Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 646 PM EST Tue Dec 10 2019 Valid 12Z Sat Dec 14 2019 - 12Z Wed Dec 18 2019 Today's guidance offers better than average agreement/continuity in principle for two strong North Pacific/Aleutians systems during the period. The first should be over the Aleutians as of early day 4 Sat and then continue in a general eastward direction, averaging out some wobbles along the way, before dissipating after Mon. Small scale shortwaves spinning around the upper low continue to produce some uncertainty for precise details/track. The second system should follow behind by about two to three days and take a fairly similar track. GFS/ECMWF runs are signaling some degree of wave development along the leading front, and while the ensemble means are more subtle, their surface low evolutions suggest that a leading wave may ultimately become better defined than the parent low by day 8 Wed. Latest GFS/ECMWF/CMC runs maintain the parent low for a little longer than the means while the GFS is a little more concentrated than other solutions with the leading frontal wave. Farther east, most operational guidance maintains the general signal from yesterday for a northward-moving wave tracking fairly close to the Panhandle by around day 7 Tue. This continuity in the models would favor at least a defined system in the deterministic forecast even if not yet with the strength that some individual runs show. Ensemble members are sufficiently scattered to yield a mean that does not reflect this feature. Meanwhile various guidance shows opposite ideas for the upper ridge that should be just north of the mainland as of early Sat. Recent GFS/ECMWF runs have trended toward southeastward progression while the 12Z CMC/UKMET keep the ridge in the Arctic as per the ensemble means. The means have adjusted southeastward for forecasts valid Sat but still keep the ridge north of the mainland after Sat. Prefer an intermediate approach that accounts for some of the GFS/ECMWF (and day 4 mean) trends early-mid period but then reflects some persistence of the ridge over the Arctic late. Based on forecast considerations the initial blend consisted of the 00Z/12Z ECMWF and 12Z GFS/CMC early in the period followed by moderate inclusion of the 12Z GEFS/00Z ECMWF means--30 percent on day 6 Mon and 40 percent on days 7-8 Tue-Wed. One or more periods of brisk easterly low level flow may enhance precipitation over windward terrain across the northeastern Alaska Peninsula as well as Kodiak Island and Kenai Peninsula but with fairly high uncertainty for intensity at any particular time. The wave forecast to track off the Panhandle around next Tue may increase precipitation over that region. Rausch Additional 3-7 Day Hazard information can be found on the WPC medium range hazards https://www.wpc.ncep.noaa.gov/threats/threats.php Hazards: No significant hazards are expected over Alaska during this forecast period. 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