Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 656 PM EST Mon Jan 02 2023 Valid 12Z Fri Jan 06 2023 - 12Z Tue Jan 10 2023 ...Overview and Guidance/Predictability Assessment... Thus far the ensemble means have been fairly consistent and agreeable with the upper level pattern evolution during the period, featuring western Canada ridging that should extend into the mainland after Friday while varying proportions of energy from a trough/upper low crossing the Aleutians late this week/weekend depart north into the Bering Sea and east-southeast into the Pacific. Then a strong and large scale mid-latitude Pacific system should pass well south of the Aleutians early next week, likely with modest/minimal effects on the islands. However operational models and individual ensemble members continue to show a lot of underlying spread for important details in the forecast. These issues include northeastern Pacific waves tracking around the west side of the Canada upper ridge, various individual lows over and perhaps extending well away from the Aleutians, and by the latter half of the period the upper flow specifics over the mainland. Over the northeastern Pacific, the best defined feature of note is a system which the majority cluster says will be just west of Haida Gwaii as of early Friday and track north-northwest thereafter. Over recent runs the ECMWF/UKMET have generally been the most consistent in principle, though the 12Z ECMWF seems to become too slow given the mean flow aloft (00Z ECMWF timing more preferable). 12Z CMC specifics are a question mark but that model's evolution is reasonable as part of a multi-model composite. Latest GFS runs have been farther south and quicker to weaken the system. Based on a non-GFS scenario, expect more moisture to spread up through the Panhandle into the southeastern coast versus the GFS, but faster than the 12Z ECMWF and not extending as far west along the southern coast as the 12Z CMC. Confidence is minimal for any trailing waves, with the one notable observation being that recent GFS tracks have been bringing more moisture into Kodiak Island/Kenai Peninsula from the weekend onward versus the 12Z ECMWF/UKMET/CMC. This latter difference is somewhat connected to upper flow issues that develop over and west of the mainland, especially by the latter half of the period. Sporadic runs of various models have been taking some of the shortwave energy initially embedded within the mean southerly flow aloft and closing off a small scale upper low that could travel over or just west of the western mainland (or even form in place per the new 18Z GFS), while other runs have been trying to build some degree of ridging near the western coast of the mainland that forces a narrow trough to settle over the central mainland. Thus far the ensemble means have been remarkably consistent in showing the western Canada ridge extending back into the mainland from the weekend onward, so preference is to lean more to the consistent means until the operational models show sufficiently compelling agreement to make a significant change. Elsewhere, the ensemble means have also been consistent with the general deep-layer low crossing the Aleutians Friday-Saturday followed by a splitting of this energy (though perhaps with a slight trend to delay this split) northward into the Bering Sea and east-southeast into the Pacific. Individual model runs/ensemble members still stray widely from the mean solution with respect to where individual surface lows may be at any particular time, though at least a general model blend ends up close to the means in principle early in the period. Behind this evolution, consensus for the large and deep storm tracking across the western-central Pacific keeps it far enough south to have minimal influence on the Aleutians aside from perhaps some easterly flow on the far northern periphery. This system still requires some monitoring given typical model error that far out in time. The favored solution for the system tracking offshore the Panhandle Friday-Saturday led to starting the days 4-5 forecast with primary emphasis on the 12Z/00Z ECMWF and 12Z CMC/UKMET. Rapidly increasing detail uncertainties aloft over the mainland then led to incorporating increasing weight of the 12Z GEFS/00Z ECMWF means, 30 percent as of day 6 Sunday and 50-60 percent by days 7-8 Monday-Tuesday. The 06Z GFS run provided what minimal influence that model had in the forecast through the period, as its overall evolution at the surface and aloft compared somewhat better than the 12Z run to consensus and/or the means across the forecast domain. ...Weather/Hazards Highlights... The system currently forecast to track north-northwest from just west of Haida Gwaii early Friday onward may spread some enhanced precipitation northward through the Panhandle and then into the southeastern coast late this week into the weekend. The low may also produce at least a narrow band of enhanced winds. Precise effects on the Panhandle and vicinity will be sensitive to the exact track/strength of the system, with forecast confidence still no better than moderate. Then confidence remains well below average for any additional moisture that may reach the southern coast and vicinity, based on model spread/variability for associated surface waves as well as mainland flow details aloft. Most of the remainder of the mainland is still looking fairly dry during the period, with any low-confidence shortwaves possibly producing some light/scattered snow. The Aleutians will see an unsettled pattern from late week into the weekend in association with one or more surface lows/frontal systems that would provide a wind/precipitation focus, followed by a drier trend during the first half of next week as low pressure departs from the region. Overall above normal temperatures should prevail, with greater anomalies for lows. Readings should trend gradually cooler with time, possibly leading to some areas with slightly below normal highs over parts of the interior and southern-western mainland. Rausch 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