Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 734 PM EDT Tue Sep 21 2021 Valid 12Z Sat Sep 25 2021 - 12Z Wed Sep 29 2021 ...Guidance and Predictability Assessment... The Alaska pattern in the medium range period will be generally characterized by an upper low drifting from the Arctic Circle southward to northwest of the state, while spokes of upper troughing pass across the state. At the surface, after a potent low causes heavy precipitation across the Panhandle during the short range period, another surface low is forecast to track across the northeastern Pacific and cause another round of precipitation for the Panhandle early next week. Then, another low that could be reasonably deep for this time of year is currently expected to move from the Bering Sea southeastward across the Aleutians into the Gulf of Alaska, which could cause increasing precipitation chances for southern Alaska and the Panhandle dependent on the low track. Model guidance was generally agreeable with this overall pattern, but with differences in timing and depth of some features. However, today's 12Z guidance is quite consistent with a track of this weekend/early next week's surface low remaining fairly far south of Alaska until it approaches the Panhandle around Monday. This has led to a southern shift in the low track compared to yesterday's forecast, which reduces sensible weather impacts across the Aleutians to Southcentral Alaska, though heavy precipitation is still likely in the Panhandle. But model guidance diverges upstream in the Bering Sea, with mid/upper-level shortwave placement and evolution and thus the surface low positions. Around Sunday/Monday, the 12Z GFS/UKMET/CMC split from the 12Z EC/06Z GFS, with the former group having a faster shortwave and surface low track through the Bering Sea and across the Aleutians. WPC leaned more toward the slower solutions given the GEFS and EC means were slower as well, suggesting this was the safer camp to choose at this point. After that, regardless of exactly how the vort maxes evolve and combine, even the deterministic models converge somewhat well on troughing redeveloping centered over the Gulf by midweek. Overall the WPC forecast used a model blend of the 12Z EC/GEFS mean/EC mean, along with a small portion of the 06Z GFS early in the period, and favored the means more as time progressed. ...Sensible Weather... After a wet short range period, with some precipitation lingering into the weekend, the Panhandle is forecast to get another round of precipitation early next week given the approaching strong low, while gusty winds are expected offshore. Farther north, central/eastern parts of the mainland could see moisture and increased precipitation (some falling as snow) chances this weekend. Then the next potentially strong low pressure system could bring gusty winds and precipitation to the Aleutians and toward Southcentral Alaska and eventually the Panhandle again by midweek, though uncertainty remains in the low's track and strength. The upper trough persisting over the mainland will keep temperatures below normal over much of the state. Coldest anomalies should be over the southern parts of the state and across higher elevations of the Brooks and Alaska Ranges. High temperatures should range from the 40s and 50s in coastal areas, while highs could remain in the 30s or lower across much of the mainland. Tate Hazards: - Heavy precipitation across portions of coastal and higher terrain of southern Alaska into the Alaska Panhandle, Fri, Sep 24. - Heavy rain across southern portion of the Alaska Panhandle, Fri, Sep 24 and Mon-Tue, Sep 27-28. 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