Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
636 PM EDT Tue May 25 2021
Valid 12Z Sat May 29 2021 - 12Z Wed Jun 02 2021
...Periods of heavy rain likely from the Peninsula region to the
Panhandle, as well as in parts of southern Alaska...
...Overview and model guidance...
The overall pattern across Alaska for the medium range period will
feature a large scale upper level low that will move south of the
Aleutians this weekend, while a second cutoff low drifts westward
across the mainland and into the Bering Sea. The two systems
should begin to interact with each other by early next week as
upper level ridging builds back in across central and northern
Alaska. At the surface this translates to a frontal boundary
draped across southern Alaska while a series of frontal systems
affects the Peninsula, Southern Coast, and Panhandle.
The latest suite of guidance shows above average agreement on the
overall large scale pattern, but some uncertainty with regards to
details of individual perturbations around the Aleutians low and
also how the two lows may interact the second half of the period.
WPC favors a blend heavily weighted towards the deterministic runs
(GFS/ECMWF/CMC) through day 5, with increasing weighting of the
ensemble means days 6-8 to mitigate smaller scale differences. The
12z ECMWF and CMC are the closest deterministic runs to the
agreeable ensemble means so modest inclusion (30 percent total) of
those models were included late period just to give a little
pattern definition to the washed out ensemble means.
...Weather/Threats Highlights...
Energies rounding the main upper low south of the Aleutians will
send a series of frontal systems into the Gulf of Alaska resulting
in several days of unsettled weather (winds and rain) to areas
from the eastern Aleutians to the Panhandle. Models show anomalous
moisture being streamed northward into the region, with periods of
moderate to heavy precipitation. There remains some uncertainty
regarding the details and local enhancements along the coast, but
at this time, the best signal for highest totals during the
five-day period exists from the Kenai Peninsula to the Panhandle
as well as farther inland across the Alaska Range mountains (snow
in the highest elevations). Some places, especially along the
coast, could see several inches of rain from this weekend into
early next week.
The cutoff low through eastern and southern Alaska will bring
temperatures modestly below normal to start the period on
Saturday, but should steadily rebound back towards or even above
normal in some places as the low exits into the Bering Sea this
weekend. By early next week, temperatures should be near or above
normal from western regions through the central part of the state
as upper level ridging builds aloft. Meanwhile, expect below
normal temperatures to last through the entire period from the
Aleutians to the Panhandle and parts of Southern Alaska underneath
of cloudy and rainy skies.
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 the Alaska Panhandle and mainland
Alaska, Fri-Sun, May 28-May 30
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