Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
659 PM EST Mon Mar 03 2025
Valid 12Z Fri Mar 07 2025 - 12Z Tue Mar 11 2025
...A couple of low pressure systems may bring enhanced
precipitation and gusty winds into coastal areas of Alaska late
this week into early next week...
...Overview...
An upper trough stretching from much of the Mainland into the
northeast Pacific at the start of the period Friday will gradually
make its way east over the weekend. Ahead of this upper trough, at
least one surface low and moist Pacific inflow should allow for
precipitation to spread across Southeast Alaska through late week,
and enhanced winds are possible especially over maritime areas
depending on the details of surface lows. The mean southerly flow
will also lead to widespread above normal temperatures. The upper
trough pushing through should then flip the pattern, cooling
temperatures closer to normal and lessening precipitation amounts.
Into next weekend, mean upper ridging will track through the
Aleutians/Bering Sea into the northeast Pacific, while another
upper/surface low moves into the Bering Sea behind it and spreads
winds and precipitation first to the Aleutians, and toward the
western and southern Mainland early next week.
...Guidance Evaluation and Preferences...
Model and ensemble guidance is in generally good agreement with
the pattern described above, especially early in the forecast
period. Guidance struggles more with the smaller scale details of
the embedded vort maxes and surface lows though. By Friday, recent
models are still supporting a possibly moderately deep surface low
in the northeast Pacific, with some placement and depth spread
that could affect wind forecasts. GFS/GEFS members still hint at a
separate low farther west in the vicinity of Kodiak Island, and
the WPC forecast shows that secondary low initially as a frontal
wave. There is also model spread in how fast the low weakens over
the weekend; today the ECMWF is the slowest to do so. The WPC
forecast tried to take a middle ground approach with the low
position, which trended a bit closer to the coast Friday-Saturday
compared to yesterday's forecast.
Models are in good agreement in principle with that trough
deepening and shifting east, while an upper ridge pushes through
the Aleutians Friday-Saturday. There is more spread over the
weekend with the northern part of the ridge as models have varying
solutions with how much energy may track in from the Arctic and
disrupt it over the Interior. Behind the ridge, there is fairly
good consensus upstream for an upper low and potentially a strong
surface reflection to move across the Bering Sea this weekend and
early next week. What becomes more uncertain is how much energy
ejects east toward the Gulf versus how much is held back into the
Bering Sea early next week. The ECMWF and its ensemble members are
much more focused on energy staying in the Bering rather than
moving east, and this is confirmed by looking at cluster analysis,
though using the 00Z ensemble guidance that is on the older side.
The GFS suite allows for more vorticity to track east and a
surface low to form in the Gulf. The ECMWF-based AIFS and the
GFS-based Graphcast both were actually even stronger than even the
GFS with an upper low developing farther east. So tended to lean
toward the GFS suite with the troughing potential in the Gulf and
vicinity, with the support of at least some AI guidance. The
pattern upstream gets even more complicated with the potential for
another low or trough to come across the Kamchatka Peninsula and
impact the Bering Sea pattern.
The WPC forecast favored a blend of mainly deterministic models
early in the period. As the period progressed, increased the
proportion of ensemble means (with a lean toward the GEFS mean) to
half by Day 6 and more Days 7-8 with the increasing model spread.
...Weather/Hazards Highlights...
Moderate to locally heavy precipitation will be moving into
Southeast Alaska into Friday with likely a more consolidated
surface low in the northeast Pacific. Some modest precipitation
may wrap into Southcentral as well. Precipitation chances, at
least for enhanced amounts, are forecast to slowly lessen into the
weekend as the trough aloft pushes through. The northern Pacific
and vicinity surface lows may also cause periods of moderate to
strong winds for the Gulf and perhaps even spreading into coastal
areas Friday-Saturday. The details will depend on uncertain
surface low magnitudes and tracks.
Periods of light to moderate snow are possible farther north
across much of the Interior through late this week. Additionally,
northerly flow on the backside of the lows may produce gusty winds
channeling through the Bering Strait to St. Lawrence Island and
possibly cause some maritime hazards or perhaps localized blizzard
conditions into Friday. The deep layer northerly or northwesterly
flow is also likely farther south across the Aleutians to Alaska
Peninsula Friday-Saturday behind the trough, which could cause gap
winds in favored areas. By the weekend, the next low approaching
the Aleutians will lead to strong southerly winds and
precipitation chances there ahead of the low's cold front, with
potentially strong westerly winds behind. By early next week
precipitation chances could spread into the Alaska Peninsula, Y-K
Delta, and into Kodiak and the Kenai Peninsula as upper/surface
lows may set up in the Gulf.
Most of Alaska will remain much milder than normal through Friday,
though starting to moderate compared to the short range period.
Cooler than average temperatures could start to come into western
Alaska with the first trough aloft, and spread across much of the
state over the weekend with the northerly flow behind the trough.
Some central and eastern areas could remain slightly above normal
despite the relative cooling. The upper ridge behind the first
trough could allow for temperatures to shift to above normal by
5-10F in the western Mainland and temperatures a few degrees on
either side of normal in eastern Alaska.
Tate
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