Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 658 PM EST Fri Nov 12 2021 Valid 12Z Tue Nov 16 2021 - 12Z Sat Nov 20 2021 ...Overview and Guidance Evaluation/Preferences... Shortwave troughing sliding across the Alaska Peninsula to start the period on Tuesday will interact and merge with amplified troughing dropping south across the Mainland. This will maintain troughing and a well defined surface low in the Gulf of Alaska through the remainder of next week and weekend. Elsewhere, another low pressure system will translate east well south of the Aleutians as the next deep low drops into the vicinity of the western Aleutians by late next week. This will send another deepening surface low pressure system west and south of the Aleutians Friday and Saturday. For days 4-5/Tuesday-Wednesday, the guidance shows reasonable enough agreement to allow a general deterministic model blend between the GFS, ECMWF, and CMC. After this, the models begin to diverge with the typical timing and detail differences regarding shortwave energy into the Gulf and also reinforcing energy/surface low south of the Aleutians next Friday-Saturday. The biggest model concern is the 12z ECMWF made a somewhat significant continuity jump as its much quicker to eject troughing/closed low energy across the Mainland into western Canada and tries to rebuild ridging over western Alaska by next weekend, bringing the warmer air mass in too quickly. It also presents increased differences with the next system into the Aleutians, keeping the surface low much farther north than the better consensus/ensemble means. The 12z GFS and CMC are much more in line with the ensemble means, as is the previous run (00z) ECMWF. As such, the WPC forecast used the 00z ECMWF in place of the 12z run through the entire period, with more emphasis towards the ensemble means the second half of next week to help mitigate the uncertainty. ...Weather/Hazard Highlights... Much of the precipitation over Alaska should be confined to the Aleutians/Southern Coast/Panhandle, with much of the mainland remaining dry and cold, other than maybe a few snow showers. Precipitation should accompany a cold front, spreading eastward from the Panhandle/Southern Coast to the Peninsula region on Monday into Tuesday. Southerly flow ahead of the weakening cold front into the Gulf will bring a period of moderate to locally heavy rainfall to much of the Panhandle Wednesday into Thursday, with wet but lighter intensity precipitation lingering the rest of the week associated with low pressure in the Gulf. The next system into the Aleutians should bring another round of unsettled conditions to the region with light to moderate precipitation and gusty winds for the western Aleutians and north into the Bering Sea. Below to much below normal temperatures should prevail across much of Alaska (with the exception of the North Slope region) through next week as surface high pressure becomes established across much of the state. The most pronounced anomalies should be over the western and southwestern part of the state where daytime highs could be as much as 15-30 degrees below normal. The north slope should begin above normal, but quickly moderate back closer to normal the rest of the week. Santorelli Additional 3-7 Day Hazard Information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php Hazards: - Much below normal temperatures across portions of mainland Alaska, Mon-Thu, Nov 15-Nov 18. 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