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Area Forecast Discussion
Issued by NWS Juneau, AK

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FXAK67 PAJK 161335
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
535 AM AKDT Mon May 16 2022

.SHORT TERM...-- Changed Discussion --/Through Mon night/ Rain showers from a frontal band
moving through this morning are spread across the southern
and central panhandle up to Gustavus, Hoonah, and Angoon.
Satellite rain rate and radar imagery does show that the northern
edge of the showers is just south of Juneau as of 5 am and slowly
moving north. This band of showers should spread over the rest of
the northern panhandle by midday.

Behind it, a few more short waves are expected to move north
across the panhandle through tonight as they wrap around a
weakening low in the southern gulf keeping the area mostly damp.
The strongest one moves into the south this afternoon and has a
bit more dynamics associated with it. First off some higher
southerly winds are likely ahead of it as southerly pressure
gradients briefly tighten. Areas like Stephens Passage and Lynn
Canal will likely see a step up in winds to 20 or 25 kt this later
this morning and into the afternoon hours. Second, a mass of
cooler air aloft combined with an area of enhanced vorticity is
moving in with the short wave and is expected to destabilize the
atmosphere enough that some thunderstorms could occur across the
southern panhandle this afternoon and evening. Not a great chance
of this happening but the best chance will be in areas where some
clear breaks show up this afternoon especially along the higher
terrain.

Forecast changes were mainly focused on local effects from winds
though inner channel winds were increased for the late tonight,
Tue, and Tue night time period as stronger southerly flow still
exists from the remaining low in the gulf at that time. Otherwise
changes were mostly minor.

.LONG TERM.../Tuesday through Friday/...Major themes in the
extended range forecast are diminishing precipitation through
Tuesday night followed by decreasing clouds and significantly
warmer daytime highs for the balance of the week. Small craft
easterlies/southeasterlies over the coastal marine zones of the
eastern Gulf will persist through Tuesday night and end early
Monday morning. Although the current forecast does not have small
craft winds on the inside, it may become necessary to include them
for Clarence Strait Tuesday and Tuesday night.

At the start of this long range forecast, models are in good
agreement and depicting a large upper level low centered over the
Gulf of Alaska. This low will drop south and then be ejected east
by a 150kt jet. Strong and deep upper level ridging will then
shift east, become negatively tilted, and develop into a large
omega block. At the surface, this feature is not nearly as well
defined, but can be identified easily enough when comparing the
surface pressure pattern to the 300mb and 500mb heights.
Additionally, an inverted surface trough will remain situated over
the Panhandle for most of the coming week.

A significantly warmer continental low level airmass will move in
from the east beginning on Wednesday courtesy of the inverted
trough and this will be the basis for the warmer daytime highs
and clearing skies that Southeast Alaska will experience during
the second half of the upcoming week. Highs in the low to mid 50s
on Tuesday will be replaced by mid 60s, or possibly even higher,
by Thursday. Owing to the continental source region of this warmer
air, relative humidity values will drop as well, getting down to
the mid 30s in some places. Fortunately, green-up is well under
way across Southeast Alaska as a whole, which will act to
mitigate, but not completely, eliminate any fire danger.-- End Changed Discussion --

.AJK WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --PUBLIC...None.
MARINE...Small Craft Advisory for PKZ012-033>036-041>043.-- End Changed Discussion --

EAL/Fritsch

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