Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
747 PM EDT Mon May 27 2024
Valid 12Z Fri May 31 2024 - 12Z Tue Jun 04 2024
...Overview...
A first upper trough will pivot across the northeast Pacific late
week, while another upper low tracks from atop the western
Aleutians Friday to cross the eastern Aleutians over the weekend
and set up in the northeast Pacific early next week. This pattern
will support precipitation spreading into the Southern Coast of
Alaska with cooler than normal temperatures. Upper ridging to the
northeast of this storm track should promote mild to warm
temperatures over the Interior with some lighter convective
showers, at least into the weekend, but with more uncertainty
early next week as Arctic energy may approach.
...Guidance Evaluation and Preferences...
Model guidance is fortunately rather agreeable with the larger
scale systems, at least through the weekend. An upper trough and
an associated surface low will be located south of Kodiak Island
as the period begins Friday and pivot toward the Gulf into
Saturday, with just some minor spread in the models. Upstream,
another upper/surface low is forecast to track east across the
Aleutians Friday-Saturday, likely crossing the eastern Aleutians
into the northern Pacific by Sunday. Some model spread is in place
with the timing and placement of systems, but certainly within
reason for the medium range, with no notable outliers. Additional
energy rounding the base of the upper low should help to
consolidate it and possibly deepen the surface low in the
northeastern Pacific early next week.
To the north and east of the storm track, a generally ridgy
pattern aloft should be in place across much of the Mainland into
late week. Model guidance does show some possibility of Arctic
energy diving southwest toward or into the northwestern Mainland
by the weekend or early next week. The ECMWF and CMC have the
energy in the form of a closed upper low staying west of Alaska,
while the GFS runs take the low across the northwest Mainland
toward the Bering Strait but with varied timing. Interestingly the
ECMWF-based AIFS (machine learning model) looks more like the GFS
in its track. Overall this is an uncertain aspect of the forecast
with low confidence.
Given these considerations, the WPC forecast used a blend of the
deterministic guidance early in the period. As typical, increased
the proportion of ensemble means as the period progressed,
reaching around half the blend by Days 7-8 given the increasing
uncertainty especially in northern areas.
...Weather/Hazards Highlights...
No significant weather hazards are forecast through the period
with rain amounts generally remaining modest overall. The Southern
Coast of the state--across the Alaska Peninsula (and Kodiak
Island) to the Kenai Peninsula and Prince William Sound to the
Panhandle--can expect some precipitation chances given the
favorable troughing and expected low tracks. Some localized
heavier totals in typically favored areas of terrain are possible,
but heavy amounts should not be widespread. Farther north into the
Interior to Brooks Range, some convective showers yielding light
to modest amounts are possible as well, with most shower coverage
in the afternoons/evenings. Depending on the eventual flow pattern
over the Mainland next week, precipitation may become more
widespread and heavier, but this remains uncertain. River flooding
is a possibility in a spot or two with the seasonal ice breakup;
see the Alaska-Pacific River Forecast Center for details.
Interior Alaska is likely to see the mildest temperatures across
the state, with highs in the 60s to low 70s late this week into
early next week, around 5-10 degrees above average. The North
Slope is likely to be closer to or below average, with highs just
above the freezing mark in the Arctic Coast communities. For the
southern coast, temperatures at least for highs are forecast to
stay below normal given the troughing and active pattern in place,
with 40s and 50s for the most part. However, 60s look to sneak
into Anchorage to Talkeetna.
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