Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
554 PM EDT Sat Oct 17 2020
Valid 12Z Wed Oct 21 2020 - 12Z Sun Oct 25 2020
...Guidance/Predictability Assessment...
Upper ridging is forecast to move into western coastal Alaska from
the Bering Sea by midweek next week, blocking much of the Interior
from significant precipitation until perhaps next weekend. The 12Z
guidance showed decent agreement to start the period Wed-Thu
though the 12Z GFS/ECMWF were closer to the ensemble means than
the Canadian/UKMET. Differences remained with how to handle a
northern central Pacific system next week with some trends to a
bit farther south initial position Wed-Thu but then a farther
north position next Fri-Sat. By that time, ensembles showed a
large amount of east-west spread (GEFS west, ECMWF ensembles
father east) as the surface low should move eastward just south of
the Aleutians but then turn northeastward due to more ridging into
the Gulf than previously forecast. In light of the recent
uncertainty, trended to just the 00Z ECMWF ensemble mean for next
weekend as it was between the quicker ECMWF and slower/west GFS
and GEFS. This was only a bit to the northeast of the forecast
yesterday.
...Weather/Threats Highlights..
Upper ridging will bring above normal temperatures to much of the
western coastal area and Interior, especially over the North
Slope, with dry conditions. Temperatures may be 10-15 degrees
above normal along and north of the Brooks Range, and 5-10 degrees
above normal north and west of the Alaska Range. Areas of
eastern/southeastern Alaska and especially the Panhandle will see
near to below normal temperatures as high pressure (around 1040mb)
delivers easterly flow to the region. Rainfall will be confined to
the Aleutians initially, then spreading across coastal
Southcentral areas into southwestern Alaska as the Aleutian system
moves along the island chain and perhaps toward Bristol Bay. It
will be rather breezy over the southern Bering and Aleutians due
to the tightening pressure gradient between mainland high pressure
and the low pressure system.
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