Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
658 PM EST Fri Nov 12 2021
Valid 12Z Tue Nov 16 2021 - 12Z Sat Nov 20 2021
...Overview and Guidance Evaluation/Preferences...
Shortwave troughing sliding across the Alaska Peninsula to start
the period on Tuesday will interact and merge with amplified
troughing dropping south across the Mainland. This will maintain
troughing and a well defined surface low in the Gulf of Alaska
through the remainder of next week and weekend. Elsewhere, another
low pressure system will translate east well south of the
Aleutians as the next deep low drops into the vicinity of the
western Aleutians by late next week. This will send another
deepening surface low pressure system west and south of the
Aleutians Friday and Saturday.
For days 4-5/Tuesday-Wednesday, the guidance shows reasonable
enough agreement to allow a general deterministic model blend
between the GFS, ECMWF, and CMC. After this, the models begin to
diverge with the typical timing and detail differences regarding
shortwave energy into the Gulf and also reinforcing energy/surface
low south of the Aleutians next Friday-Saturday. The biggest model
concern is the 12z ECMWF made a somewhat significant continuity
jump as its much quicker to eject troughing/closed low energy
across the Mainland into western Canada and tries to rebuild
ridging over western Alaska by next weekend, bringing the warmer
air mass in too quickly. It also presents increased differences
with the next system into the Aleutians, keeping the surface low
much farther north than the better consensus/ensemble means. The
12z GFS and CMC are much more in line with the ensemble means, as
is the previous run (00z) ECMWF. As such, the WPC forecast used
the 00z ECMWF in place of the 12z run through the entire period,
with more emphasis towards the ensemble means the second half of
next week to help mitigate the uncertainty.
...Weather/Hazard Highlights...
Much of the precipitation over Alaska should be confined to the
Aleutians/Southern Coast/Panhandle, with much of the mainland
remaining dry and cold, other than maybe a few snow showers.
Precipitation should accompany a cold front, spreading eastward
from the Panhandle/Southern Coast to the Peninsula region on
Monday into Tuesday. Southerly flow ahead of the weakening cold
front into the Gulf will bring a period of moderate to locally
heavy rainfall to much of the Panhandle Wednesday into Thursday,
with wet but lighter intensity precipitation lingering the rest of
the week associated with low pressure in the Gulf. The next system
into the Aleutians should bring another round of unsettled
conditions to the region with light to moderate precipitation and
gusty winds for the western Aleutians and north into the Bering
Sea.
Below to much below normal temperatures should prevail across much
of Alaska (with the exception of the North Slope region) through
next week as surface high pressure becomes established across much
of the state. The most pronounced anomalies should be over the
western and southwestern part of the state where daytime highs
could be as much as 15-30 degrees below normal. The north slope
should begin above normal, but quickly moderate back closer to
normal the rest of the week.
Santorelli
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
Hazards:
- Much below normal temperatures across portions of mainland
Alaska, Mon-Thu, Nov 15-Nov 18.
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