Gale Warning 158, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
249 PM AKDT Sat May 20 2017

.SHORT TERM.../Through Sunday night/Low pressure over the central
gulf will move slowly N, while another low develops and moves N
into the gulf Sun. The second low will merge with the first low
over the NW gulf by Sun evening. Strong occluded front will move
to the outer coast by Sun morning, then pass through all except
the southern Panhandle by Sun evening. Used blend of the 12z GFS
and NAM to handle things through Sun night.

Main forecast concerns will be precip intensity/amounts and
winds. Strong low level jet, anomalously high precipitable water
values, and jet support aloft will make for locally heavy rainfall
in many areas. Initially, most of the area should see locally
heavy rain with occluded front offshore tonight. As front moves
onshore Sun, the rain rates will drop off over the north and
central area by Sun afternoon, while the south remains in locally
heavy rain with front hanging up over them. The NE gulf coast may
see some locally heavy rain even behind the front for a few hours
Sun due to good upslope low level flow. Currently thinking a
general 2 to 4 inches of rain with locally higher amounts should
occur through Sun night, with the higher amounts over the south.

Winds have picked up to gale force over the gulf ahead of the
front. As the front moves through, winds should drop off over the
gulf some, but second low moving in Sun will pick them back up
some. Over the inner channels, strongest winds will be over the
south and central areas with mainly SCA level winds expected with
some gales in Clarence Strait. The far N area will be somewhat
lighter tonight but pick up Sun as front moves through, so Lynn
Canal will likely see SCA level winds Sun into Sun night.

.LONG TERM.../Monday thru Saturday/as of 10 pm Friday...Monday
starts out with a super long fetch from the SW pouring into SE
Alaska starting around 30N. The surface pattern on Monday is not
strong but enough to develop SE wind 10 to 20 KT over an already
big sea outside. All 20/00Z ops models support this scenario. On
Tuesday there is also good agreement that a negatively tilted
shortwave will dig into the Eastern Gulf with cool but not cold
air aloft. This will be the last gasp of a very wet few days at
which time we should see rivers in many areas subsiding. The good
news is that a mondo upper ridge will build over the central Gulf
by early Wednesday. This will support a surface ridge offshore for
low level onshore flow. Look for clearing especially inland on
Wednesday with moderate westerlies developing. This has all the
signs of a marine push up against the coast later in the week and
enhanced sea breezes. Best guess is dry Thursday through Friday
then it gets really uncertain as to the upper ridge kicking out
East or not.

&&

.AVIATION...VFR conditions across most of the panhandle this
afternoon but rain has started and ceilings and visibilities have
started to lower. Expect many areas to drop to MVFR and IFR
conditions this evening and overnight as rain intensifies with
lower conditions continuing into tomorrow. Winds and LLWS will
also be a problem for much of tonight and tomorrow, particularly
for the southern panhandle and outer coast.

&&

.HYDROLOGY...Rainfall of 2 to 4 inches with locally higher amounts
is expected through Sun night. Think highest rainfall will be
over the south where more prolonged heavy rain is expected with
front hanging up over them. Should be enough rain to help raise
water levels to near bankfull levels especially over the central
area by Sun evening. Later shifts will need to monitor this
closely.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Gale Warning for PKZ036-041>043-051-052.
     Small Craft Advisory for PKZ012-013-021-022-031>035-053.

&&

RWT/JC

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Special Weather Statement
National Weather Service Juneau AK
253 PM AKDT Sat May 20 2017

AKZ017>029-220000-
Cape Fairweather to Cape Suckling Coastal Area-
Taiya Inlet and Klondike Highway-Haines Borough and Lynn Canal-
Glacier Bay-Eastern Chichagof Island-
Salisbury Sound to Cape Fairweather Coastal Area-
Cape Decision to Salisbury Sound Coastal Area-
Eastern Baranof Island and Southern Admiralty Island-
Juneau Borough and Northern Admiralty Island-
Inner Channels from Kupreanof Island to Etolin Island-
Dixon Entrance to Cape Decision Coastal Area-
Southern Inner Channels-Misty Fjords-
Including the cities of Yakutat, Skagway, Haines, Gustavus,
Hoonah, Elfin Cove, Pelican, Sitka, Port Alexander, Angoon,
Juneau, Petersburg, Wrangell, Kake, Craig, Klawock, Ketchikan,
Metlakatla, and Hyder
253 PM AKDT Sat May 20 2017

...Heavy rain likely this weekend into early next week...

A strong frontal system has moved into the Gulf of Alaska this
weekend and is expected to remain there through Monday. This
front will bring widespread rain, which will be heavy at times
Saturday night through Monday. Rainfall amounts of 2 to 4 inches
are expected with locally higher amounts possible. Heavy rain for
the entire panhandle, with the heaviest rain is now expected over
the southern panhandle. This rainfall will cause rises on area
rivers and streams, and it is possible some smaller streams and
rivers may reach at least bankfull level by Sunday night. Stay
tuned to later forecasts and possible statements for updates on
this developing situation.