Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 253 PM EST Thu Nov 07 2019 Valid 12Z Mon Nov 11 2019 - 12Z Fri Nov 15 2019 The best clustering of guidance shows strong height falls progressing across the North Pacific and Aleutians early-mid week, supporting a potentially strong storm for which the full range of guidance has been very diverse for precise strength and track. This energy/storm system will help to push leading northeast Pacific/Gulf of Alaska shortwave energy into the long-term mean ridge aligned over the British Columbia coast and Alaska Panhandle. Meanwhile expect an upper high to close off northwest of the mainland while cyclonic flow develops to farther east and including the northern mainland. Later in the period details become murky within the general col region depicted over parts of the mainland/eastern Bering Sea. Finally, a progressive system should track into the western-central Pacific over the course of the week. Over the past day guidance has been trying to converge toward a common solution for northeastern Pacific/Gulf of Alaska low pressure during the first half of the week. In particular GFS runs have trended eastward while the ECMWF has adjusted farther north. The best clustering of ensemble members would favor a track closest to the 12Z GFS/00Z ECMWF. However latest CMC/UKMET runs and some GEFS/ECMWF ensemble members still offer potential for a more southern track, associated with stronger energy aloft. Prefer the GFS/ECMWF cluster given that stronger/southern solutions may not be ideal for a feature heading into a mean ridge. The 12Z ECMWF has come in similar to its previous run. Arrival of the new 12Z guidance seems to be adding some clarity to the deep storm system that may develop over the North Pacific and possibly reach the eastern Aleutians and/or Alaska Peninsula. Some GFS runs had stayed from consensus in tracking the storm well northwest into/through the Bering Sea but have been consistent with depicting a very strong system. Other models have varied more in strength but at least would keep the storm farther southeast. The new 12Z GFS fell in line quite well with the ensemble means (which have adjusted southeastward some from yesterday), favoring a 12Z GFS/00Z ECMWF and 06Z GEFS/00Z ECMWF mean compromise as a reasonable starting point. The 12Z UKMET/CMC have come in with a very deep system along a similar path, so now there is somewhat more confidence in going with a deeper system. The new ECMWF is also quite deep though a bit east of the majority into Wed. The general signal for the upstream western-central Pacific system has good continuity. However over the past day most models and ensemble means have made a pronounced southward shift in dynamic focus/low pressure, with less influence on the western Aleutians than forecast by the 12Z GFS. With time, confidence decreases in specifics of flow aloft over the mainland as a weakness develops southeast of the closed upper high north of eastern Siberia. The most common idea shared by latest model/ensemble guidance is for some energy within the cyclonic flow over the northeastern mainland to begin stretching southwestward late in the week. Fortunately the surface pattern continues to exhibit strong clustering regardless of specifics aloft, with a front dropping south over the mainland while the surface gradient strengthens between high pressure over the Arctic and low pressure near the Alaska Peninsula. Based on the above preferences through arrival of the 12Z GFS, the forecast blend started with the 12Z GFS/00Z ECMWF and 06Z GEFS/00Z ECMWF means through the period. 70 percent weight went to the operational runs early-mid week followed by a trend to 50/50 model/mean weight. The northeastern Pacific/Gulf system will bring the best potential for enhanced precipitation to parts of the Panhandle. The deep storm tracking near the Peninsula should be accompanied by areas of strong winds over/near the North Pacific and support a period of significant precipitation from the eastern Aleutians and/or Peninsula into the southern coast and Panhandle. The latter areas should see highest totals with best flow of moisture ahead of the storm. 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 - Much above normal temperatures across portions of mainland Alaska, Sun-Wed, Nov 10-Nov 13. 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