Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
658 PM EST Fri Dec 4 2020
Valid 12Z Tue Dec 8 2020 - 12Z Sat Dec 12 2020
...Guidance and Uncertainty Assessment...
The deterministic and ensemble guidance is in relatively good
agreement that the strong Gulf low over the Gulf region during the
short-term period will be rapidly weakening by Tuesday, and also
in good agreement that high pressure north of the Arctic Coast
will keep the weather pattern cold and dry across the Interior and
North Slope region. There is greater model uncertainty with the
next strong low pressure system approaching the Aleutians by
Wednesday into Thursday, with the GFS considerably stronger and a
little to the northwest of the ECMWF through early Friday, whilst
the ensemble means are indicative of a farther east solution.
Both the ECMWF and GFS are also indicating a surface low
approaching the southeast Panhandle region, with the former being
the more impactful scenario. By the end of the week, the GFS and
ECMWF indicate a third storm system that may eventually settle
across the northern Gulf region by next Saturday. Given the
uncertainty among the deterministic and ensemble guidance for this
time range, the forecast was based primarily from a GEFS/ECENS
compromise for the Friday to Saturday time period. Some of the
12Z ECMWF and less of the GFS was used for early in the week along
with the ensemble means.
...Weather/Hazards Highlights...
An intense low pressure system is likely to approach the Aleutians
by the middle of the week. This storm is expected to produce
strong and gusty winds across the Islands and southwest Alaska
mainland, along with additional heavy rain and mountain snow
across areas that have already received heavy precipitation over
the past week. Onshore flow across the southeast Panhandle region
is also expected to produce numerous rain/snow showers on top of
already saturated grounds. Farther inland across the Interior and
the North slope region, a generally benign weather pattern is
expected with little in the way of snow and subzero temperatures
for much of the Interior and extending north of the Brooks Range.
Hamrick
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Mon-Tue, Dec
7-Dec 8.
- High significant wave heights for coastal portions of the Alaska
Panhandle and mainland Alaska, Mon, Dec 7.
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