Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
635 PM EST Mon Jan 03 2022
Valid 12Z Fri Jan 07 2022 - 12Z Tue Jan 11 2022
...Overview...
As a persistent upper high over northeastern Russia finally
reorients itself more west-east and retreats westward during the
medium range period, this will lessen its influence on Alaska and
allow for lower mid-upper heights to come into the state, with a
busy storm track near the Aleutians and the northern Pacific/Gulf
of Alaska. This will favor increasing moisture and brisk winds
into southern parts of Alaska from the Aleutians late this week
into Southcentral Alaska and the Panhandle by the weekend into
early next week.
...Guidance Evaluation and Preferences...
Model guidance particularly in terms of the ensemble means
continues to show good consensus with the overall pattern, though
with some typical model differences in the details. There is good
predictability for the upper high over northeast Russia to shift
west away from Alaska through the period. Meanwhile a strong
shortwave is forecast to drop east of the high on Friday and round
underneath the retreating ridge (also serving to push the high
away) and retrograde westward across the mainland around Saturday.
Additionally, a closed low moving eastward south of the Aleutians
late week could interact/merge with that feature over the
weekend/next Monday. This interaction potential remains somewhat
uncertain, but guidance generally ends up showing a closed
mid-upper low over or near the Aleutians by Monday-Tuesday. At the
surface, the initial shortwave tracking south will likely result
in a cold front pushing through eastern parts of Alaska late in
the week, while possibly multiple surface lows spin in the
northern Pacific/Gulf and bring precipitation chances to southern
Alaska. Model guidance is incredibly variable with timing,
strength, and placement of these surface lows, but at this point
no clear outliers stand out.
For the initial part of the medium range period, went with a
deterministic model blend of the 12Z guidance somewhat favoring
the ECMWF. Ended up with a 50% deterministic/50% ensemble mean
blend by the end of the period after gradually increasing the
components of the GEFS and EC ensemble means, which served to
maintain some strength of features but blend out particular model
variations. This provided good continuity from the previous
forecast.
...Weather/Hazard Highlights...
Precipitation during the latter part of the workweek will be
generally limited to light to locally moderate rain/snow over the
Aleutians to Kodiak Island, while much of the mainland should see
dry conditions given periods of high pressure encroaching from the
north. One exception over the mainland could be light snow showers
for far northeastern Alaska as a weak surface cold front slips
through northwest Canada on Friday. Then by next weekend, a warm
front is currently forecast to push toward or into the Gulf
stemming from low pressure over the northern Pacific, increasing
moisture and potentially spreading rain/snow into Southcentral
Alaska. The increase in moisture should also interact with the
temperature gradient/stationary front along the Panhandle and
bring possibly heavy precipitation there by the weekend into next
Monday.
Given the cold surface high pressure encroaching into Alaska,
below normal temperatures remain forecast for the mainland
especially south of the Brooks Range, gradually trending less
extreme with time and may moderate to slightly above normal by
early next week as the high retreats. After a chilly period during
the short range for the Panhandle, potentially setting daily
records for cold temperatures, below average temperatures should
continue there through the end of the week with offshore flow, but
also become closer to/above average as warmer/moist inflow comes
in as next week begins. Meanwhile, the North Slope could see above
normal temperatures Friday but then should cool to below normal.
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