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000
FXAK67 PAJK 192250
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
250 PM AKDT Sun Aug 19 2018

.SHORT TERM...Our ridge of high pressure over the eastern gulf
continues to provide us with pleasant weather today. Sky
conditions are currently mostly clear throughout all of SE Alaska,
and with temperatures in the mid to upper 60s and relatively
light winds, outdoor activities are highly encouraged today.

By Monday, this pattern is expected to change for some locations.
The deep upper level trough over the western gulf will begin to
lift northeast, shifting the right jet region to be over the NE
Gulf Coast, namely Yakutat. This will aim the advected moisture
directly over the Yakutat area. We`ll see rain chances
subsequently increase here. However, despite the ridge weakening
as the low lifts, it will be slow to push out, leaving an
opportunity for most of the panhandle to have another pleasant day
in store for tomorrow. Based on 850 mb temperature analysis, it
may even be a warmer day for some areas down south, with
temperatures hovering around the 80 degree mark in places like
Ketchikan, Hyder, and Annette. Models do show the marine layer
moving into areas like Gustavus and Elfin Cove by tomorrow
morning. Current satellite imagery shows the marine layer just
offshore this afternoon, but forecast soundings show wind veering
to be out of the west-southwest by early tomorrow morning,
increasing onshore flow in these areas.

As the low continues to weaken and lift northeast on Tuesday,
higher rain chances will pivot to northern areas in the
panhandle. Precipitation amounts do not appear to be as
substantive as the previous day`s amounts over the NE gulf coast.
An associated weather front will also move east through the
eastern gulf then quickly weaken. This will act to increase winds,
albeit briefly, along the inner channels and increase the cloud
cover for most locations. Temperatures will be cooler on Tuesday
due to this increased cloud cover, precipitation, and onshore
flow.

.LONG TERM.../Tuesday through Saturday/...A sharply defined,
negatively tilted upper level trough will be situated over the
western gulf at the start of this long range forecast period. The
trough will rotate north and the trough axis will pass over
Southeast Alaska by Tuesday afternoon. Very strong upper level jet
support and vigorous mid level vorticity will strengthen a weather
front that is forecast to bring heavy rain to the northeast gulf
coast area Tuesday and Tuesday night. Current 24 hour rainfall
total for the northeast gulf coast ranges from 1.65 inches in the
Yakutat area to as much as 3 inches west of Icy Bay. Rain will
spread south and east through the day and night Tuesday, but the front
will weaken rapidly as the parent low weakens over south central
Alaska and the front loses favorable jet support. As the low
weakens and fills and the front moves out of the areas, high
pressure will build in over the gulf from the south on Wednesday.
Models are indicating that a short wave trough will ride up over the
top of the ridge on Thursday evening, mode agreements on this feature
is currently very poor with GFS being by far the most aggressive
in terms of PoP. For now, have left the forecast for the latter
half of the upcoming week as a very broad brushed high end chance
to low end likely for the probability of rain.

The low associated with the front on Tuesday will be weakening as
it approaches from the southwest. Thus, have only small craft
winds associated with the front over the gulf. Residual ridging
over the panhandle should result in very little wind on the
inside at first. Gradient pinching as the filling low tracks
inland and off to the east will result in a stronger southerly
pressure gradient over the far northern inner channels. Small
craft winds are anticipated over Lynn Canal Tuesday night through
Wednesday afternoon.

Daytime highs for the week are looking to be seasonable, ranging
from the upper 50s to mid 60s. Overnight lows will trend a few
degrees warmer than normal for late August owing to the expected
cloudiness associated with first the front and then the short wave.

Used a blend of GFS and ECMWF for updates to pressure through
Tuesday night with GFS as the foundation for wind speeds. PoP and
QPF from GFS for the same timeframe. Temperatures adjusted using
GFS and ensemble MOS. Overall forecast confidence is average.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ022-052.
     Small Craft Advisory due to Seas for PKZ041>043-051-053.

&&

$$

JJV/Fritsch

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