Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
533 PM EST Sun Dec 01 2019
Valid 12Z Thu Dec 05 2019 - 12Z Mon Dec 09 2019
...Heavy rain/snow possible for southern coastal areas late this
week into the weekend...
Upper ridging will meander in the East Siberian Sea toward the
North Pole, favoring troughing to its south from Kamchatka
eastward through the Bering next Thu-Mon. This will take an
initial Bering system in a couple waves eastward to deepen around
Saturday before translating into the Gulf. Slow movement this
coming weekend may favor locally heavy rain/snow for areas around
Cook Inlet. Its eastward progression is a bit of a question, as
the broad expanse of the upper trough suggests sfc wave
development along the front that will slow is movement toward the
Panhandle. In the interior, cold high pressure will slowly shift
into Canada after a couple cold nights.
Multiple low centers in the Bering suggest a consensus approach,
but using mostly 12Z deterministic models. This should coalesce
into a deeper system by Fri/Sat as the front continues eastward.
GFS/Canadian became quicker with the front than the ECMWF, but
preferred to stay on the slower side given the broad upper trough
over the central Pacific that suggests trailing height falls to
help induce sfc wave development along the front and likely slow
its progression. Ensembles seem to favor this scenario too, but
confidence was no higher than average since small timing changes
in the near term can amplify differences by 7-8 days out.
Downstream CONUS pattern (building western ridging into BC) should
favor a slower timing as well.
Precipitation will focus over the Aleutians and AKPEN initially
then expand across Southcentral where it could be locally heavy
(coastal rain, inland/terrain snow) as the triple point develops
near Kodiak this weekend. Ensemble QPF guidance highlight the west
side of Cook Inlet and southeast-facing areas of Kodiak and
especially the Kenai peninsula where 5-10" of liquid-equivalent
QPF is depicted (even a bit higher in the GFS/ECMWF).
Fracasso
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
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