Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
635 PM EST Wed Dec 29 2021
Valid 12Z Sun Jan 02 2022 - 12Z Thu Jan 06 2022
...Overview...
The best guidance cluster maintains fairly good continuity with
the overall forecast. Early in the week consensus shows a sharp
and amplifying upper ridge over the Bering Sea through eastern
Siberia and beyond while a deep-layer low drifts southeastward
over the Northeast Pacific. There is improving agreement that the
ridge should ultimately close off an upper high that drifts
over/near or a little northeast of eastern Siberia by midweek
while energy retrogrades to some degree south of the closed high.
Surface high pressure crossing the northern mainland and settling
into eastern Canada will bring a period of cold temperatures to
the state while precipitation will tend to be confined to the
western two-thirds of the Aleutians in association with one or
more waves and then Kodiak Island/parts of the Alaska Peninsula as
easterly low level flow develops.
...Guidance Evaluation and Preferences...
Recent stronger trends for the upper ridge/high in the ensemble
means, as seen in the 12Z CMCens initially and then the 12Z ECMWF
mean after forecast preparation, have continued support for
emphasizing operational guidance to maintain reasonable strength
of the feature through the end of the forecast. Not surprisingly
the GFS/ECMWF/CMC runs are shuffling around with respect to the
upper high's center by the latter half of the period with an
intermediate solution providing a good starting point.
Model/ensemble signals have been incrementally increasing
confidence in the overall upper high scenario but what happens
with energy underneath the high (its shape, degree of
retrogression, and latitude) has much lower
confidence/predictability. Today's forecast started with a 12Z
operational model blend early and then transitioned to splitting
ECMWF/GFS input among their last two runs (12Z/00Z for the former
and 12Z/06Z for the latter) while keeping the 12Z CMC component.
This approach provided the desired average position for the
eventual upper high, shifting a bit west of yesterday's forecast
as of early day 7 Wednesday, and helped to smooth out the very
uncertain details of the developing elongated upper weakness to
the south. The blend also helped to maintain definition of the
strong high pressure crossing the northern mainland as well as the
tight gradients/strong winds over the southern mainland and
Panhandle through the forecast plus over the western half or so of
the Aleutians early in the period.
...Weather/Hazard Highlights...
Expect precipitation over the Panhandle to trend lighter on Sunday
with continued drying thereafter as Northeast Pacific low pressure
drifts southeastward and becomes gradually weaker. Much of the
mainland will see dry conditions Sunday-Thursday. The western
half or so of the Aleutians will likely see a period of
organized/enhanced precipitation and strong winds from late
weekend into the early part of next week as one or more waves
track around the western periphery of the building upper ridge.
Some locations from Kodiak Island and the Alaska Peninsula
westward may see precipitation develop as low level easterly flow
sets up but confidence in specifics is low at this time. High
pressure crossing the northern half of the state early in the week
will bring well below normal temperatures especially into southern
and eastern areas from west to east. The coldest anomalies should
start to moderate by midweek while temperatures over the northern
mainland should trend increasingly above normal. The strong
gradient between high pressure (possibly exceeding 1050mb for a
time) and the northeastern Pacific low should produce a period of
strong winds across the southern mainland and Panhandle.
Rausch
Hazards:
- Heavy snow across portions of the Alaska Panhandle and mainland
Alaska, Sat, Jan 1.
- High winds across portions of the Alaska Panhandle and mainland
Alaska, Sat-Mon, Jan 1-Jan 3.
- High winds across portions of the Aleutians, Mon, Jan 3.
- Much below normal temperatures across portions of the Alaska
Panhandle and mainland Alaska, Sun-Wed, Jan 2-Jan 5.
Additional 3-7 Day Hazard Information can be found on the WPC
medium range hazards outlook chart 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