Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
648 PM EST Sat Nov 30 2024

Valid 12Z Wed Dec 04 2024 - 12Z Sun Dec 08 2024

...Wet/snowy pattern for the southern coast and Panhandle during
the upcoming week...

...Overview...

The average of model and ensemble guidance remains fairly
consistent and agreeable with a large scale pattern evolution
featuring persistent Panhandle-western Canada mean ridging aloft
extending northwestward through the mainland after early Wednesday
while incoming dynamics eventually elongate North
Pacific-Aleutians mean upper troughing after one or more upper
lows wobble around/south of the Alaska Peninsula.  This pattern
will favor multiple episodes of precipitation along/near southern
coastal areas and the Panhandle while promoting a trend to above
normal temperatures across most of the state.  However individual
surface lows continue to be very sensitive to lower-predictability
shortwave details, so some forecast details still have low
confidence.  There is better consistency with the idea of the
mainland staying within the gradient between these surface lows
and Arctic high pressure.  A larger scale mid-latitude Pacific
system may approach the Alaska Peninsula by next Sunday and
hopefully it will have somewhat better predictability.

...Guidance Evaluation/Preferences...

As of the start of the period early Wednesday, there is at least
some consistency with the idea of upper dynamics and associated
surface system reaching near the Alaska Peninsula with a frontal
system extending to its east.  There has been a fair degree of
spread and variability for the exact strength and longitude of low
pressure, with latest guidance generally showing a deeper trend
for the 12Z Wednesday valid time.  Most dynamical and machine
learning (ML) models generally show one or two more waves tracking
northward to or beyond the Alaska Peninsula later in the week. 
While there has been some trending toward the potential for at
least one of these waves to track farther west/northwest into the
Bering Sea than previously forecast (including from dynamical and
latest ML runs), at differing valid times the CMC and GFS lean to
the more extreme side of the spread in that regard.  Thus far, not
enough ensemble members depict such a scenario to pull their means
very far away from the Alaska Peninsula.

Over the past day or so most guidance has been trending stronger
with a trailing mid-latitude Pacific system forecast to track a
ways south of the Aleutians Friday-Saturday.  The latest majority
cluster of models/means would have this system track northeastward
thereafter, reaching near the Alaska Peninsula by next Sunday.  ML
models have exhibited some spread but the new 12Z runs seem to be
clustering a little better and generally support a system in the
realm of the model/mean average for track (perhaps a tad faster)
with an intermediate depth between the ensemble means and deep 12Z
GFS/00Z-12Z ECMWF.

Through most of the period, random dynamical/ML solutions have
been showing potential for additional wave development farther
east of the above primary systems, with some influence on the
Panhandle and vicinity.  Preference continues to be to downplay
the definition of these waves until guidance shows better
agreement.  Finally, in varying ways the 12Z GFS/UKMET in
particular (CMC weaker) show potential for Arctic shortwave energy
to approach the far northern mainland by around Friday. 
ECMWF/ICON runs and ML models are not enthusiastic about such a
shortwave and the new 18Z GFS has trended noticeably northward.

Today's forecast maintains the continuity of the general pattern
aloft while refining some details, though the more sensitive
surface low details have adjusted a little more.  A blend of
00Z/12Z ECMWF runs and 12Z GFS/UKMET/CMC for about the first half
of the period reflected detail refinements where some agreement
existed while downplaying the more uncertain smaller-scale
specifics.  The forecast quickly adjusted toward a nearly even
model/ensemble mean (12Z GEFS/CMCens and 00Z ECens) mix next
weekend to emphasize the consensus pattern evolution and guide
toward an intermediate depth of the Pacific to Alaska Peninsula
system.

...Weather/Hazards Highlights...

Expect continuation of multiple episodes of enhanced precipitation
from the Alaska Peninsula to the Panhandle midweek into next
weekend given moist southerly mean flow aloft between general
troughing/upper lows over the Aleutians-North Pacific and an upper
ridge over the Panhandle/western Canada through the mainland.  A
number of surface systems supported by features aloft should help
to focus the activity.  The most likely surface low tracks
mid-late week should be directed toward or near the Alaska
Peninsula with associated fronts extending to their east, but
there is lower-probability potential for some waviness to reach
farther east and affect the Panhandle (extending into the
weekend).  Coastal and nearby low elevations should tend to see
rain, with snow elsewhere.  Milder conditions over the southern
Panhandle will likely yield broader coverage of rain with snow
confined to higher elevations.  The majority of this precipitation
will remain below hazardous thresholds at most locations but
higher localized totals are possible and multi-day accumulations
may still end up being significant.  These systems could produce
periods of brisk to strong winds as well.  Expect unsettled
conditions but with lighter precipitation over the Aleutians
through late week.  A potentially vigorous Pacific system may
increase precipitation and winds over the eastern Aleutians/Alaska
Peninsula by next weekend, most likely Sunday.  Most of the
mainland north of the Alaska Range should remain dry or see only
scattered light snow.

The forecast transition toward multiple days of above to well
above normal temperatures remains on track.  Expect anomalies to
increase from south to north, with North Slope locations finally
flipping to above normal for next weekend after staying somewhat
below normal into late week.  Some valley locations where cold air
typically persists longer may also take a while to trend above
normal.  Anomalies for min temperatures should generally a little
greater than those for highs, with highest departures from normal
tending to be over the south.

Rausch

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