Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
616 PM EST Sun Mar 01 2020
Valid 12Z Thu Mar 05 2020 - 12Z Mon Mar 09 2020
...Overview and Guidance/Predictability Assessment...
The most recent model guidance continues to advertise average to
above average agreement and continuity for the synoptic features
during the days 4-8 Thursday-Monday period across the region. An
amplifying upper trough, anchored by a closed low likely to be
tracking near the Kenai Peninsula very early Wed, should progress
southeastward with time and encourage a similar path for one or
more surface lows over the Gulf of Alaska/Northeast Pacific. 12Z
guidance now has trended toward a deeper surface low offshore
southeast Alaska at the start of day 4 (Thursday). That system is
quickly replaced by upper level ridging and a brief window of high
pressure before another deeper shortwave trough approaches the
Aleutians and southern Bering Sea. Model guidance then has
converged on the idea that the upper level energy and surface low
diverts southeastward late in the week and early next weekend.
Following that period, there is reasonable agreement that an
anomalously deep upper level low moves into the portions of the
Bering Sea with deep southwesterly flow through the Aleutians. At
the surface, a fairly deep low is forecast to move across the
northern Bering Sea toward St. Lawrence Island and across the
western mainland.
The WPC blend leaned heavily on the deterministic runs of the 12Z
ECMWF/UKMET/GFS/CMC for day 4-6 where there was excellent
agreement and run to run continuity. Beyond that time frame, given
increasing model spread, higher inclusion of the 12Z GEFS mean and
00Z ECENS mean was incorporated, but there was still some
considerable weights of the 12Z ECMWF/GFS included through day 8.
...Weather Highlights/Threats...
Corresponding to the progress of low pressure over the
Gulf/northeastern Pacific, precipitation over the southeastern
corner of the mainland and Panhandle should gradually decrease in
coverage and intensity from northwest to southeast during the
latter half of the week. An area of precipitation and brisk winds
will accompany the system expected to affect the Aleutians/Bering
Sea and parts of the Alaska Peninsula around Thu-Fri. The system
likely to track into the western/northern Bering Sea next weekend
should bring a broad shield of moisture and large area of brisk to
strong winds across the Aleutians/Bering Sea and eventually into
the mainland. Some locations in the southwestern half of the
mainland will see the best potential for focused precipitation by
the latter half of the weekend. The change in pattern over the
course of the period will lead to a pronounced warming trend from
initially well below normal temperatures. The North Slope region
should be first to see readings rebound to the above normal side
of the spectrum, followed by warmer air spreading from west to
east over central/southern areas.
Rausch/Taylor
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