Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
519 PM EST Mon Dec 02 2019
Valid 12Z Fri Dec 06 2019 - 12Z Tue Dec 10 2019
...Deep Lows lend a Maritime Hazard and Southern AK Tier Heavy
Precipitation Threat...
...Guidance/Uncertainty Assessment...
The 12 UTC GFS/ECMWF and 12 UTC GEFS/NAEFS/ECMWF ensembles are
reasonably well clustered and seem to offer above normal
predictability and continuity for a stormy Alaskan weather period
Friday-Sunday. A blended composite solution along with the
National Blend of Models provides offers a good forecast starting
point. Deterministic model forecast spread and uncertainty
increases rapidly by next week, lending a quick transition to a
much more compatable ensemble mean blended forecast approach.
...Weather/Hazard Highlights...
Mid-upper ridging from northeast Russia to the Arctic will favor
deep mean closed Bering Sea troughing aloft. This will support
development and reformation of several deep and stormy surface
systems over the southern Bering Sea late week and the weekend.
Slow movement favors locally heavy rain/snow downstream whose
forcing mechanisms should prove slow to progress eastward, but
eventually work across the Gulf of AK to the Southeast Panhandle
early next week with pattern transition. Meanwhile overtop in the
interior, high pressure will slowly shift into Canada after a
couple cold nights late this week.
The deep lows offshore will remain a signifciant maritime hazard
to include high winds and waves. Multiple periods of heavy
precipitation will also work onshore and focus over the
AKPEN/Southwest AK heading into the weekend and then expand across
Southcentral then Southeast AK where it could be locally heavy
(coastal rain, inland/terrain snow). This transition occurs into
next week as triple point developments focus near Kodiak Island.
Ensemble QPF guidance highlight the west side of Cook Inlet and
southeast-facing areas of Kodiak Island and especially the Kenai
peninsula where 5-10" of liquid-equivalent QPF is depicted (even a
bit higher in the GFS/ECMWF). This activity will be fueled by long
fetch and slow to translate plumes of deep lower latitude
originated moisture.
Schichtel
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
Hazards:
- Heavy precipitation for parts of the Alaska Panhandle and
mainland Alaska, Sat-Mon, Dec 7-Dec 9.
- High winds for parts of the Alaska Panhandle and mainland
Alaska, Sat-Sun, Dec 7-Dec 8.
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