Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 751 PM EDT Fri Oct 27 2023 Valid 12Z Tue Oct 31 2023 - 12Z Sat Nov 04 2023 ...Overview... Upper ridging will be in place across much of the state as the medium range period begins Tuesday, which could finally get repressed by late next week, while mean troughing extends across the Bering and into the northern Pacific. Much above normal temperatures will be in place early in the week under the ridge, with gradual moderation towards normal as next week progresses. The pattern will favor some periods of precipitation across the Alaska Peninsula to Southcentral Alaska and eventually Southeast Alaska, but nothing terribly heavy is expected. ...Guidance Evaluation and Preferences... Model guidance is in reasonable agreement during the early part of the medium range period. On Tuesday models indicate three distinct upper lows--one over the northern Pacific south of the Alaska Peninsula, one over eastern Siberia, and one over the Bering Sea/western Aleutians. The northern Pacific low looks to track east and weaken, the eastern Siberia one could continue tracking northwest, but the Bering Sea may be the most impactful one to the pattern as it moves east and then southeast for the latter part of the week into the northern Pacific. Models vary in some of the details with typically increasing spread with increasing lead time, but did not see anything considered an outlier in today's 12Z guidance. Meanwhile models continue to show some variations with how the northern side of the ridge may erode. Guidance is generally holding onto higher 500mb heights through around Thursday compared to yesterday's guidance, with less energy suppressing it and possibly a slower surface front tracking across the Interior. But by late week a mid-upper trough may take over. The CMC and ECMWF broke energy away from an Arctic trough to the east to erode the ridge, while in the 12Z GFS it arose from energy dropping from north to south. Regardless the upper-level pattern looks to change somehow by late week. For the WPC forecast, a blend of the deterministic models (the 06Z/12Z GFS and 12Z ECMWF/CMC/UKMET) was used for the early part of the period. Gradually increased the proportion of the GEFS and EC ensemble means with time to over half by Days 7-8 amid increasing forecast spread. ...Weather and Hazards Highlights... Precipitation across the state should be generally light to moderate through the period, and timing of the precipitation will depend on the details of upper and surface low positions particularly in the northern Pacific. The pattern should cause most precipitation to be limited to the southern coast, from the Alaska Peninsula into Kodiak Island and the Kenai Peninsula and Southcentral Alaska, and by Thursday-Friday some precipitation could sneak into Southeast Alaska with the eroding ridge. Additionally, some precipitation may affect the western Mainland through Tuesday with a cold front coming into the region. Where precipitation occurs, the precipitation type will favor coastal/lower elevation rain and interior/higher elevation snow. Much of the state will see above normal temperatures at least through around Thursday, if not beyond. The greatest anomalies will be across the North Slope and northwestern Mainland through midweek, with lows 20-30F or more above average and highs more along the lines of 10-25F above normal. As the upper ridge gets suppressed later next week and a cold front pushes through, temperatures are likely to moderate closer to normal, but remain above average except perhaps in the eastern Interior. Meanwhile Southeast Alaska and the Aleutians look to see temperatures generally within a few degrees of average. Tate 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 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