Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
635 PM EDT Fri Jun 25 2021
Valid 12Z Tue Jun 29 2021 - 12Z Sat Jul 03 2021
...Unsettled weather expected from portions of the Aleutians to
the Southern Coast...
...Overview and Guidance/Predictability Evaluation...
The latest models and ensembles continue to advertise that an
upper low will drift slowly eastward to the south of the Aleutians
before possibly shifting northward into the Bering Sea,
potentially blocked by upper level ridging building over the
Mainland late next week. Perturbations rounding the base of the
trough will send a couple of waves of low pressure/systems into
the Aleutians through the week, enhancing potential for wet and
windy weather. Troughing may also briefly move through northern
parts of Alaska before the strong ridging drives it eastward.
Models and ensembles generally agree on this overall pattern,
although continue to exhibit plenty of uncertainty regarding the
details. There are some timing and strength differences with how
quickly ridging builds into central and eastern Alaska, which
would affect steering flow for the Aleutians low. By day 7-8,
weaker ridging in the 12z ECMWF would want to pull the low farther
east into the AK Peninsula, although the GFS (and the ensemble
means) are more consistent with showing strong ridging which
blocks eastward movement and pushes it north into the Bering Sea.
As such, WPC trended towards a majority ensemble mean blend the
latter half of the period, with some modest contributions from the
12z GFS for added system definition and details. The first half of
the period leaned very heavily on the 12z operational ECMWF and
GFS. This approach fits well with yesterdays continuity as well.
...Weather/Threats Highlights...
Surface lows and fronts ejecting into the Aleutians towards mid
next week is expected to set up a wet and windy pattern from
especially the eastern Aleutians into the Alaska Peninsula and
Kodiak Island/Lower Cook Inlet. This should bring moderate to
locally heavy rainfall to the region, although exact amounts
remain uncertain. Gusty winds and high waves may also accompany
these systems as they cross the region. To the north, a cold front
dropping through Northern Alaska may bring some modest
precipitation to parts of the North Slope region and Brooks Range,
with snow possible in the higher elevations. In terms of
temperatures, upper troughing across the state early in the week
will keep temperatures cool, especially across the Brooks Range
and northern Slope region where daytime highs as much as 20
degrees below normal are possible. As upper level ridging builds
over the state during the later half of next week, temperatures
should warm to above normal, with pleasant highs in the 70s for
parts of eastern Alaska. Southern Alaska and back to the Aleutians
should remain near or below normal underneath cloudy skies and
unsettled conditions.
Santorelli
Additional 3-7 Day Hazard Information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
Hazards:
- Heavy rain across portions of mainland Alaska and the Aleutians,
Wed-Fri, Jun 30-Jul 2.
- High winds across portions of mainland Alaska and the Aleutians,
Wed-Thu, Jun 30-Jul 1.
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