronger ridge aloft. The 12z CMC (along with the 00z ECMWF) was the outlier with bringing stronger shortwave energy into the Bering Sea by mid-week and faster to break down the ridge. The 12z ECMWF came in much closer to that of the GFS, which advertise being less aggressive to break down the ridge across the mainland/Bering/eastern Siberia and suppressing energy/low pressure systems south of the Aleutians. Models do show pretty good agreement with lowering heights into northern/eastern Mainland early to mid week as well. The WPC blend favored the deterministic guidance (GFS/ECMWF) for the first half of the period. After this, increased influence from the ensemble means to account for some smaller scale timing and detail differences. Leaned a little heavier towards the 12z GFS over the 12z ECMWF just given the GFS has been the most consistent with showing the stronger ridge and is the deterministic solution which best supports the ensemble means. 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, 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. By the end of the week, lighter precip may begin shifting east towards the Southern Coast region and the Panhandle. The rest of the mainland should remain dry throughout the entire week. A vast majority of the state should see above normal temperatures at the start of the period Tuesday, with the warmest anomalies over the North Slope region and western half of the Mainland (with even more anomalous warm morning lows). A cold front should deliver a near or even slightly below normal air mass during the middle of next week to parts of the eastern Mainland and especially the southeast and Panhandle. Temperatures may also begin to moderate a bit across the rest of the state by next weekend. 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