Small Craft Advisory 545, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
254 PM AKDT Sat Nov 4 2017

.SHORT TERM.../Through Monday/ High pressure over the Yukon will
move SE into BC and weaken tonight. A low pressure area will
develop over the NE Pacific and move NE into the southern gulf as
a storm by Mon morning. An inverted trof will extend from the
developing low into the N gulf Sun into Sun night then it will
dissipate by Mon morning. Weak arctic front will slide S into the
far N panhandle Mon. Generally used 12z GFS to handle system
movement/intensity but did cap some of the higher winds over the
gulf as the increase would have been significant from the previous
forecast.

Winds will generally diminish later tonight into early Sun as the
high slides SE and weakens. Winds will begin to pick up in the
more E-W channels Sun into Sun night as low develops. Gale to
storm force winds are expected over the gulf Sun night into Mon.
Many inner channel areas will see SCA to gale force winds Mon.
Currently think some land areas will need strong wind headlines at
most as pressure gradient orientation will not be favorable for
the usual windy spots that favor SE winds Mon. Most likely areas
for wind headlines will be the central/southern coast and far S
inner channels. Should see increased outflow winds over the N as
well and will need to monitor the PAGY and PAJN areas for strong
NE winds Mon.

Precip from low and inverted trof will develop over the N-central
gulf by Sun afternoon, then spread slowly E across the NE gulf Sun
night. As inverted trof weakens though, stronger offshore low
level flow will diminish the precip threat along the NE gulf
coast Sun night into Mon. Precip will spread E across the rest of
the E gulf Sun night then reach mainly the southern panhandle
Mon. However, the weak arctic front may also have a little snow
with it over the far N so keeping in some chance of precip there
as well. One concern is potential for accumulating snow especially
along E side of Baranof and SE Chichagof Islands. Think they will
remain cooler with some upslope flow there, and this may keep
precip mainly snow there. Some minor accums will be possible in
other parts of the S, mainly well inland, but not expecting any
headlines will be needed as temps will probably be above
freezing.

.LONG TERM... Monday night through Saturday...The storm we had
recently been tracking throughout the long-term period has now
moved into the last part of the short-term forecast, but effects
of this system will spill-over into the Monday night/Tuesday
timeframe with strong winds and lingering precipitation toward the
southern panhandle.

Though the distance between Yakutat and the offshore low is
relatively large, this will provide enough moisture transport to
fuel the rain/snow mix that Yakutat will be seeing first during
this system. Precip will move along the outer coast and largely
remain hovered over the southern panhandle with an inch at most
near Wrangell. As the front pushes through, gusty winds will be
affecting the inner channels. It is a little early to say at this
point, but we are learning towards the possibility of a high wind
watch for the Prince of Wales area on Monday. There should also be
decent outflow, especially near Cross Sound. Conditions are
marginal for a mountain wave event for late Monday. A large area
of warm air advection is leading the low and fueling the building
of a ridge Monday into Tuesday. We think that this ridge is acting
as a blocking system, causing lower precipitation amounts across
the central panhandle than originally thought and little eastward
progression of the system. Another surface low will build by
Wednesday.

Model consensus starts to drop off after Wednesday next week. The
WPC generally follows an average of the GFS/EC and starts with
the low centered in the northern Gulf moving south by mid-week.
Temperatures were nudged up early in the week and lowered by mid-
week (with temperatures aloft still showing -30 C temps at the
500 mb level). Models wanted to lean colder for Friday, but
variability in cloud cover and southerly winds aloft led us toward
an upward trend toward the end of the week. Early on in the
timeframe, a GFS/EC blend was used to maintain consistency with
WPC. Though the location and timing of precipitation is still
relatively uncertain Monday night into Tuesday, the largest
values of QPF will likely remain south of Kake and Petersburg.
Depending on the next model run, this could mean either rain or no
rain remaining in Sitka by Wednesday.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ012-013-022-031>034-041>043-051-052.

&&

RWT/TA/Sullivan

Visit us at http://www.weather.gov/Juneau