Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
752 PM EDT Wed Oct 26 2022
Valid 12Z Sun Oct 30 2022 - 12Z Thu Nov 03 2022
...High winds across the Alaska Peninsula/Kodiak Island and heavy
precipitation over the Panhandle will continue early next week
with a strong low...
...Overview...
As the period begins Sunday, an upper low and a strong surface low
will be located across the eastern Gulf of Alaska. High winds are
a threat across the Alaska Peninsula into the southwestern
mainland and Kodiak Island on the backside of the low, while heavy
precipitation is likely across the Panhandle along with the
possibility of some gusty winds. Through the first half of the
workweek, upper ridging should move across the state, temporarily
quieting the overall weather, while an upper low moves eastward
across the Bering Sea. This feature and potential troughing
farther south into the Pacific is likely to spread some
precipitation first to the Aleutians and then into western and
southern parts of the state as the trough shifts into the Mainland
Wednesday-Thursday.
...Guidance/Predictability Assessment and Preferences...
Model guidance remains in generally good agreement with potent
energy producing an upper low and strong surface low centered over
the eastern Gulf of Alaska Sunday, with only minor differences in
the placement and strength. This low is likely to remain in a
favored region just west of the northern Panhandle through early
next week while weakening. Farther upstream, a closed upper low is
becoming more likely over the Bering Sea around Mon-Tue with
better model agreement compared to a day ago, along with a surface
low there. But farther south across the Aleutians and Pacific,
while there is general agreement for troughing, differences in
shortwaves and in surface lows abound. CMC and EC runs have been
farther southeast compared to the GFS runs that show a surface low
near the Aleutians moving toward the southwestern mainland Tue,
which could be quite impactful if it were to occur. Ensemble means
may be combining the southern and northern low features as they
generally indicate one low to the north of the Aleutians, so this
did not provide a reason to lean one way or another. Despite these
differences, at least the models/means are in fairly good
agreement that upper troughing will trek eastward gradually and
reach the Mainland around Wed-Thu.
The WPC forecast was based on a blend of the GFS/ECMWF/CMC
deterministic models early in the forecast period given the
reasonable agreement. Then as model spread with the details
increased, the forecast incorporated the GEFS and EC ensemble
means and gradually increased their weighting to about half by day
8.
...Weather/Hazards Highlights...
The Gulf of Alaska weekend low will be the main player causing
significant weather at the beginning of the medium range period.
The tight pressure gradient with the low will cause concerns for
strong winds stretching across eastern portions of the Aleutians
into the Alaska Peninsula as well as Kodiak Island beginning in
the short range period; then even as the low pulls away,
northwesterly flow could cause gap wind issues in some of the same
areas through around Monday. The low should tap into a long fetch
of Pacific moisture to cause heavy precipitation across the
Panhandle lingering into Sunday. Locations seeing significant
totals from a short range event may be sensitive to the additional
activity during the weekend. Some gusty winds are possible for the
Panhandle as well but may be less hazardous than farther west.
After that, there are likely to be some wet and possibly windy
periods across the Aleutians for the first half of next week with
troughing overhead, but there is still considerable uncertainty
with the details at this time. But the general trend should be for
precipitation to shift eastward mainly across southern Alaska
through midweek and beyond as the trough moves east.
Below normal high temperatures should persist over a majority of
the state including the Panhandle through the period, with the
greatest anomalies over southern areas. Locations near the
northern coast of the mainland may remain somewhat above normal.
Low temperature anomalies may overall be more moderate, but still
below average over most areas except for the North Slope. The
Panhandle may see a mix of above/below average lows depending on
location and day.
Tate
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle,
Sat-Sun, Oct 29-Oct 30.
- High winds across portions of mainland Alaska, Sat-Mon, Oct
29-Oct 31.
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