Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 309 PM EDT Wed Oct 02 2019 Valid 12Z Sun Oct 06 2019 - 12Z Thu Oct 10 2019 Guidance continues to show a fairly amplified but progressive pattern during the period. There should be a tendency toward amplification of troughs reaching the northeastern Pacific, consistent with teleconnections relative to a strong positive height anomaly center which multi-day means have been showing near the central Aleutians. Within this pattern the first significant feature is a mainland/northeastern Pacific upper trough that may close off a low over the Gulf of Alaska around day 5 Mon and support associated surface low pressure. Guidance differences have been fairly persistent with the ECMWF/ECMWF mean slower than the GFS/GEFS mean, while other guidance has not fully committed to one side of the envelope through the 00Z/06Z cycles. The 00Z CMC/CMC mean highlight this idea, as the operational run trended closer to the ECMWF versus its prior run but the CMC mean sides with the GFS cluster. The overall progressive pattern does not particularly favor the slowest side of the spread, plus by early Mon the 00Z ECMWF is on the strong/northwest fringe of the ensemble envelope with the Gulf surface low. However with teleconnections suggesting mean troughing over the Northeast Pacific it is possible the GFS cluster could be a bit fast. Thus prefer an intermediate solution which keeps the forecast fairly close to continuity. It remains to be seen if the trend holds in successive runs, but most new 12Z guidance has generally adjusted to the faster scenario. Upstream most guidance has been fairly consistent in principle for the system which is the extratropical reflection of current Tropical Storm Mitag. The 06Z-12Z GFS/00Z ECMWF and corresponding ensemble means (plus CMC mean) cluster quite well for this system, with the only adjustment from continuity being a slightly farther south track across the northern Bering Sea. The CMC strays increasingly northward of consensus and thus could not be used in the forecast after the start of the week. Also consistent with yesterday, expect low pressure to develop over the Gulf by next Wed-Thu as the weakening parent low reaches the western mainland. Based on the above considerations today's forecast started with a compromise of 00Z/06Z operational model guidance (and a little 12Z GFS) early and then trended to a model/mean blend consisting of the 06Z-12Z GFS/00Z ECMWF and the 06Z GEFS/00Z ECMWF means. The initial Gulf system will promote a period of enhanced precipitation near the southeastern coast and Panhandle with the supporting upper trough bringing a broader area of lighter activity to locations farther west. The second system will spread moisture across the southwestern half to two-thirds of the mainland and eventually to the southeastern coast/Panhandle. 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 - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Sat-Sun, Oct 5-Oct 6. 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