Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
753 PM EDT Thu Aug 17 2023
Valid 12Z Mon Aug 21 2023 - 12Z Fri Aug 25 2023
...Overview...
An Arctic low looks to meander north of the state next week,
supporting a frontal system or two pushing into northern Alaska.
Farther south, a parade of lows across the northern Pacific is
possible as the period begins Monday, with one pushing into
British Columbia, one farther west that should stay south of the
state, and another south of the Aleutians. This last low looks to
be most impactful to Alaska, as the upper and surface low features
are forecast to track northeastward crossing the Aleutians through
the eastern Bering Sea and into the southwestern Mainland as the
week progresses. This will maintain an upper troughing pattern
over the Bering and into the western part of the state, which
could bring in moist southwesterly flow and rain chances, with
enhanced totals possible generally from the Seward Peninsula into
the Brooks Range into the latter part of next week (after an event
in the short range period also affecting that area).
...Guidance Evaluation/Preferences...
Model guidance is in fairly good agreement with the pattern
described above, considering the lead time. There are some
remaining differences with the Arctic upper low track. Models
mostly meander it north of Siberia early in the week and then with
a gradual loop northeast later in the week. The 06Z GFS and the
12Z EC were among the faster ones to track it east compared to the
12Z CMC and GFS. An in between solution seemed to work, which
keeps the center of the low well north of Alaska but with
uncertainty edging into the North Slope. Then in general today's
models are more agreeable with a low track northeast across the
Aleutians/Bering, helping develop/maintain troughing there. The
12Z GFS is among the farther west solutions with the low track
though, and (perhaps related) maintains more ridging into
Southeast Alaska than other guidance that show troughing pressing
into more of the mainland. Uncertainty remains with how far inland
the trough axis makes it and the timing of its progression east.
Lessened the weighting of the GFS with time but maintained some
ECMWF and CMC in the blend as the period progressed, while
increasing amounts of the GEFS and EC ensemble means to about half
by the end of the period.
...Weather/Hazards Highlights...
Precipitation across the northwestern Mainland is likely to be
ongoing on Monday, with some enhanced rainfall possible as a front
draped across the northern tier may provide some added focus, and
favored windward terrain in the Brooks Range may see relatively
higher totals. While this event should produce meaningful
rainfall, totals are currently not expected to reach hazardous
thresholds. Amounts are forecast to lighten by Tuesday, but rain
chances should increase once again Wednesday-Friday as the
upper/surface lows move across the Aleutians/Alaska Peninsula into
the Mainland along with moisture streaming in. Generally the
western half of the state will be most affected, with totals once
again likely enhanced from the Seward Peninsula to the western
half of the Brooks Range, though with uncertainty in the low
track, this lowers confidence in the exact amounts.
The northern mainland should see the greatest negative anomalies
for high temperatures during the period, though the coastal
communities may stay warmer than average. The eastern interior and
southern Panhandle will see the best potential for above normal
highs. Low temperatures look to be more above normal, with just
scattered pockets of modestly below normal anomalies.
Tate
No significant hazards are expected over Alaska during this
forecast period.
Additional 3-7 Day Hazard Information can be found on the WPC
medium range hazards outlook 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