Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
732 PM EDT Tue Oct 29 2024
Valid 12Z Sat Nov 02 2024 - 12Z Wed Nov 06 2024
...Stormy pattern late this week into next with potential for
multiple episodes of significant precipitation/wind for southern
Alaska...
...Overview...
Models continue to indicate a relatively broad and weak elongated
upper low across the Bering Sea into the weekend. Shortwaves
rounding the elongated low will provide support for at least one
impactful surface low, reaching somewhere near the Alaska
Peninsula as the period begins Saturday, with a threat for high
winds and enhanced precipitation. After that, a surface low may
approach Haida Gwaii or so early next week, but a better and more
coherent signal exists for a North Pacific surface low to
strengthen notably south of the Aleutians by around Monday as the
Bering upper low combines with energy stemming from current
Typhoon Kong-rey and possibly Arctic energy quickly dropping
south. The deepening upper troughing over the Bering Sea southward
into the Aleutians and northern Pacific should promote ridging
developing across the Mainland to Panhandle after a mildly troughy
pattern over the weekend. The northern Pacific upper low looks to
move northeast and cross the Aleutians or Alaska Peninsula and
reach Bristol Bay or so by next Wednesday.
...Guidance Evaluation/Preferences...
Model guidance continues to have notable spread for the early part
of the period this weekend with a surface low located somewhere
from Bristol Bay to the Alaska Peninsula to Kodiak Island to the
western Gulf of Alaska. The CMC/UKMET maintain a farther west
Bristol Bay position, with the 12Z ECMWF a little farther south
over the AKPen. GFS runs on the other hand are farther east in the
Gulf, but so are most of the EC-based AI/ML model runs. Ensemble
members show support for both low positions and the ensemble means
are in between. The 00Z ECMWF had the best middle ground position
like the ensemble means near Kodiak Island, so preferred a model
blend heavy on those as an intermediate solution at this time.
This was not too far off from continuity but a little faster/east.
The exact low placement will determine impacts such as wind speed
and direction.
Behind that system, models vary on the position and timing of a
shortwave moving through the northeast Pacific with a surface low
accompanying it around Monday, but at least there is better
agreement today in this feature existing. GFS runs are slower than
the non-NCEP models to bring this low into Haida Gwaii or so, but
meanwhile ensemble means are indicating low pressure farther north
in the Gulf compared to more southern deterministic models. So
still considerable uncertainty with this feature.
Then upstream, at least a piece of vorticity coming from what is
currently Typhoon Kong-rey is forecast to turn northeast and
restrengthen as an extratropical low in the northern Pacific.
Models become quite strong with this low, in the 940s or below,
but at varying times. The ECMWF runs deepen the low particularly
late but are also fast/east with it compared to the CMC and GFS.
The latter models cluster better with the ensemble means. Most
AI/ML models were slower than the EC as well, but a complicating
factor is that the newer 12Z AIFS shows the low even farther east,
increasing uncertainty.
The WPC forecast favored the 00Z EC and the EC/GEFS ensemble means
early in the period with lesser components of other models.
Gradually transitioned away from both ECMWF runs and increased the
ensemble means to near half by Day 6 and to 70 percent by Days 7-8
given the spread.
...Weather/Hazards Highlights...
An active weather pattern is forecast across southern Alaska with
periods of enhanced precipitation and winds. One such system, the
low near Kodiak Island or nearby, will increase precipitation
chances from the Alaska Peninsula into Southcentral into Saturday
and toward Southeast over the weekend. Widespread precipitation
amounts are likely to stay below criteria for the Hazards Outlook,
but locally heavy amounts are possible. However, high winds could
warrant a Hazard area on the map for the eastern Aleutians and
western Alaska Peninsula Friday into Saturday where models are
more agreeable in showing an area. The next potential surface low
near Haida Gwaii may lead to locally heavy precipitation in the
southern Panhandle early next week. Then the deep surface low
moving from the northern Pacific northeastward could cause another
round of high winds for the Aleutians/Alaska Peninsula by next
Tuesday. Strong winds may move into the Southwest Mainland
depending on the eventual low track. Precipitation amounts will
also increase once again from the Aleutians to Alaska
Peninsula/southwest Mainland to Southcentral on Tuesday and toward
Southeast by next Wednesday. Meanwhile, rounds of snow showers are
possible farther north through the period.
Most locations will see above average temperatures this weekend
and gradually warming into next week, with the possible exceptions
of the Seward Peninsula, parts of the higher mountain peaks, and
the Panhandle remaining cooler. In most cases the anomalies for
morning lows should be greater than anomalies for daytime highs.
High temperatures will generally be in the upper teens to 20s in
the Interior and North Slope, with 30s and low to mid 40s in
southern areas.
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