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Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
247 PM AKDT Thu May 28 2020

.SHORT TERM...

Through Saturday night...A familiar summertime synoptic weather
pattern grips Southeast Alaska through this weekend bringing
spotty rain showers (mainly across the south and coast), seasonal
to warmer than normal temperatures, and periodic breezes
interrupting light winds.

The pattern features a relatively strong low nested in the
central Gulf of Alaska. The low will go absolutely nowhere as the
only hope for its removal is a jet currently streaming in the
western Pacific just offshore of Japan. A series of short-waves
rotates counter-clockwise about the low, each passing across
Southeast Alaska. Unfortunately, our forecasts depend on the
track, timing, and strength of these shortwaves. While, on water
vapor imagery, one can time and follow them and correlate
rainfall accumulations and breezy conditions by their arrival,
all of these elements become steadily more difficult in time. As
each feature is weak and causes very little surface reflections in
our marine observation network, they are certainly poorly
resolved by numerical models as well. For this reason, the
forecast through the weekend strives mainly for mean conditions,
rather than trying to grab any peaks. If we were to discern any
identifiable trends that could contribute value, we note that the
low weakens over time. Therefore, isolated to scattered showers
Friday appear to be less expansive Saturday and are slightly less
likely to occur.

With clearer skies and offshore flow over Upper Lynn Canal,
Skagway and Haines both reached the lower 70s today. With more
moisture slated to spread north, we do not expect such lofty
afternoon temperatures as today on Friday and Saturday. In fact,
the bulk of the Panhandle stayed between 55 and 65 degrees. Thus,
we are expecting repeats into Saturday as synoptic conditions
will have barely changed.

While the Inner Channels should be free of hazards, we are
expecting small craft easterlies across the gulf waters through
Friday. Winds through Inner Channel communities will largely stay
light, with periodic breeziness as passing waves enhance winds at
the surface.

Forecast confidence is low on details, but higher on overall
synoptic pattern.

.LONG TERM.../Sunday through next Thursday night/ As of 10pm
Wednesday. The barotropic low that has been lingering in the Gulf
for several days will persist through Saturday. By Saturday night,
model guidance begins to weaken this feature, ultimately washing
it out into a trough on Sunday. This weakening should increase the
PoP chances to the north as the offshore flow breaks down. Winds
out in the Gulf can also be expected to slow down as the pressure
gradient around the low weakens. Flow turns onshore across the
panhandle and should prime the entire region for pretty decent
chances for rain Sunday afternoon and through the first part of
next week. Heaviest rain ATTM looks to occur on Tuesday as a front
associated with another low moves toward the region from the
southwest. While models seem in pretty good agreement regarding
the timing of this frontal band, the actual strength of it is
still a bit too early to determine with reasonable certainty. It
is of note though that the potential for some fairly significant
precip amounts and impactful winds does exist with this system.
Onshore flow continues for the duration of forecast period
continuing chances for precip across the panhandle. High
temperatures during the forecast period will be slightly below
normal during the forecast period, but with limited diurnal swing
at night due to persistent cloudy conditions.

Forecaster's model of choice was a blend of GFS/ECMWF and then a
lean towards WPC guidance to maintain continuity. Forecast
confidence that the period will be wet is above average.
Confidence in the wind forecast is less the average, particularly
for the Tuesday front.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ022-041>043-051>053.

&&

$$

JWA/JDR

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