Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 340 PM EDT Sun Apr 28 2019 Valid 12Z Thu May 02 2019 - 12Z Mon May 06 2019 There are still multiple uncertainties in the forecast but compared to previous days there is improved clustering among models/means for some features. One such improvement is for the upper high expected to drift over the Arctic during the period. Not surprisingly the operational models have been more variable/diverse than the means but even the means have waffled on the latitude of the feature. The current model/mean cluster is close to and with time perhaps just a bit north/west of the multi-day average of the means. The other system whose clustering looks much better is potentially strong low pressure whose track spread currently centers along the Aleutians but includes the North Pacific and Bering Sea. Latest guidance is faster with this storm versus solutions that had at least a hint of it yesterday. Meanwhile confidence remains quite low for details within a mainland upper weakness which may incorporate some flow from northwestern Canada. There are still many different ideas on depth/timing of retrograding shortwave energy. Prefer to hold onto a moderate solution given the tendency for deepest/fastest retrograding solutions south of a closed high not to work out the best. Trends over the past few days do seem to be hedging away from prior solutions that had been on the deeper side of the spread with retrograding energy. Another low-confidence aspect of the forecast will be upper dynamics/surface low pressure over and southwest of the southwestern mainland early in the period. Predictability is low due to the relatively small scale of energy aloft. Some of this flow may also feed into the aforementioned weakness to the south of the Arctic upper high. New 12Z guidance has changed enough with the combination of these uncertain upper features that the front initially near the Panhandle/southeastern mainland does not progress southwest into the Gulf as seen in prior established consensus (and today's manual forecast). This change will have to be watched for confirmation in future runs. The preferred forecast blend started with a 70/30 model/mean weight for days 4-6 Thu-Sat, incorporating the 00Z ECMWF and 00-06Z GFS (more 00Z run due to its less aggressive retrograding height falls over the mainland) along with the 06Z GEFS/00Z ECMWF means. Relative agreement in the larger scale evolution held up well enough to allow for nearly even model/mean input by day 8 Mon. 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