Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 648 PM EST Sat Nov 30 2024 Valid 12Z Wed Dec 04 2024 - 12Z Sun Dec 08 2024 ...Wet/snowy pattern for the southern coast and Panhandle during the upcoming week... ...Overview... The average of model and ensemble guidance remains fairly consistent and agreeable with a large scale pattern evolution featuring persistent Panhandle-western Canada mean ridging aloft extending northwestward through the mainland after early Wednesday while incoming dynamics eventually elongate North Pacific-Aleutians mean upper troughing after one or more upper lows wobble around/south of the Alaska Peninsula. This pattern will favor multiple episodes of precipitation along/near southern coastal areas and the Panhandle while promoting a trend to above normal temperatures across most of the state. However individual surface lows continue to be very sensitive to lower-predictability shortwave details, so some forecast details still have low confidence. There is better consistency with the idea of the mainland staying within the gradient between these surface lows and Arctic high pressure. A larger scale mid-latitude Pacific system may approach the Alaska Peninsula by next Sunday and hopefully it will have somewhat better predictability. ...Guidance Evaluation/Preferences... As of the start of the period early Wednesday, there is at least some consistency with the idea of upper dynamics and associated surface system reaching near the Alaska Peninsula with a frontal system extending to its east. There has been a fair degree of spread and variability for the exact strength and longitude of low pressure, with latest guidance generally showing a deeper trend for the 12Z Wednesday valid time. Most dynamical and machine learning (ML) models generally show one or two more waves tracking northward to or beyond the Alaska Peninsula later in the week. While there has been some trending toward the potential for at least one of these waves to track farther west/northwest into the Bering Sea than previously forecast (including from dynamical and latest ML runs), at differing valid times the CMC and GFS lean to the more extreme side of the spread in that regard. Thus far, not enough ensemble members depict such a scenario to pull their means very far away from the Alaska Peninsula. Over the past day or so most guidance has been trending stronger with a trailing mid-latitude Pacific system forecast to track a ways south of the Aleutians Friday-Saturday. The latest majority cluster of models/means would have this system track northeastward thereafter, reaching near the Alaska Peninsula by next Sunday. ML models have exhibited some spread but the new 12Z runs seem to be clustering a little better and generally support a system in the realm of the model/mean average for track (perhaps a tad faster) with an intermediate depth between the ensemble means and deep 12Z GFS/00Z-12Z ECMWF. Through most of the period, random dynamical/ML solutions have been showing potential for additional wave development farther east of the above primary systems, with some influence on the Panhandle and vicinity. Preference continues to be to downplay the definition of these waves until guidance shows better agreement. Finally, in varying ways the 12Z GFS/UKMET in particular (CMC weaker) show potential for Arctic shortwave energy to approach the far northern mainland by around Friday. ECMWF/ICON runs and ML models are not enthusiastic about such a shortwave and the new 18Z GFS has trended noticeably northward. Today's forecast maintains the continuity of the general pattern aloft while refining some details, though the more sensitive surface low details have adjusted a little more. A blend of 00Z/12Z ECMWF runs and 12Z GFS/UKMET/CMC for about the first half of the period reflected detail refinements where some agreement existed while downplaying the more uncertain smaller-scale specifics. The forecast quickly adjusted toward a nearly even model/ensemble mean (12Z GEFS/CMCens and 00Z ECens) mix next weekend to emphasize the consensus pattern evolution and guide toward an intermediate depth of the Pacific to Alaska Peninsula system. ...Weather/Hazards Highlights... Expect continuation of multiple episodes of enhanced precipitation from the Alaska Peninsula to the Panhandle midweek into next weekend given moist southerly mean flow aloft between general troughing/upper lows over the Aleutians-North Pacific and an upper ridge over the Panhandle/western Canada through the mainland. A number of surface systems supported by features aloft should help to focus the activity. The most likely surface low tracks mid-late week should be directed toward or near the Alaska Peninsula with associated fronts extending to their east, but there is lower-probability potential for some waviness to reach farther east and affect the Panhandle (extending into the weekend). Coastal and nearby low elevations should tend to see rain, with snow elsewhere. Milder conditions over the southern Panhandle will likely yield broader coverage of rain with snow confined to higher elevations. The majority of this precipitation will remain below hazardous thresholds at most locations but higher localized totals are possible and multi-day accumulations may still end up being significant. These systems could produce periods of brisk to strong winds as well. Expect unsettled conditions but with lighter precipitation over the Aleutians through late week. A potentially vigorous Pacific system may increase precipitation and winds over the eastern Aleutians/Alaska Peninsula by next weekend, most likely Sunday. Most of the mainland north of the Alaska Range should remain dry or see only scattered light snow. The forecast transition toward multiple days of above to well above normal temperatures remains on track. Expect anomalies to increase from south to north, with North Slope locations finally flipping to above normal for next weekend after staying somewhat below normal into late week. Some valley locations where cold air typically persists longer may also take a while to trend above normal. Anomalies for min temperatures should generally a little greater than those for highs, with highest departures from normal tending to be over the south. Rausch 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