Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
652 PM EST Fri Nov 29 2024

Valid 12Z Tue Dec 03 2024 - 12Z Sat Dec 07 2024

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

...Overview...

Today's models and ensembles reasonably maintain the theme of the
large scale pattern evolution.  Expect a blocky configuration with
a mean upper low wobbling over the Aleutians/North Pacific while
Panhandle/western Canada upper ridging extends farther northwest
through the mainland and possibly beyond after midweek, replacing
an initial mainland col region/shortwave axis.  The main upper low
and surrounding shortwave impulses will support multiple surface
lows between the Aleutians/North Pacific and the western Gulf of
Alaska, but with widely varying amounts of guidance spread
depending on the system.  At least the overall pattern will likely
support a prolonged period of wet/snowy weather along the southern
coast and Panhandle, with some unsettled conditions extending back
into the Aleutians, and a pronounced warming trend over much of
the state.  Most of the mainland should be within the gradient
between high pressure over the Arctic and the surface lows to the
south.

...Guidance Evaluation/Preferences...

During Tuesday-Thursday, most guidance clusters around three
systems of interest.  One is the southern Bering Sea/Aleutians
deep-layer low dropping into the North Pacific.  Recent GFS runs
have been persistent in being a deep extreme with the upper low
and overdone with surface low depth (12Z GFS by at least 10 mb). 
At least the model has been trending toward established consensus
for the path of the system, so a minority weight as part of a
multi-model solution is an option today.  The new 18Z GFS run has
finally trended closer to other guidance with a more moderate
strength of the surface low as of early Tuesday.  Farther east,
there continues to be a majority signal for a system tracking
northward toward the Alaska Peninsula/western Gulf of Alaska from
early Tuesday into early Wednesday with a frontal system extending
to its east.  The 12Z CMC looks too slow while the 12Z CMCens/00Z
ECens better depict this system than the 12Z GEFS mean.  Recent
machine learning (ML) models offer reasonable support for the
majority scenario.  Then a trailing mid-latitude Pacific system
may track northward to a position near or a little south of the
eastern Aleutians by early Thursday.  Dynamical and ML guidance
generally agree with this scenario.  Meanwhile there is a better
signal today that the initial Aleutians low may maintain
definition into Thursday as it rotates underneath the just
aforementioned system.  This part of the forecast incorporated a
blend consisting of 40 percent 12Z ECMWF, 20 percent each 12Z
GFS/UKMET, and 20 percent total 12Z CMCens/00Z ECens.

From later Thursday through Saturday, dynamical/ML models
increasingly diverge for exact upper level details and surface
systems within a somewhat more agreeable mean pattern consisting
of an axis of relatively low heights near the Aleutians (a
combination of earlier upper low/shortwave energy and eventually
additional dynamics that arrive from the west) and elongated
ridging that persists over the mainland.  There is also an
emerging western Pacific system likely to track south of 50N by
Friday-Saturday.  A considerable dynamical/ML majority keeps this
system far enough south to have minimal influence on the
Aleutians.  The increasing detail differences led to splitting the
40 percent ECMWF component between the 12Z/00Z runs plus
increasing the total ensemble mean weight to 40 percent (with some
12Z GEFS included at this point).  This solution emphasizes the
most agreeable larger scale themes, and in particular the Thursday
system near the eastern Aleutians weakening thereafter while
another system may track toward the eastern Aleutians/Alaska
Peninsula Friday into Saturday. 

As for other considerations spanning these two parts of the
forecast, the slow northward solution of the CMC with the early
system leads into other northern stream energy combining with it
to yield more upper troughing near the western coast and more
associated surface low pressure.  Some GFS runs before 12Z had
hinted at such a trough axis but ML models favor a pattern more
like the ensemble means and other dynamical guidance fitting their
solution.  Also of note, today's guidance consensus is somewhat
stronger with the upper ridge extending across the mainland after
midweek.

...Weather/Hazards Highlights...

The overall pattern continues to look favorable for episodes of
enhanced precipitation from the Alaska Peninsula to the Panhandle
next week, with generally southerly mean flow aloft between an
upper low/trough over the Aleutians-North Pacific and an upper
ridge over the Panhandle/western Canada (eventually through the
mainland).  Multiple surface systems directed by the upper flow
should help to focus the activity, with the most likely surface
low tracks directed toward or near the Alaska Peninsula/eastern
Aleutians with associated fronts extending to their east.  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.  Currently most guidance suggests that a majority of
this precipitation will remain below hazardous thresholds, though
multi-day accumulations may still end up being significant.  There
is a somewhat better defined signal for focused precipitation over
the southern Panhandle on Tuesday with the first system initially
south of the Alaska Peninsula, so the Days 3-7 Hazards Outlook
depicts a heavy precipitation area for that day.  Nearby time
frames could also have enhanced totals but with guidance a little
more mixed than seen at this time yesterday.  Rainfall may produce
enhanced runoff and rises on area rivers.  Expect unsettled
conditions but with lighter precipitation over the Aleutians. 
Most of the mainland north of the Alaska Range should remain dry
next week.  One or more of the surface systems could generate
areas of brisk to strong winds.   

The northern three-fourths of the state will be on the cold side
with below normal readings into Tuesday, including some overnight
lows in the -20s over far eastern interior areas.  Then aside from
valley locations where cold air typically persists longer, the
overall pattern will support a pronounced warming trend with time.
 Most areas should see above to well above normal temperatures by
the end of the week with anomalies for min temperatures generally
a little greater than those for highs.

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