Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
627 PM EST Wed Feb 17 2021
Valid 12Z Sun Feb 21 2021 - 12Z Thu Feb 25 2021
...Overview and Guidance/Uncertainty Assessment...
Higher predictability features next week will be an upper low
meandering near Banks Island in the Canadian Archipelago and upper
ridging in the mid-latitudes south of the Gulf of Alaska. This
will maintain wavy westerly flow across the Aleutians into the
Gulf/Panhandle enhanced by a shortwave or weak upper low swinging
through Southcentral late Sun into early Mon (and the Panhandle
late Mon into early Tue). To the west, the ensembles remain
unstable and separated in timing, becoming out of phase (GEFS vs
ECMWF EPS vs Canadian ensembles) as early as next Monday. Still
prefer to side with the quicker group of the guidance, with
support from the 12Z ECMWF/Canadian/UKMET rather than the slower,
but not implausible, GFS. This did modify some timing of incoming
systems but the large uncertainty out of northeastern Asia makes
this tough to remain consistent day to day. Utilized an increasing
weight of the ECMWF ensembles to prevent large future changes. By
the middle of next week, possibility exists for a defined system
to move north-northeastward into the Gulf (ECMWF/Canadian) but
downplayed this newer scenario for now.
...Weather/Hazards Highlights...
System into the Gulf early Sunday will yield modest to perhaps
locally heavy rain/snow over the Panhandle followed by showery
precipitation Monday as the upper trough moves through.
Thereafter, weaker systems in the flow will produce generally
light rain/snow to the Aleutians and into southwestern Alaska as
they progress eastward, generally tracking through the Gulf.
Moisture may attempt to spread into/through the Tanana/Yukon
Valley around the middle of next week, though the ECMWF remained
most bullish with this scenario.
Well below normal temperatures are likely for much of the Interior
and into Southcentral Sun-Mon as sub-500 dm heights rotate through
the Alaska Range. The North Slope and Panhandle will see near to
below normal temperatures through the period. Some moderation is
forecast over the Aleutians to southwestern Alaska by the middle
of next week as heights rise in advance of troughing in the far
western Bering Sea. Temperatures may be 5-10 degrees above normal
over the Y-K Delta into the AKPen.
Fracasso
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle,
Sat-Mon, Feb 20-Feb 22.
- Much below normal temperatures across portions of mainland
Alaska, Sat-Tue, Feb 20-Feb 23.
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