Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
544 PM EDT Wed May 05 2021
Valid 12Z Sun May 09 2021 - 12Z Thu May 13 2021
...Overview and Guidance Evaluation...
Most guidance continues to show a deep-layer mean low over the
Aleutians/southern Bering Sea that persists through the weekend
before weakening early next week. Shortwaves ejecting from the
mean low should produce a series of wavy frontal systems that
cross the Aleutians through the Alaska Peninsula and Gulf of
Alaska. Although the consensus clusters a little better than
average, individual solutions suggest numerous uncertainties with
the forecast that would keep confidence in any one solution low,
given continuing run to run changes.
On Sunday, the next of the series of waves forms east of the
parent low and moves from the Aleutians to the open waters
southeast of Kodiak Island. On Monday, this low north towards the
Gulf of Ak, where the low stalls and decays on Tue 11 May.
On Monday, the next forming ave of low pressure moves south of the
Aleutians, with better than normal clustering, without unanimity.
On Tue and Wed, the system moves slowly northeast, possibly
reaching the AK peninsula or even into the adjacent southeast
Bering Sea before decaying and merging with the upper low.
By mid week, the next 500 mb low moves from south of Kamchatka
east near 50N, spawning cyclogenesis, with the low approaching the
lower Aleutians and possible arriving by the middle of next week.
There is better than typical agreement the low will develop, with
timing differences on Wed and Thu 13 May, as the GFS and Canadian
global are about half a day faster than the 00-12z ECMWF and it
ensemble mean. The agreement lead to a blend of the last 2 ECMWF
runs and ECMWF Ensemble Mean to mitigate the differences among
solutions, as usually with closed lows the slower solutions are
more correct.
...Sensible Weather...
Expect the highest probability of precipitation and moderate
totals to extend from along the Alaska Peninsula to the Kenai
Peninsula, with another max in southeast Alaska/panhandle in
tandem with each wave of low pressure/associated fronts. Scattered
diurnal convection is possible inland as a quasi-stationary front
lingers over interior AK. The Aleutians will likely see unsettled
conditions with periods of rain with each low later this week and
again in the middle of next week.
With above normal heights across interior and northern AK,
temperatures are favored to be above normal in most areas.
Persistence of the arctic high to the north should maintain cold
air along coastal north Alaska, where below normal temperatures
are possible next week. The Panhandle and coastal areas west to
the Aleutians may see temperatures near normal in periods of
clouds and showers (but below normal highs on cloudier days).
Petersen
No significant hazards are expected over Alaska during this
forecast period.
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
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