547
FXAK02 KWNH 072358
PMDAK

Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
757 PM EDT Tue May 07 2024

Valid 12Z Sat May 11 2024 - 12Z Wed May 15 2024

...Low pressure will bring moderate to locally heavy precipitation
to the southern coast this weekend, spreading into Southeast early
next week...


...Overview...

A mean trough aloft atop Alaska will be persistent through late
week into early next week, with some embedded energies including
an upper low shifting across the Alaska Peninsula into the Gulf
this weekend supporting a surface low as well. These features are
likely to produce some moderate to heavy rain and high elevation
snow from the eastern Aleutians Friday into the Alaska Peninsula
and Kenai Peninsula for the weekend and eventually into Southeast
Alaska. Precipitation may be less significant for the latter area
but could last multiple days.


...Guidance Evaluation and Preferences...

Model guidance is agreeable with the mid-upper trough expanding
from the westward part of the Mainland into the rest of it into
next week. Models even show better than typical agreement in the
energies embedded within the trough into the middle part of the
period. First a closed upper low with a stacked surface low should
push across the Alaska Peninsula into the Gulf over the weekend
and stay over the Gulf while weakening. Then additional energy
dropping south from the Bering Sea across the Aleutians during the
weekend and into the north Pacific by Monday should positively
tilt the southern portion of the trough. By Monday-Tuesday there
is a bit of spread with a shortwave or possibly small closed low
atop Bristol Bay or nearby, with the 12Z GFS weaker and farther
east. But overall, the model guidance was in good enough agreement
for a blend of the 12Z deterministic runs early on with small
incorporation of the GEFS and EC ensemble means by the mid-period.

The most uncertain feature looks to be upstream, with potential
for a closed upper low to track from Siberia into the Bering Sea
approaching Alaska by next Wednesday or so. The timing and
strength of the 06Z and 12Z GFS and the ECMWF were different but
within typical spread in the upper low and associated surface low,
but the 12Z CMC became out of phase as it took energy eastward
more quickly in the form of an open trough. The flat ensemble
means and the spread in the ensemble members themselves yield low
confidence in these features, so this will continue to be
monitored as it could be impactful to western Alaska later next
week. With the increasing model spread, increased the ensemble
mean proportion to just over half by the end of the extended
period.


...Weather/Hazards Highlights...

For Friday into the weekend, upper and surface lows tracking
across the eastern Aleutians into the Alaska Peninsula toward the
Gulf will lead to rainfall across that region and Kodiak Island
and the southern coast. Typically favored areas of onshore/upslope
flow could see heavy amounts, while higher elevation areas can
expect snow. Winds could be gusty especially for Cook Inlet into
the Gulf on Saturday ahead of the low (helping to bring in
moisture), while moderate to brisk winds are possible behind the
low as well. As the lows weaken over the Gulf, moist flow will be
directed into Southeast Alaska for the first half of next week.
The heaviest amounts there will likely be Sunday-Monday but still
may be below hazards criteria. Some lighter precipitation in the
form of rain showers and higher elevation snow showers could
extend into the Interior as well. Western Alaska may see
precipitation chances and winds increase for the middle of next
week, but with considerable uncertainty.

The unsettled pattern will tend to keep diurnal temperature ranges
more narrow than climatology, with daytime highs most likely to be
below normal and morning lows averaging above normal.  However,
some pockets of modestly above normal highs may be possible over
the Interior, while various locations depending on the day may see
slightly below normal lows.


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

$$