Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 339 PM EDT Sun Mar 24 2019 Valid 12Z Thu Mar 28 2019 - 12Z Mon Apr 01 2019 Over the mainland and vicinity there is still a lot of spread among individual models and ensemble members for what will happen to shortwave energy that should cross the mainland late this week behind an upper high that continues its southeastward path beyond the Panhandle, and then for the upper ridge/high that builds behind this shortwave. On the positive side there is somewhat more clustering in principle than yesterday--so forecast confidence is a bit higher than yesterday's minimal level but remains in the lower half of the spectrum. The most common theme in today's guidance is that the shortwave initially approaching the mainland should end up being faster and less amplified than depicted in the 00Z ECMWF. During the first part of the forecast the ECMWF mean has a more subdued reflection of this idea but then steadily trends closer to the other ensemble means which have been showing stronger ridging aloft over the mainland. By Sun the 00Z ECMWF mean trend reflects a southeastward adjustment of the upper high from over/north of the Bering Strait into the mainland. Interestingly this is back to what the ECMWF mean was advertising three cycles ago in the 12Z/22 run. Also of note, 24-hour adjustments in ECMWF/CMC-based model and ensemble guidance have backed off from their idea of east-central Pacific low pressure and moisture making their way into the northeastern Pacific/Gulf of Alaska. D+5 through D+8 multi-day means have been showing a strong core of positive height anomalies shifting from the southern coast near the Kenai Peninsula to along the western coast of the mainland. Teleconnections support the latest non-ECMWF consensus of fairly high heights over the mainland along with an upper weakness to the south likely not reaching much farther north than 50N latitude. Among remaining guidance, the 06-12Z GFS are somewhat slower than the 00Z GFS/UKMET/CMC and 06Z FV3 GFS with the shortwave of interest but within the realm of possibility. Another positive trend is that latest GFS runs have really dampened out an upstream shortwave which earlier runs had brought to the mainland by Fri. This feature was not well supported by most other solutions. Over the North Pacific/Aleutians/Bering Sea, there is general consensus that strong flow ahead of a mean upper low centered near Kamchatka should propel multiple western Pacific frontal systems into the western half of the Aleutians/Bering Sea from late this week into the weekend. Each front (possibly anchored by or including a better defined low than in manual progs) may be accompanied by fairly strong winds. Between the weekend and early next week guidance suggests that east-west oriented troughing aloft will expand across most of the North Pacific with one or more low centers tracking south of the Aleutians. A blend weighted 2/3 toward operational models early and more toward the ensemble means mid-late period represents consensus well while accounting for the wide spread of individual models/ensemble members for individual surface low centers. Based on preferences over the mainland and vicinity, today's forecast blend used 30-35 percent of the 00Z ECMWF mean as the only ECMWF-based guidance. Operational model components included the 12Z GFS/06Z FV3 GFS along with the 00Z CMC (into day 7 Sun) and 00Z UKMET (into day 5), while the 06Z GEFS/00Z NAEFS means contributed input from about mid-period onward. Ensemble means comprised 70-80 percent of the blend by days 7-8 Sun-Mon. Rausch Bullet points from the WPC Days 3-7 Hazards chart can be found 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