Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
752 PM EDT Sun Mar 13 2022
Valid 12Z Thu Mar 17 2022 - 12Z Mon Mar 21 2022
...Overview...
The most notable feature over Alaska for the medium range period
will be an upper low meandering slowly southeastward over the
Alaska Peninsula as the period begins Thursday, shifting into the
Gulf of Alaska through late week. A potent upper-level shortwave
diving southward across the Bering Sea as well as energy along an
active storm track across the northeastern Pacific will serve to
redevelop and reinforce the closed low through early next week.
This pattern will support a series of surface low pressure systems
and bring a sustained period of inclement weather through the
Panhandle and occasionally up into the southern coasts for much of
the week.
...Guidance/Predictability Assessment...
Overall model guidance has rather good agreement for a medium
range Alaska forecast throughout most of the period. The upper low
appears well handled by the guidance as an initially closed system
over the Alaska Peninsula Thursday, with some question of whether
it will be open or closed during a transition period on Friday as
it begins to interact with potent energy dropping south across the
Bering Sea. A multi-model blend of the 12Z deterministic guidance
(GFS/ECMWF/CMC/UKMET) worked well for days 4-5, with the blend
serving to smooth out the relatively small individual model
differences. The feature is likely to close off once again over
the weekend as energy consolidates, though with some differences
in its position (how far east/west) Saturday as it drifts. Then
guidance now has the core of the low retrograding back west of
Kodiak Island by Sunday due to additional energy interaction from
the northeastern Pacific, and hovering Monday over the Gulf. The
overall meandering and energy interactions aloft as well as the
associated surface low pressure systems vary somewhat from model
to model, but this general idea is the same amongst guidance with
clear outliers not really seen for today's forecast. With these
minor differences, the WPC forecast phased in some of the GEFS/EC
ensemble means while maintaining some operational guidance in the
blend for strength of systems for the latter part of the period.
The overall trend looks to be slower/farther west with the upper
low lingering by days 7-8 compared to yesterday, as the northern
Pacific energy serves to reload the low.
...Weather/Hazard Highlights...
Much of the mainland should see dry conditions during the period,
though perhaps with increasing snow showers by next weekend in the
eastern mainland, as precipitation is expected to focus along
southern parts of Alaska given the northern Pacific storm track.
The Panhandle in particular should see rounds of enhanced
precipitation, with the heaviest amounts in the medium range
period currently expected on Friday with the deepest of the Gulf
surface lows. The precipitation will linger across the Panhandle
with rounds of increasing and decreasing intensity depending on
location of the surface lows and the orientation of the upper
trough/low--so Saturday could see a relative lull before amounts
pick up early next week. While precipitation does not appear to be
very intense, recent heavy rain/snow across the area could make it
more sensitive to additional impacts. In addition, brisk winds are
expected with the approach of Friday's surface low with some gusty
winds possible across the Panhandle. On the other side of the
lows, periods of breezy northerly winds are expected over the
Aleutians, along with some chances of snow showers.
Colder than average high temperatures are forecast for much of
Alaska given troughing aloft, with highs generally 10-20F below
normal for mid-March across the southwestern mainland and Alaska
Peninsula on Friday and Saturday as a reinforcing cold front comes
through. These cooler temperatures will spread into much of the
interior as well. However, low temperatures should be closer to
normal with some areas even above normal for lows. The North Slope
will be the main area that can expect near to above normal
temperatures for highs as well as lows, along with possibly the
southeastern mainland. Meanwhile, the Panhandle should see below
normal highs through the period and a mix of above and below
normal lows.
Tate
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