Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 559 PM EST Fri Dec 20 2019 Valid 12Z Tue Dec 24 2019 - 12Z Sat Dec 28 2019 ...Below average temperatures expected across much of mainland Alaska through next week... ...A couple of potentially strong storms may track near the Aleutians, bringing precipitation and gusty winds... ...Wet pattern along the southeastern coast/Panhandle... The medium range period (Tues/Dec 24 - Sat/Dec 28) begins with persistent mean troughing over mainland Alaska with a surface low centered over the southern coast region and shortwave energy moving east across the Gulf/northeast Pacific. Guidance shows good agreement that the upper trough over the mainland should persist through the period, promoting an extended period of below normal temperatures the core of which should shift slowly westward with time next week. Meanwhile, energy rotating around a deep closed low over the Arctic should send a couple of cold front into the northern slope region through the period. To the south, the guidance continues to show a very active North Pacific/Aleutians stream that should include a series of shortwaves/surface lows traversing near or south of the Aleutians. Differences begin as early as day 4 with the first low moving near the Aleutians Tues/Wed. The 12z GFS and CMC are quite a bit south with this low compared to the ECMWF, with the means supporting a solution closer to the ECMWF. As the first low exits into the Gulf on Thursday, another low should again pass south of the Aleutians, with yet another low approaching the western Aleutians by day 8/Sat. It's with this second low that differences are quite significant with the 12z ECMWF bringing a rather deep low close to the islands next weekend, while the GFS is displaced several hundred miles to the southwest. The ensemble means would generally support their operational counterparts, though spread is not quite as great. This pattern supports renewed low pressure across the Gulf of Alaska and persistent focus for precipitation along the southeastern coast/Panhandle, some of which could be locally heavy at times. Depending on proximity to the Aleutians and depth of the various passing surface lows, a period of precipitation and gusty winds is possible across much of the island chain. Given the uncertainties described above, preferred a general blend of the ECMWF with the ensemble means, with significant weighting towards the means by days 7 and 8. This fits well with the preference downstream over the CONUS as well. Santorelli 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 Hazards: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Mon, Dec 23. - High winds across portions of the Aleutians, Mon, Dec 23. - High significant wave heights for coastal portions of mainland Alaska and the Aleutians, Mon, Dec 23. 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