Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 346 PM EDT Tue Apr 16 2019 Valid 12Z Sat Apr 20 2019 - 12Z Wed Apr 24 2019 The primary focus of the extended forecast will be a likely translation of upper troughing/embedded low center(s) from the western mainland and extreme eastern Bering Sea into or near the Gulf of Alaska in the form of an upper low. Latest GEFS/ECMWF/CMC ensemble means agree fairly well with this evolution along with arrival and subsequent persistence of surface low pressure over the Gulf of Alaska region. Not surprisingly operational models and some individual ensemble members differ significantly with specifics. Within this evolution expect highest precipitation totals to extend from the Panhandle to the Kenai Peninsula. Depending on how details at the surface and aloft work out, meaningful amounts may extend farther west to Kodiak Island and the Alaska Peninsula. During the weekend (days 4-5) the most notable differences involve the track of leading low pressure. The 00Z ECMWF is in the southeastern/eastern 10-25 percent of the full ensemble envelope with a track reaching close to the southern Panhandle. Previous ECMWF runs aligned better with other models and the ensemble means (including the 00Z ECMWF mean), so initial preference was to use more of the 12Z/15 run as part of a multi-model consensus early in the period. Newly arriving 12Z guidance is significantly reducing confidence in any specific solution. The 12Z GFS adjusted to the 00Z ECMWF scenario--which is now further extended by the new 12Z ECMWF. On the other hand the 12Z UKMET/CMC/GEFS mean remain with the farther westward majority cluster. During this time frame subtle differences within and between progressive mid-latitude Pacific flow and features within/around the western mainland trough aloft will have a significant impact on the ultimate track of low pressure. Thus it may take into the short range period before guidance resolves this aspect of the forecast. Farther west there is better clustering for a wave and trailing cold front dropping southeastward over the Bering Sea. For Mon-Wed the ensemble means have been fairly stable in advertising an upper low settling over the Gulf of Alaska but the past couple 6-hourly GEFS runs (along with recent GFS runs) have been holding the feature a little farther west than the 00Z GEFS/ECMWF/CMC means and 00Z CMC. Surface low uncertainties continue beyond those seen for days 4-5. Among solutions that bring the initial wave into the Gulf, some bring it at least as far north as the southern coast while others keep it offshore. The wave that drops through the Bering during the weekend may ultimately wrap into the Gulf or even westward--though most ensembles say not to the extent of the 12Z GFS--or else remain well southward and possibly dissipate/merge with surrounding flow. There is also potential for separate mid-latitude waviness to track into the Gulf (or alternatively remain well suppressed). All of these uncertainties provide strong support for trending the forecast increasingly toward the 00Z ensemble means mid-late period. Among operational runs the 00Z CMC could be retained the longest due to better agreement with the means. The resulting solution maintains reasonable continuity with one dominant surface low meandering east-southeast of Kodiak Island. Rausch Bullet points from the WPC Days 3-7 Hazards chart can be found at: https://www.wpc.ncep.noaa.gov/threats/threats.php - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Sun-Mon, Apr 21-Apr 22. 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