Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
800 PM EDT Fri Aug 27 2021
Valid 12Z Wed Sep 01 2021 - 12Z Sun Sep 05 2021
...Heavy rainfall possible for portions of the southern Coast
region during the middle part of next week...
...Pattern Overview and Model Guidance...
During the extended period ridging will be in place over much of
the interior and southeast and will shift eastward as a upper
trough progresses across the Aleutians into the Gulf of Alaska. As
this happens an upper low will begin to settle in over the Bering
Sea and a series of short waves will pass through the base of the
trough, spinning up a couple of surface fronts that will track
across the Aleutian Chain and into southern coast/Alaska
peninsula. Meanwhile, to the north, a strong polar vortex and
associated mid-level westerly flow will be in place across the
Arctic and North Slope early in the week before heights begin to
rise again across the region and the Polar Vortex retreats to the
north.
In general, the latest model guidance and the ensemble means are
maintaining a decent consensus with this synoptic pattern for the
coming week. As usual, there is the typical uncertainties
regarding the timing and details of individual systems later in
the period. The 12Z GFS solution was a little fast than the 06Z
run, but both were clustered well with the 12Z ECWMF and the
ensemble means. For continuity purposes, continued to rely on a
blend of the 12/6Z GFS/ECWMF through the whole period will
increasing weighting of the ECENS, GEFS and NAEFS means through
the mid and late periods. This helped reduce spread for southern
and southeast portions of the state.
...Sensible Weather...
Light showers may occur over northern Alaska near a draped frontal
boundary early on which will keep temperatures below seasonal
average across the northern and central parts of the state. High
pressure will keep much of the interior and parts of the panhandle
drier. By Friday, much of the state could have daily temperature
near or above normal underneath of amplified upper-level ridging.
Rain will steadily spread from the peninsula to the southern as a
low pressure system lifts into the eastern Bearing Sea, as it's
attendant cold front drifts eastward through the Gulf. Rain may be
moderate to heavy at times, especially from upper portions of the
peninsula, Kodiak Island, Kenai and the Cook Inlet into Friday.
The heavier rain may reach in far southeast Alaska late Friday and
through the weekend. Along with heavy rains, these areas may also
experience gusty winds.
Campbell
Hazards:
- Heavy rain across portions of southern Alaska, Wed-Thu, Sep
1-Sep 2.
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