Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 333 PM EDT Sat Oct 19 2019 Valid 12Z Wed Oct 23 2019 - 12Z Sun Oct 27 2019 The extended forecast for Alaska continues to highlight two strong storm systems, the first one most likely near the Alaska Peninsula at the start of the period early day 4 Wed and the second tracking into the Aleutians during the latter half of the week. Both systems will bring the potential for areas of heavy precipitation with locations from the Alaska Peninsula to the Panhandle seeing highest 5-day totals. Expect strong winds and high waves to accompany these systems as well. For the leading system near the Alaska Peninsula to start the period, guidance continues to show meaningful track and timing differences but with a slow tendency toward convergence. One favorable trend is that today more ECMWF ensemble members are showing a strong surface low near the Peninsula than 24 hours ago, helping its ensemble mean to be somewhat deeper--but likely still excessively weak. Fewer ECMWF members have a suppressed wave that would miss the Peninsula/Gulf of Alaska. Consensus of latest operational guidance is providing increased confidence that the central pressure should reach at least into the 970's mb while 12Z runs in particular are adding to potential for the upper half of the 960's--still not quite as deep as GFS runs. The GFS through the 12Z cycle is still a bit on the western side of the spread (albeit supported by GEFS means thus far), while the 12Z UKMET/ECMWF are positioned between the GFS and farther east CMC. The new ECMWF represents a fractional westward shift from its 00Z run. Based on guidance behavior thus far and data available through arrival of the 12Z GFS, an intermediate solution among the 06-12Z GFS and 00Z ECMWF/UKMET seemed to be the best way to guide the forecast. The system should rapidly weaken over the following couple of days. The front trailing from this storm will extend into the northeastern Pacific and possibly contain a wave that could have some influence on the Panhandle during the latter half of the week. Guidance shows a wide spread for this wave. Among 12Z solutions the UKMET is deepest/farthest northwest while the GFS is next closest (was the farthest northwest before the UKMET's arrival). Other solutions are weaker and/or southeastward, while ensemble spread is sufficient for the means to be fairly ill-defined. Predictability is low due to the feature's small scale and sensitivity to finer details of shortwave impulse(s) aloft. Over the past day guidance clustering has dramatically improved for the depiction of deep low pressure reaching the Aleutians by Thu-Fri and then weakening gradually as it tracks into the eastern Aleutians/Bering Sea next weekend. A significant part of this improved agreement relates to the resolution of how recurving Typhoon Neoguri interacts with mid-latitude dynamics. Over recent days the ECMWF mean, and with varied details operational runs, have provided the best signal for a significant storm while it took until the past 12 hours or so for the GEFS/CMC means to come around to this idea. Guidance generally agrees upon a weakness aloft near/north of the northern coast of the mainland mid-late week. This weakness should be pushed northward next weekend as the deep Aleutians storm helps to build a downstream ridge aloft into the mainland. A blend among the 06-12Z GFS/00Z ECMWF (plus the 00Z UKMET through day 5 Thu) provided the best operational template for today's forecast. A small amount of the 00Z ECMWF mean (deeper than the GEFS for extratropical Neoguri) was incorporated by Fri. Increasing spread of operational runs led to increasing the ensemble weight to 40-50 percent on day 8 Sun. Rausch Additional 3-7 Day Hazard information can be found on the WPC medium range hazards 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