Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
628 PM EST Sun Nov 14 2021
Valid 12Z Thu Nov 18 2021 - 12Z Mon Nov 22 2021
...Much below normal temperatures likely across Alaska through the
medium range period...
...Overview and Guidance Evaluation/Preferences...
An expansive and blocky upper ridge over Russia should keep the
Alaska region storm track along/south of the Aleutians and into
the Gulf during the extended range. A deep upper low centered over
the Gulf on Thursday will weaken as it retreats into Canada by
Friday, although general troughing should linger across central
and southern Alaska through the weekend. To the West, another deep
low will translate south of the Aleutians and into the Gulf by
early next week.
The 12z GFS, ECMWF, and CMC show reasonable agreement with the
large scale pattern for a purely deterministic model blend days
4-5/Thursday-Friday. After this, the typical detail uncertainties
begin to arise, particularly regarding a few reinforcing
shortwaves rounding the base of the Aleutians low and lifting
north from the north Pacific. To help mitigate these harder to
resolve details, WPC blended more of the ensemble means for the
late period. The GFS and ECMWF however show enough agreement with
the ensemble means to maintain at least modest amounts of those
models in the blend, which should provide some needed additional
definition/depth to individual systems. This approach also
maintains good continuity from yesterdays forecast.
...Weather/Hazard Highlights...
Precipitation over Alaska should be confined to the
Aleutians/Southern Coast/Panhandle, with much of the mainland
remaining very cold and dry, other than maybe a few snow showers.
Low pressure in the Gulf on Thursday-Friday will continue to bring
a period of moderate to locally heavy precipitation to much of the
Panhandle region. In addition, favorable flow funneling through
the mountain ranges of southern Alaska may result in the potential
for localized but strong outflow winds into Thursday across
downwind locations of southeast Alaska. A system into the
Aleutians late this week should bring unsettled conditions to the
region with light to moderate precipitation spreading towards the
Peninsula and Southern Coast as well. Enhanced precipitation
should again move into the Panhandle by next weekend as the next
low pressure system approaches.
Much below normal temperatures should prevail across much of
Alaska, especially the central and southern regions, through next
week as surface high pressure becomes established across the
state. The most pronounced anomalies should be over the western to
southern part of the state where daytime highs could be as much as
20-30+ degrees below normal. Temperatures should remain below
normal into next weekend, but may moderate slightly as the upper
trough weakens and upper ridging attempts to sneak in from the
west. The exception to this will be the North Slope, where
temperatures should remain closer to normal through next weekend,
though a brief period of modestly above normal temps are possible
Friday and Saturday.
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
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