Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 319 PM EDT Sat Apr 27 2019 Valid 12Z Wed May 01 2019 - 12Z Sun May 05 2019 Important aspects of the extended forecast for Alaska and vicinity remain very uncertain in light of continued model/ensemble spread and run-to-run variability. Not only do issues involve the position and shape of the upper high expected to be near the northern coast of the mainland as of early Wed along with flow to the southeast/south of the high, but also evolution over the Bering Sea/Aleutians and across the North Pacific. Over the past day stronger trends in the ensemble means support an operational model consensus for the upper high during the early part of the forecast period. Meanwhile there has been a noticeable adjustment in most guidance toward a farther south position of the upper high--still over the Arctic but not as far north as some prior solutions. By late in the week the 12Z GFS/00Z CMC hold the feature farther south, over the mainland (though the 12Z GFS eventually lifts a high center back to the north). Overall would prefer the cluster including the ensemble means and 00Z ECMWF/00-06Z GFS/06Z FV3 GFS which would provide more moderate adjustments from yesterday. Meanwhile recent solutions have been all over the place for timing/depth of retrograding energy to the south of the upper high. The 00Z UKMET/NAVGEM and eventually 00Z ECMWF are most aggressive with height falls reaching the mainland. Historical tendency for deepest/fastest retrogression not to work out well in such situations would recommend leaning away from those solutions. The ensemble means and nearest models provide the most reasonable approach with a weakness developing south of the upper high but to a moderate degree. Broadly speaking the new 12Z model runs appear to support this moderate approach. Farther west the guidance has gravitated toward the idea of more separated flow within an overall Bering Sea into Pacific mean trough early in the period. As a result there is increased clustering toward an area of slow-moving low pressure well south of the Aleutians. However the 12Z GFS is farther north. A separate piece of energy may produce a wave over the Bering, and some energy from the Bering/North Pacific could still end up feeding into the weakness south of the upper high. There is a signal for another North Pacific system coming into the picture to the south of the western Aleutians late in the week or next weekend. Note that ensembles show little clustering during the latter half of the period and recent cycles of the ensemble means have been inconsistent with individual low centers within a broad area of potential low pressure across the North Pacific/Aleutians. Today's forecast blend starts with a compromise between the 00Z ECMWF and 06Z GFS/FV3 GFS days 4-5 Wed into Tue and then uses increasing 06Z GEFS/00Z ECMWF mean input, reaching half means day 6 Fri and 100 percent means by day 8 Sun. This solution yields high pressure from the Arctic southeast into Canada through the period while favoring some degree of low pressure over/near the Gulf of Alaska. Also a cold front should advance southwestward across the Panhandle/eastern mainland into the Gulf before dissipating late in the period. 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