Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 PM EST Sat Feb 10 2018

Valid 12Z Wed Feb 14 2018 - 12Z Sun Feb 18 2018

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

While the general synoptic-scale pattern is agreed upon, the short
wavelength between individual features makes for a rather nebulous
forecast. A mean negative height anomaly should literally remain
fixed over the north-central Pacific extending up toward the
Kamchatka Peninsula. Several waves of energy should churn eastward
toward the Bering Sea and Aleutians, each of which have the
potential for spinning up a modest to potentially stronger wave of
low pressure. By next weekend, a more consolidated axis of height
falls pushing toward the far western Aleutians will drive a strong
positive height anomaly over western Alaska. There are some
suggestions 500-mb height anomalies underneath this ridge could
exceed 2 standard deviations. While the guidance vary in the
details, there is actually greater confidence deeper into the
forecast as the pattern takes on a much longer wavelength.

During the Wednesday through Friday timeframe, operational models
continue to advertise the mentioned wave train of shortwaves
tracking toward the Bering Sea. Run-to-run model continuity is
poor to say the least as the 12Z GFS placed a 959-mb cyclone
center over the southern Bering Sea while the preceding run
depicted a pair of weak low centers to either side. Such
comparisons of other operational solutions prove to have similar
issues which forces a full ensemble-based approach here. Decided
to roll with an equal blend of the 00Z GEFS/ECMWF ensemble means
throughout the entire forecast. The 00Z NAEFS ensemble mean was
decidedly weaker with the upstream axis of low pressure so favored
other ensemble solutions rather. The blend utilized may be a tad
slow to build next weekend's ridge as the 00Z ECMWF ensemble mean
has been trending flatter.


...Weather Highlights/Threats...

The coldest conditions during the period can be expected across
northern/eastern Alaska with daily high temperatures struggling to
get above 0 degrees in many locations. Overnight, readings will
likely plunge into the negative teens in some of the favored
locations where low-level thermal inversions set up. Meanwhile,
the usual warm spot should be across the Aleutians with highs
generally in the upper 30s to lower 40s given persistent maritime
influences. Given the conveyor belt of shortwaves lurking
upstream, widespread cloud cover will be the norm over the state
although building heights next weekend should clear out the skies
a bit. Precipitation threats are forecast to be numerous although
the transient nature of each system should lead to a series of
breaks. Except for the southern/southeastern coasts of Alaska
where surface temperatures will likely afford mixed precipitation
types, snowfall should dominate over more interior locations. In
addition to the cloudy, unsettled conditions, winds should pick up
across the Aleutians by next Saturday in advance of a strong cold
front.


Rubin-Oster