Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
524 PM EST Sat Jan 11 2020
Valid 12Z Wed Jan 15 2020 - 12Z Sun Jan 19 2020
...Overview...
Upper ridging and a closed high will migrate across the North
Slope late next week as the cold remains over eastern/southeastern
portions of the state. Milder air will push into
western/northwestern areas as height rise in advance of a
weakening Bering system. Precipitation will be below average with
a suppressed storm track.
...Guidance/Predictability Assessment...
The 12Z GFS/ECMWF and somewhat the 12Z Canadian offered reasonable
clustering with the 00Z ECMWF ensemble mean and 12Z GEFS mean to
start the period, Wed-Fri, with high pressure shifting into the
Yukon. GFS did differ from the ECMWF/Canadian with a wave of low
pressure along the front that should race northward Wednesday over
the western Aleutians. By Fri, GFS again started to be on the
quicker side of the spread with a system south of the Aleutians,
so its weighting was decreased as elsewhere it seemed reasonable.
The Canadian departed from the ensemble consensus late Fri well
south of the area with that low pressure system. By next weekend,
uncertainty exists in its track, dependent upon the upper pattern
to the north/northwest.
Across the mainland/interior, ensemble trend was in the direction
of the ECMWF 24 hrs ago with a farther north movement of a closed
high into the Beaufort Sea and perhaps toward Banks Island by the
end of the period. This would open the door for lower
heights/upper low to slip westward underneath the upper high
across Southcentral, bringing in another cooler air mass. Ensemble
consensus was preferred as the upper pattern lends itself to
uncertainty in timing/location of the upper features.
...Weather/Hazards Highlights...
Much of eastern/southeastern Alaska, especially the Panhandle,
will have lingering much below normal temperatures as arctic high
pressure ~1040mb only slowly retreats into NW Canada. To the west,
with increased southerly flow, milder air will lift northward and
push somewhat eastward as upper heights rise west of about 150W in
advance of the dying Bering system. Precipitation will be light
given the storm track well to the south, focused over the
Aleutians (heavier farther west), the western/southwestern
coastline, and over Kodiak and the southern Kenai peninsula. Late
in the period, the northeast Pacific system may track toward the
southern Panhandle, but considerable spread exists.
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