Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 739 PM EDT Sun Oct 29 2023 Valid 12Z Thu Nov 02 2023 - 12Z Mon Nov 06 2023 ...Overview... A pattern change is in store over Alaska later this week into early next week, with troughing aloft replacing short range ridging across the Interior. This will cause much above normal temperatures to reduce in magnitude and scope by late week, as a cold front tracks southward through the state. Farther south, mean low pressure at the surface and lower heights aloft will be in place across the northern Pacific. This pattern will favor some periods of precipitation across the Alaska Peninsula to Southcentral and Southeast Alaska, but nothing terribly heavy is expected. Some light snow may be possible into the Interior. ...Guidance Evaluation and Preferences... Models are agreeable that the pattern change to upper troughing will take place across the Interior, with typical differences in the details. Today's 12Z guidance suite generally has trended toward troughing/energy eroding the ridge a little earlier (around Thursday) compared to yesterday's guidance. This appears to be due to the incorporation of energy from an upper low that is currently over the Bering Sea. GFS runs string this energy out by Thursday while the ECMWF and CMC hold some of it back as a compact upper low atop eastern Siberia through Friday and toward the Bering Strait by Saturday, but some of the energy is incorporated eastward regardless. This joins vorticity that tracks from the north and the east to create the troughing pattern over the Mainland, with lowering heights through early next week. Models differ in placement of an upper low that could form over the Interior next Sunday or Monday, but within typical spread for the lead time. Farther south, a weak upper trough or low in the northern Pacific around 40N 150W at the start of the period Thursday shows some slight variations in the models with its track as it weakens, with GFS runs to the south of the ECMWF and CMC that take the shortwave into the Gulf, possibly affecting QPF distribution. A deeper and larger upper low south of the Aleutians Thursday will take over in the northern Pacific as it moves east. Some track and timing differences with that include the 12Z CMC being slower than consensus, while the GFS/ECMWF and their ensemble means seemed to be in reasonable agreement for the time frame. Thus the WPC forecast began with a blend of the deterministic models (12Z ECMWF/GFS/CMC/UKMET) for the early part of the period, and gradually increased the proportion of the GEFS and EC ensemble means with time while eliminating the CMC/UKMET. ...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. On Thursday, precipitation may be slightly enhanced across the Alaska Peninsula to Kodiak Island, with Southcentral to Southeast Alaska likely seeing greater precipitation chances into Friday. The southern coast could see additional light precipitation this weekend into early next week as well, but amounts should stay relatively low. Where precipitation occurs, the precipitation type will favor coastal/lower elevation rain and higher elevation snow. Farther north into the Interior, there may be some rounds of light snow during the period given the energy aloft and a surface frontal system passing through, but limited moisture could keep snow totals low. The milder than average temperatures in the short range are likely to continue Thursday across the Mainland, but in moderated form. Highs around 5-15F above normal are expected while lows could be 15-25F above normal. By Friday-Saturday and lasting into early next week high temperatures will flip to near to below normal, especially across the Interior. Lows on average should stay near to above normal in most areas though. The North Slope is likely to stay above average with some milder onshore flow. Meanwhile Southeast Alaska and the Aleutians look to see temperatures generally within a few degrees of 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