Small Craft Advisory 429, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
225 PM AKDT TUE JUN 14 2016

.SHORT TERM...Area will be under NE flow aloft between an upper
low to the NE and an upper ridge to the NW. There will be several
shortwave trofs moving into the area through Wed. The most
significant shortwave trof will move toward the far SE panhandle
Wed afternoon. At the surface...a low pressure trof will extend W
into the central panhandle by late tonight and remain there into
Wed. A weak warm front over the S yukon into the NE gulf coast
will dissipate tonight. High pressure will build over SE interior
AK and the S Yukon late tonight and Wed. Models were in good
agreement on the large scale NE flow and surface features but did
have some differences with some of the shortwave trofs...except
there was good agreement on the shortwave trof moving toward the
SE panhandle Wed.

Main forecast concerns will be precip potential...cloud
cover...winds...and temps. Currently...only precip around the area
is over the NE gulf coast near Yakutat. This is associated with
the weak warm front there. This precip will rapidly diminish this
evening as the front dissipates. There may be some showers over
the far N and near Hyder associated with a couple shortwaves. The
shower threat will diminish over the N overnight as one shortwave
moves offshore...while the shower threat over the far SE will
spread slowly W into the S inner channels as a shortwave moves
into that area tonight. Then...after a break...the more
significant shortwave moving toward the SE panhandle Wed afternoon
will increase shower threat again. This one will have some colder
air aloft with some warm advection in lower levels. Forecast MU
CAPES in that area will exceed 1000 J/KG in the afternoon...which
will increase threat for TSTMS mainly for the NE half of the Hyder
zone Wed afternoon.

Bands of high and mid-level clouds will move across the area from
the NE tonight...with the most concentrated clouds over the far N
and SE with shortwave trofs. Other main cloud source will be
marine layer clouds over the E gulf and outer coast. These clouds
will spread SE along the S outer coast tonight...then decrease
from the NW over the N half of the coastal area late tonight and
Wed as low level flow becomes more offshore.

Strongest winds will be in the E gulf coastal waters...with 20-25
KT NW winds expected tonight. This wind band weakens a bit on Wed
and will be pushed a bit offshore. Will also have 15-20 Kt NW
winds over the S inner channels tonight that will diminish late.
Over the N...local effects currently dominate with 10-15 KT winds
in many areas. By late tonight...a more northerly pressure
gradient will shift flow to N-NW over most of the northern inner
channels...with 15-20 KT winds likely by late tonight. Strongest
winds over the N will be in northern Lynn Canal late tonight and
Wed morning. Some decrease in the N flow will occur Wed afternoon
as local effects begin to affect the wind field.

Much warmer temps will be the rule over the N half of the area Wed
with offshore flow and decent amount of sunshine likely. 925 mb
temps are forecast to rise into the 15-20C range...with the
warmest temps in the downslope region of the NE Coast Mtns. Most
areas over the N will get well into the 70s...with a few 80s
possible over the far N. The S will have more cloud cover and
lower level flow will turn more southerly...so max temps there
will be held in the 60s.

.LONG TERM...A surface trough of low pressure extending E-W from
Canada will remain over the central panhandle Wednesday night into
Thursday. Expect partly cloudy to mostly sunny skies for the next
few days and highs in the 70s for a large portion of the area.
Majority of showers will remain on the Canadian side of the
Coastal Mountains, but a few may make it over. Have continued with
a chance or slight chance in the forecast, namely over the
southern border area of Hyder. Thursday night, high pressure will
start to build from the south and shift winds through the inside
waters to a southerly direction. The ridge will continue to build
over the Eastern Gulf Friday into Saturday. There is potential for
a marine layer to develop over the Eastern Gulf late Thurs into
Friday with the developing ridge. This will need to be monitored
for more clouds getting into the nearby coastal areas.

On Sunday a front will approach from the west, but be slowed down
and weakened by the ridge. Most models have rain moving over the
northern panhandle by Monday morning then spreading south through
the day. Have increased POPs up to likely where models agree, but
there are slight timing and intensity differences for the rainfall,
so there is lower confidence in that part of the forecast.

&&

.HYDROLOGY...The reported water level in Suicide Basin has been bouncing
up and down for the past day or so. A new sensor was being installed
by USGS so hopefully the data coming in smoothes out. Still no sign
of an actual release into Mendenhall Lake as it continues to fall
slowly this afternoon. However...we will continue to monitor this
closely.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ041-042.
&&

RWT/Ferrin

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