Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
658 PM EST Mon Feb 12 2024
Valid 12Z Fri Feb 16 2024 - 12Z Tue Feb 20 2024
...Overview...
The large-scale upper pattern over Alaska late this week will
consist of an amplified ridge extending over the Yukon/Southeast
Alaska, gradually relaxing into early next week. The initial ridgy
pattern should produce well above average temperatures across most
of the state, especially during this week with gradual moderation
into next week. Mean troughing will be in place farther west from
the western Bering Sea to the Aleutians into the northern Pacific.
Expect heights to lower further atop the Aleutians by the weekend
as an upper low comes overhead and supports a Bering Sea surface
low/frontal system.
...Guidance Evaluation and Preferences...
Model guidance remains persistent in showing mid-upper ridging
expanding west across much of the state this week. Models vary
more regarding the weakening of the ridge with time. In
coordination with the Alaska WFOs, the preference is to maintain
some ridging into next week, given typical model biases to break
down ridging more quickly than it usually occurs. Thus leaned away
from the 12Z CMC solution that dove energy/troughing from the
Arctic southwest across the state early next week. The ensemble
means were reasonably agreeable
Another main area of uncertainty is with an upper low and its
surface reflection coming eastward atop the Aleutians and
potentially slowing. The CMC remains an outlier with this feature
as well, as it does not close off the upper low as much but has
more of a phased trough solution, not allowing the surface low to
go as far east as other guidance. Meanwhile the UKMET through its
period seemed to be fast/southeast with the upper and surface
lows. The ECMWF and GFS appeared to be a better middle ground for
the low track that matched the ensemble means better at least
through Sunday. After that spread increases for the low tracks,
including the uncertain potential in the GFS runs for a shortwave
and surface low coming through the northern Pacific toward the
Alaska Peninsula. GFS runs also may be breaking down the ridge in
the northeast Pacific faster than preferred.
The WPC forecast incorporated some GEFS and EC ensemble means even
for the early part of the forecast given the deterministic model
spread. The rest of the model blend was composed of the 06Z/12Z
GFS and the 12Z ECMWF considering the issues with the CMC/UKMET.
Gradually increased the weighting of the ensemble means to over
half by Days 6-8 as spread increased.
...Weather/Hazards Highlights...
The most persistent precipitation chances during the period should
focus across the Alaska Peninsula into the favored terrain north
of Bristol Bay, as well as Kodiak Island and the southern Kenai
Peninsula. Mean southeasterly flow (easterly and convergent at the
surface) with Pacific moisture will support this precipitation.
Precipitation types may be varied in some areas, but mostly rain
and snow are expected as opposed to freezing rain. Multi-day
precipitation totals could be several inches in terms of liquid
equivalent in localized areas favored by upslope flow in this
pattern, but heavy totals should not be widespread. Into late this
week, some precipitation looks to stretch north across the western
mainland, but chances for precipitation there will gradually
lessen by the weekend as the upper ridge expands over that region.
Meanwhile the eastern half of the Mainland and into Southeast
Alaska should start out quite dry underneath the upper ridge, but
relaxation of the ridge may allow for some moist inflow and
increasing precipitation chances by the weekend into early next
week. Timing and amounts are uncertain dependent on how strongly
the ridge holds on. Gusty winds are possible at times from the
Alaska Peninsula into southern Alaska, especially Thursday-Friday.
Additionally, we are monitoring the potential for strong winds for
the Aleutians by early next week dependent on the exact surface
low track.
The ridgy pattern will also favor above normal temperatures across
a majority of the state. The greatest anomalies should set up in
western to northern parts of the mainland and could be more than
30 degrees milder than normal. Above freezing temperatures are
possible well into the southwestern mainland especially through
Friday. Gradual cooling is likely by next weekend but temperatures
should still be above average in most places, perhaps reaching
around normal for eastern parts of Interior Alaska by
Monday-Tuesday. Near normal temperatures are forecast for the
Panhandle.
Tate
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