Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 448 PM EST Mon Jan 20 2025 Valid 12Z Fri Jan 24 2025 - 12Z Tue Jan 28 2025 ...Heavy precipitation across portions of southeast Alaska and the Alaska Panhandle at times into early next week... ...Heavy snow expected across the Brooks and Alaska Ranges as well as the Seward Peninsula late this week... ...Storm-force winds for the upper Aleutians and lower Alaska Peninsula Thursday... ...Sharply colder early next week... ...General Overview with Model Guidance Assessment... The general flow pattern features an approaching upper trough trying to move into AK and shift ridging into southeastern AK and northwest Canada. This should maintain periods of enhanced onshore flow across southeast AK and the AK Panhandle over the next week or so, keeping them wet. Issues have become more significant today, which is increasing the reliance on the 12z NAEFS and 00z ECMWF ensemble mean solutions -- differences arise by the increasing wavelength/broadness of upper level systems in the northern stream of the Westerlies/Arctic and whether or not that means the flow should be zonal sooner rather than later across southernmost AK, including the Aleutians. With the ensemble means showing more amplification that some of the deterministic guidance, this also led to lesser deterministic weight. The pressures, winds, 500 hPa heights, fronts, PoPs, and QPF were initially based on the 12z runs of the UKMET, Canadian, GFS, and ECMWF, with 60% of the solution composed of 12z NAEFS/00z ECMWF ensemble mean early next week to deal with issues. The remainder of the grids were based more towards the 19z NBM. This forecast philosophy was able to maintain a decent amount of continuity, with the main aspects being a more southern system south of AK and some slowing to the arctic air intrusion into AK. ...Weather/Hazards Highlights... The main story will be the periods of heavy precipitation across southeast AK and the AK Panhandle over the next week or so, with local amounts in the 4-8" range forecast this weekend into early next week. As a deep cyclone (~980s hPa central pressure) moves through the Bering Sea and a surface high strengthens well south of AK (~mid 1040s hPa central pressure, which is about three sigmas above the mean or near record territory for the northeast Pacific), a period of storm-force winds appears likely across the upper Aleutians, southern portion of the AK Peninsula, and the southwest AK coast on Thursday into very early Friday. As the upper trough slowly edges into western AK, a prolonged period of moderate to heavy snow is possible late this week across portions of the Seward Peninsula and Brooks Range; model spread here has grown some since this time yesterday, with the preference becoming somewhat wetter. From late week into early this weekend, heavy snow is expected across the Alaska Range. The state will dry out as arctic air invades early next week. Due to the general amplified pattern over North America (ridge western continent and trough eastern continent), temperatures will start well above average across the state, with 20-40F warm anomalies common for the west & north with 15-30F positive anomalies common in eastern AK and the AK Panhandle early on/late week. The warm anomalies initially erode slowly in the wake of the Pacific frontal passage, down to roughly 10-20F this weekend, but then drop sharply in the wake of the Arctic/secondary front Sunday onward which has a ~1046 hPa high pressure cell in its wake across eastern Siberia. Lows are expected fall towards -40F in spots next Tuesday night. Roth 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