Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
558 PM EST Sat Jan 23 2021
Valid 12Z Wed Jan 27 2021 - 12Z Sun Jan 31 2021
...Major Bering Sea Storm to Threaten Alaska and the Gulf of
Alaska mid-later next week...
...Overview and Guidance/Uncertainty Assessment...
Quite an active storm track on tap with a powerhouse closed
low/trough and ~950 mb surface low slated to reach the Aleutians
and Bering Sea into Wednesday that will slowly fill while spinning
over the Bering toward western Alaska Thursday into Friday. This
system already has a well defined mid-latitude satellite signature
off eastern Asia and offers a substantial maritime threat. Ample
downstream energy transfers over the AKPen/Southwest AK/Kodiak
Island and into the Gulf of Alaska offer subsequent well organized
maritime low re-development. Guidance flow evolutions have trended
in much better agreement, bolstering forecast confidence quite a
bit.
Accordingly, the WPC Alaskan medium range product suite was
derived from a well clustered blend of the 12 UTC
GFS/ECMWF/Canadian models days 4-6 (Wednesday-Friday) along with
the 19 UTC National Blend of Models. Added the GEFS/ECMWF ensemble
means to the composite blend days 7-8 for max WPC product
continuity through next weekend in an amplified pattern with above
normal predictability.
...Weather/Hazards Highlights...
The deep Bering Sea storm will spread heavy wrapping precipitation
and a threat of high winds/waves to the Bering Sea and into the
Aleutians midweek, and an enhanced snow risk into
western/southwest Alaska Thursday into Friday with approach.
Amplified upper ridging building over the Interior/North Slope in
advance of the deep low will meanwhile weaken, slated to reform
back over the Bering Sea next weekend. Forecast spread increases
in Arctic stream flow rounding the ridge, but the WPC guidance
blend allows a decent venue for impulse energy to dig into a
cooling/unsettled Interior in increasing amplitude flow.
Underneath, downstream transition across the AKPen/Kodiac Island
will result in a pattern favorable for deepened northern to
eastern Gulf of Alaskan low developments later week into next
weekend, but recent guidance trends do show a slightly more
offshore track from the Southeast Panhandle. WPC PoPs guidance and
associated parameters have decreased accordingly from yesterday as
per coordination with WFO Juneau. However, the well organized low
should remain a maritime threat into next weekend.
Schichtel
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards 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