Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
231 PM EST Thu Feb 08 2018

Valid 12Z Mon Feb 12 2018 - 12Z Fri Feb 16 2018

...Pattern Overview, Guidance, and Predictability Assessment...

The high-latitude pattern during the period spanning February
12-16 will remain of lower confidence given a number of uncertain
details. At the start of the week, broad ridging should extend
across the northeastern Pacific with extension into far eastern
Alaska/Yukon Territory. The past few runs of the GFS have been
more aggressive with upstream height falls which erodes this mean
ridge more quickly. The guidance are at odds with another by as
early as Monday morning as the 12Z, 06Z, and 00Z GFS runs favor a
deep area of low pressure whereas the other models show the
northern extension of an anticyclone. Thereafter, the focus shifts
to the Kamchatka Peninsula where a broad mean upper low extends
laterally over the region. The core of lower heights should
feature 500-mb departures from average on the order of 2 standard
deviations. How this evolves remains uncertain as a series of
modest to perhaps potent strength impulses track eastward toward
the Bering Sea. The past few runs of the GFS have had a knack for
producing robust cyclonic circulations by mid-week, albeit with
inconsistent placements. Toward the end of the period, February
15-16, another powerful system looms back over the far
north-central Pacific. Overall, the period seems to consist of
progressive disturbances across the map which will prevent any
stagnant features from settling onto the map. However, the
uncertain details with many of these systems precludes any
significant usage of operational models. As such, except for the
00Z ECMWF which was utilized minimally through Wednesday, favored
a combination of the 00Z ECMWF, GEFS, and NAEFS ensemble means.
Dedicated more of the weighted blend toward the 00Z ECMWF ensemble
mean given better consistency as well as stronger clustered
amongst its members.
  

...Weather Highlights/Threats...

Temperatures should not change significantly during the period
with the coldest weather remaining locked over northern/eastern
sections of Alaska. Generally speaking, highs will likely settle
into the single digits to lower teens while overnight lows plunge
well below zero in many locations. Where significant thermal
inversions develop, some valley locales may see overnight readings
descend into the -20s at times. Given the active storm track
throughout the period, extensive cloud cover should spread over
the state which would limit any solar insolation for the affected
latitudes. Regarding precipitation, it is forecast to remain quite
wet throughout the period given the steady conveyor of belt of
shortwaves traversing the state. While it is difficult to hone in
on any specifics, models do depict measurable precipitation at
some point over all locations of the state. Given better moisture
transport, the wettest locations should extend along the entire
southern/southeastern Alaskan coast. The progressive nature of
such systems would limit heavier daily amounts which would suggest
this will be a longer duration event.


Rubin-Oster