Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
641 PM EST Wed Jan 15 2020
Valid 12Z Sun Jan 19 2020 - 12Z Thu Jan 23 2020
...Overview...
Upper-level ridging over the the North Slope and northwest Canada
will quickly move north and east allowing for longer period of
upper-level troughing to setup over the North Pacific Ocean into
the Gulf of Alaska. This pattern will remain mostly in place
during the extend period thanks to a fairly progressive North
Pacific/Aleutians/Bering stream. This synoptic pattern favors
warming across southern Alaska initially along with focused
precipitation over the Panhandle and westward to around the
eastern part of the Kenai Peninsula with one or more northeastern
Pacific/Gulf waves. The Aleutians should see some light
precipitation through the weekend, followed by the possible
arrival of an organized area of moisture associated with a North
Pacific system by mid-week.
...Guidance/Predictability Assessment...
Model guidance continues to be in general agreement with a mean
trough extending from eastern Siberia to the Gulf of Alaska and
multiple lows traversing eastward; however, the timing and
latitudinal differences mentioned with the previous forecast
package have yet to resolve. A compromise of the 12Z ECWMF/GFS
with light weighting of the their ensemble means provided an
acceptable solution. This combination also helped maintain a sense
of continuity in regards to a compact upper low tracking
north-northwest between Siberia and the western mainland that may
interact with separate upper low/trough energy that approaches
from the west. Another feature of note is fairly strong system in
the North Pacific that may bring an increase in clouds and
precipitation to portions of the Aleutian Chain by the middle of
next week. Again, there continues to be significant spread with
the specifics and confidence on the timing and amplitude are at or
below average at the time of this issuance. With lower confidence
of the evolution by the end of the forecast period, weighting of
the ensemble means increased for days 5-7.
...Weather/Hazards Highlights...
Warmer temperatures are expected this weekend across much of
southern and southeast Alaska, moderately from below normal. A few
locations may actually rise to above normal, particularly near the
southeast Mainland region. Above normal temperatures will also be
in place for the North Slope and surrounding locations this
weekend. Periods of scattered to widespread precipitation will
likely focus from the eastern Kenai Peninsula to the Panhandle
from Sun into next week as one or more waves reach the Gulf;
intensity may become moderate to heavy. The Aleutians will see
light to isolated moderate precipitation through the weekend into
early next week, followed by uncertain coverage/intensity of
organized precipitation depending on the track of the system to
the south.
Campbell
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
- Much below normal temperatures across portions of mainland
Alaska, Sat-Mon, Jan 18-Jan 20.
- Much below normal temperatures across portions of the Alaska
Panhandle, Sat, Jan 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