Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 649 PM EDT Mon Oct 02 2023 Valid 12Z Fri Oct 06 2023 - 12Z Tue Oct 10 2023 ...Multi-day heavy precipitation threat from southern to Southeast Alaska along with windy conditions and freezing rain and snow potential for Southwest Alaska and the Alaska Range into the Interior... ...Overview... It generally remains the case that guidance continues to show an evolving pattern that should favor a period of heavier precipitation across southern portions of the state including the Panhandle, especially late this week that will linger into the weekend and potentially resurge again early next week. Models and ensembles develop a slow-moving trough/upper low over from the southwestern mainland to the northwestern Gulf of Alaska by Friday. A downstream mean ridge should extend into the southeastern mainland from the Panhandle and western Canada. This should favor a primary surge of moisture up to the state late this week, while details of one or more trailing Northeast Pacific lows and associated precipitation coverage and amounts less certain thereafter with their northward swing associated with uncertain interaction with more northern stream energy digging. A primary feature of interest to the north will be an upper trough extending into the mainland from an Arctic Ocean upper low, with some debate over its progression and the extent and timing of the digging of shortwaves southward to periodically amplify unsettling flow. ...Guidance Evaluation and Preferences... Model and ensemble solutions now offer lower than normal forecast spread through medium range time scales, bolstering forecast confidence to a degree. A preferred composite of best clustered guidance from the 12 UTC GFS/ECMWF/Canadian models and the GEFS/ECMWF ensemble means seems to offer a good forecast basis for a mid-larger scale system and pattern evolution with seemingly average to better predictability and continuity. Manual adjustments applied to the composite will re-deepen best organized systems as consistent with individual predictability as an offset to the inherent weakening as per the blending process. ...Weather and Hazards Highlights... With relatively greater confidence than the remainder of the forecast, expect a strong surge of long fetch lower lattitude moisture/atmospheric river later this week into the weekend into Southeast Alaska as a warm front lifts through the Gulf of Alaska in advance of a deepened Gulf system. This moisture should produce heavy rainfall and mountain snows from the Panhandle back to portions of the southern coast. Details for additional potential systems reaching the Gulf of Alaska become more uncertain over the weekend into next week, but there is a growing signal showing a subsequent deep low approach up from the eastern Pacific into early next week as a maritime threat and as a focus for onshore activity. Confidence decreases with respect to precipitation coverage and amounts, but the overall pattern seems to offer a continued potential for enhanced rainfall and mountain snows extending across the broad southern mainland tier, including Southcentral and the Alaska Range as well as the Panhandle. Lingering cold temperatures may pose a threat for impactful freezing rain into Southwest Alaska for the Lower Kuskokwim and vicinity and across the southern Interior including the Copper River Basin, with snow over other areas. For the five-day period, the highest precipitation totals will likely be over the Southeast. Between low pressure over and east of the Alaska Peninsula and high pressure forecast over or north of the North Slope, a broad area of the mainland into the eastern Bering Sea should have a fairly tight gradient supportive of brisk to strong winds and gaps winds to monitor. Schichtel Hazards: - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Thu-Sat, Oct 5-Oct 7. - Heavy rain across portions of the Alaska Panhandle, Mon, Oct 9. 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