Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 303 PM EST Mon Feb 12 2018 Valid 12Z Fri Feb 16 2018 - 12Z Tue Feb 20 2018 ...Pattern Overview, Guidance, and Predictability Assessment... An ever persistent axis of lower heights extending back over the north-central Pacific up toward the Kamchatka Peninsula will continue to spit out a series a shortwaves taking aim at the Bering Sea. All the while, a progressive low-amplitude pattern across the Gulf of Alaska will bring a wave of low pressure toward the Alaskan panhandle early Friday. Over the weekend, a rather marked pattern change unfolds as significant mid-level height rises build over the state. It is a rather unanimous signal in the operational and ensemble guidance with 500-mb height anomalies likely reaching the 1.5 to 2 standard deviation range. Toward the end of the weekend, some of the operational solutions try to erode portions of this positive height anomaly before rebounding by the early part of next week. Overall, while synoptic-scale agreement exists across the map domain, it will be difficult to pinpoint with any precision the multiple waves traversing the region. Given the building downstream ridge, a track up toward the northern Bering Sea is likely with many of these waves. Each embedded shortwave should shear in the process leading to a marked increase in surface pressures as the feature gains latitude. By next Monday, February 19, a rather impressive cyclone moves west of the Aleutians with pressures in the 960-970 mb range. Due to placement uncertainties, an ensemble based approach favors much higher pressures which validates the amount of spatial spread present. Regarding the forecast itself, was able to utilize a combination of the 06Z/00Z GFS and 00Z ECMWF in conjunction with their ensemble means through Saturday before moving toward an equal blend of the 06Z GEFS/00Z ECMWF ensemble means. ...Weather Highlights/Threats... The beginning of the period should be quite chilly, particularly over sections of north-central Alaska. While high temperatures will reside in the negative single digits, overnight readings could plunge well into the -20s as an arctic high sits over eastern Alaska this weekend. Prime locations for such chilly temperatures will be within valleys where strong low-level thermal inversions should be tough to mix out. A gradual warming trend is anticipated thereafter as the surface high moves southeastward allowing for return flow in advance of the next system. Initially, it will be rather wet over southeastern Alaska but will turn more showery as the mid-level shortwaves traverse the region. Except for northwestern Alaska, generally north of an advancing warm front, the state should become rather dry before the next powerful system approaches. From west to east, conditions will likely become wet over the Aleutians this weekend with 12-hour amounts generally maximizing in the 1 to 1.50 inch range. The parent boundary should weaken while moving downstream as it encounters the stout ridge with additional precipitation chances looming back over the western Aleutians with the next system. Depending on the strength of the waves pushing through the Bering Sea, there could be some gusty southerly winds ahead of some of these cold fronts across the Aleutians. Rubin-Oster