Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
656 PM EST Mon Dec 23 2019
Valid 12Z Fri Dec 27 2019 - 12Z Tue Dec 31 2019
...Below average temperatures persist over much of Mainland
Alaska...
...Stormy pattern across the Gulf of Alaska...
Upper ridging over eastern Russia and between Hawai'i and
California will support a positively-tilted trough from around 50N
south of the Aleutians into the Gulf of Alaska for the last
several days of December. With an upper low slowly lifting away
from the Beaufort Sea, well below average temperatures will only
gradually moderate but remain colder than average over the
interior. The exception will be for the Panhandle with above
average temperatures in a wet pattern.
The models continued to struggle with the timing and track of the
embedded systems in an otherwise well-modeled longwave pattern.
The ECMWF has been the most stable of all deterministic models,
but even it has showed variability larger than typical. Utilized a
method of removing the most different models which led to
inclusion of several current and previous cycles as well, as the
newer 12Z guidance did not shift in unison. 12Z GFS was not
favored past Friday as it was well northwest with a sfc low
nearing Kodiak Saturday rather than the consensus to the east. The
next system near 180 by then actually was well-clustered until it
stretched ENE Sunday with the triple point low racing into the
Gulf. Strong SW flow makes the ECMWF depiction certainly plausible
while the 12Z GFS again seemed too far to the NW (into Bristol Bay
by late Monday). Utilized more than 50% ensemble means as the 12Z
GEFS mean and 00Z ECMWF ensemble mean were fairly close but rather
devoid of detail.
The coldest days will likely be this Fri-Sun with lows in the -50s
in the colder sheltered spots south of the Brooks Range. Into
Southcentral, highs may struggle to reach zero in Anchorage while
temperatures into the 40s will be common across the Panhandle from
Juneau southward. Rainfall (and snowfall) will be quite heavy
across the Panhandle given the nearly steady storm track--several
inches of liquid equivalent will be possible over the 5-day
period. Some models show upwards of 10 inches though this may
center just south of the southern Panhandle.
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
Hazards:
- Heavy precipitation across much of the Alaska Panhandle, Thu,
Dec 26 and Sat-Mon, Dec 28-Dec 30.
- Heavy precipitation across portions of the southern Alaska,
Sun-Mon, Dec 29-Dec 30.
- Much below normal temperatures across portions of mainland
Alaska, Fri-Mon, Dec 27-Dec 30.
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