Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 306 PM EST Wed Nov 06 2019 Valid 12Z Sun Nov 10 2019 - 12Z Thu Nov 14 2019 Overall there is still considerable uncertainty over important forecast details even though there are some common themes in the guidance regarding large scale flow. There is some agreement that a weakness will develop within the initial mean ridge that extends from the British Columbia coast through the mainland--with some energy possibly crossing the northeastern Pacific/Gulf of Alaska and cyclonic flow developing to the southwest of an Arctic/Canadian Archipelago upper low, while an upper high closes off northwest of the mainland. Path and strength of northeastern Pacific/Gulf energy will be key for associated surface low pressure, with guidance showing a broad envelope for low tracks between Kodiak Island and the Alaska Panhandle. This part of the forecast is very difficult as recent ECMWF/CMC/UKMET runs are fairly aggressive to bring energy into the downstream ridge leading to low tracks toward the Panhandle, while the ensemble means are much more subdued with the energy (seemingly more plausible given occasional tendencies for guidance to break down ridges too quickly) with a farther west low track. Latest GFS runs are more compatible with the GEFS/ECMWF mean surface low but even the GEFS mean suggests the GFS could become to slow with the energy aloft. A compromise may ultimately be the best option. At higher latitudes there are persistent differences with the southwestward amplitude of cyclonic flow with an intermediate solution appearing best. Fortunately surface solutions are fairly similar with a cold front pushing into the mainland from the north while high pressure becomes established over the Arctic. Farther west there is plenty of spread as well. Early in the period ECMWF/CMC runs have been closing off a concentrated system over the southern Bering Sea along an initial wavy front while most other guidance is downplaying such a feature. Then there is a decent signal for a significant North Pacific into southern Bering Sea storm which could have some input from Super Typhoon Halong, possibly combined with a mid-latitude Pacific wave that catches up from the west. GFS runs have generally been more consistent for track longitude than the ECMWF over recent days (western half of the spread versus every 1-2 runs switching between eastern and western tracks). A westward adjustment in the ECMWF mean compared to yesterday now brings it into agreement with the GEFS mean so there is a little more confidence for leaning away from the eastern part of the envelope. The 00Z/12Z GFS runs track the storm farther north than consensus though, and other guidance even keeps the system south of the Aleutians for most of its existence. The means provide a reasonable intermediate path. Finally, toward the end of the period the ensemble means have been fairly stable in advertising another system entering the domain from the west, possibly brushing the Aleutians by day 8 Thu. With fairly low confidence given the spread in the guidance, the forecast blend emphasized the 06Z GEFS/00Z ECMWF means with some GFS input where similarities existed--06Z-12Z runs early and only the 06Z run late. The manual forecast adjusted this blend a little stronger for mass fields and corresponding winds. While day-to-day details are uncertain the overall pattern should favor highest precipitation totals along the southern coast and Panhandle with meaningful totals extending farther west as well. The potentially deep northern Pacific/Aleutians storm may produce areas of strong winds. 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 northern Alaska, Sun-Tue, Nov 10-Nov 12. 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