Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
718 PM EDT Tue Apr 23 2024

Valid 12Z Sat Apr 27 2024 - 12Z Wed May 01 2024

...Overview...

During this period an upper/surface low will drift east from the
the Aleutians/Alaska Peninsula on Friday, across the Northeast
Pacific ocean over the weekend into early next week before pushing
into Southeast Alaska and British Columbia. North and east of this
feature, upper ridging will stretch from Southeast Alaska
northwest into the northern part of the state late week but erode
with time. Another large trough upstream with one or two rounds of
passing energy will track through the Bering Sea with a course
toward the western Alaska coast; however there is a lot of
uncertainty with the details of this feature.

...Guidance Evaluation and Preferences...

Initially, the latest model runs have decent clustering with the
upper low and upper ridge features particularly with the low
undercutting the ridge over portions of eastern to northern
Alaska.
The trend for a steadier progression of the low eastward persists,
therefore maintained continuity by utilizing a blend of the
deterministic guidance favoring the 12Z ECMWF and GFS. Like
previous runs, the model spread increases yielding low confidence
for the forecast next week. By Sunday there is some uncertainty
with how much energy may remain/come in near Bristol Bay. This
makes the ECMWF (which has a ridge) out of phase with the CMC that
lingers a small upper low there and the GFS runs that push
additional energy in. Then a larger scale trough may push into the
Bering and the Aleutians and western Alaska, but the timing is
quite variable. Once again, the GFS solutions depict a faster
progression bringing the trough east than the ECMWF and CMC and
leads to more out of phase issues. The inclusion and weighting of
the EC and GEFS ensemble means were quickly increased through the
middle and latter periods, totaling to 60% percent by Wednesday.
The means are pretty zonal due to the differences across the
ensemble members but hopefully models will converge with time.


...Weather/Hazards Highlights...

Gusty winds and precipitation will accompany the upper and surface
lows late this week for portions of the Aleutians to Alaska
Peninsula, into the southwest Mainland toward Kodiak Island and
the Kenai Peninsula, with moderate amounts Friday lowering on
Saturday. At this time the wind speeds will likely remain below
the hazardous threshold. Some precipitation is likely over the
weekend for Southeast Alaska as moist inflow increases ahead of
the low moving east. Generally light amounts are forecast in
northern parts of the Panhandle with more moderate amounts in
southern parts. As another system approaches the Bering, Aleutians
and western Alaska, precipitation chances will renew. The timing
and location of this feature will determine where the heavier
amounts will setup for the Aleutians, southwestern and
south-central Alaska. Meanwhile the northern half of the Mainland
can expect generally dry conditions.

A majority of the state will have above normal temperatures
through the end of the month with the highest anomalies likely
positioned over the Interior. To the north of a front settling
over the north-central mainland, cold high pressure over the
Arctic may keep temperatures near to somewhat below normal,
especially across the North Slope. Locations near the Southcentral
coast and northern Panhandle may also see near or slightly below
normal readings.


Campbell/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