Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 752 PM EDT Sun Oct 24 2021 Valid 12Z Thu Oct 28 2021 - 12Z Mon Nov 01 2021 ...Overview and Guidance/Predictability Assessment... The medium range forecast over Alaska shows a persistent pattern with an upper low initially centered northwest of the state and drifting west and south with time, while rounds of troughing track around it. One such shortwave trough is forecast to push across the Alaska Peninsula Thu and into the Gulf of Alaska Fri, before deeper troughing establishes itself south of the Aleutians in the northeast Pacific on Friday and tracks slowly eastward over the weekend. Today's 12Z model guidance (including the GFS/ECMWF/UKMET/CMC) is more agreeable with this second trough and its associated surface low, but with minor differences typical of the forecast time frame. Despite the differences being relatively small, small variations in the low track closer to or farther from the Southcentral Alaskan coast could impact the start time and amounts of heavy precipitation there. Overall a mainly deterministic model blend worked for about days 4-6. Farther upstream, model agreement starts to go somewhat awry as energy from a possibly closed upper low moves east across eastern Russia and may combine with energy from what is currently T.D. Twenty-Five-W before tracking south of the Aleutians in the north Pacific. This evolution is rather uncertain, which can also be seen by ensemble mean guidance blending everything out to barely show upper-level and surface features there. The UKMET seems to be the first to diverge from consensus and was removed from the blend after day 5. Confidence is low with these features with plenty of run-to-run differences in guidance and considerable variability in ensemble guidance, but luckily the 12Z GFS and ECMWF were not terribly different, so for days 7-8 ended up with a basically even blend of the GFS/GEFS mean/EC/EC mean showing additional low pressure tracking into the north Pacific. ...Weather/Hazard Highlights... Light to moderate precipitation is forecast for southern parts of Alaska Thursday, as a relatively weak low pressure system tracks near Southcentral Alaska and convergent flow continues across the Panhandle. Precipitation will likely ramp up considerably for the Alaska Peninsula into Southcentral Alaska possibly by Friday but especially into the weekend, as a deeper low pressure system spins over the Northeast Pacific/Gulf of Alaska. Gusty southerly winds are also possible there, while gusty northerly winds are expected on the backside of the low for the Aleutians. Meanwhile, generally quiet conditions are expected for much of mainland Alaska, with occasional snow showers over the western mainland through late in the workweek, and snow chances should increase for western and central parts of the mainland over the weekend with the moist onshore flow from the low pressure system. Temperatures across much of interior Alaska will be near to slightly above normal through the end of the week, while colder than average temperatures especially in terms of highs are forecast over southwestern Alaska into the Panhandle. By early next week, temperatures could gradually warm as heights aloft rise as the mean upper low shifts away from the state. Low temperatures are currently expected to be 10-25F above normal for much of the interior, with highs 5-15F above average. Tate 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 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