Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
727 PM EDT Mon Apr 03 2023
Valid 12Z Fri Apr 07 2023 - 12Z Tue Apr 11 2023
...A troughing pattern over Alaska will lead to colder than normal
temperatures across much of the mainland and wet weather from
Southcentral Alaska into the Panhandle...
...Overview...
Overall a cold upper troughing pattern is likely across much of
Alaska through late next week and into early next week, as an
upper low drifts over the northwestern mainland and a couple of
shortwave energies combine to produce another upper low in the
Gulf of Alaska/northern Pacific by the weekend as well. Meanwhile
rounds of low pressure in the Gulf of Alaska should lead to a wet
pattern for Southcentral Alaska into the Panhandle, along with
some potential for windy conditions across the southern coastline
depending on the exact low tracks.
...Guidance Evaluation/Predictability Assessment...
Model guidance appears fairly agreeable on the large scale but
with some small scale differences. The period begins Friday with
one upper low likely atop northwestern Alaska--model guidance has
all converged on this placement with the 12Z UKMET finally jumping
on board after previous runs indicated the low staying farther
north of Alaska. There are some slight differences regarding the
low position by Saturday, with the GFS runs now on the farther
north side compared to the non-NCEP guidance. Meanwhile notable
upper energy rounds this upper low's southwestern side Friday,
crossing the Aleutians/Alaska Peninsula from the Bering Sea into
the northern Pacific along with an associated surface low. Models
are indicating that this energy should form another closed upper
low farther south into the northern Pacific this weekend. There
are some remaining model differences as to the placement of the
upper low and thus with surface lows as well. Though these are
certainly within typical spread at the medium range lead time, the
variations impact the sensible weather concerns of precipitation
and winds placement that are dependent on the low tracks. No real
outliers were necessarily noted though. For early next week, the
pattern looks to slowly shift east as the northern upper low
weakens, while ridging comes in across the Aleutians first and
eventually into the southwestern mainland by around day 8/Tuesday.
The WPC forecast was based on a blend of the 12Z deterministic
ECMWF/GFS/CMC/UKMET early, with increasing inclusion of the
ensemble means by days 6-8 as model spread increased.
...Weather/Hazard Highlights...
Multiple rounds of precipitation are likely across Southcentral
Alaska and the Panhandle as surface lows and deep layer
southwesterly Pacific flow direct moisture into the region. Recent
model runs generally indicate that the Kenai
Peninsula/Southcentral may see the heaviest precipitation, but
there has been considerable variety in the placement of notable
amounts that could spread into the Panhandle. Meanwhile much of
the mainland farther inland is likely to see dry conditions after
some light snow possible across the eastern mainland into Thursday
night tapers off. The upper-level energy and surface low passing
over the Aleutians/Alaska Peninsula will cause some light
precipitation there on Friday, with some threat of windy
conditions too. Moderate to strong winds are possible over the
weekend on the backside of the Gulf lows with possibly some gap
winds in favored areas from the Aleutians east to the Kenai
Peninsula, while areas farther east could see windy conditions as
well, depending on the low tracks. Then the western mainland could
see increasing snow chances for Monday-Tuesday next week as the
pattern changes there.
Temperature-wise, the trough/low aloft will cause colder than
normal temperatures across at least western and central Alaska.
Friday-Sunday are likely to see temperatures of around 10-30F
below average in terms of lows, with departures for high
temperatures possibly even larger locally. Actual temperatures are
likely to be below 0F for lows as far south as portions of the
southwestern mainland. Meanwhile, while highs should be cooler
than normal all the way east into the Panhandle, lows could stay
warmer than average with the mild moist inflow there. Temperatures
could moderate a bit by Monday-Tuesday as the northern upper low
erodes.
Tate
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Sat, Apr 8.
- Much below normal temperatures across portions of mainland
Alaska, Thu-Mon, Apr 6-Apr 10.
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