Scientific Forecaster Discussion
fxak67 pajk 172235
Southeast Alaska forecast discussion
National Weather Service Juneau Alaska
235 PM akdt Sat Aug 17 2019
Short term...current satellite gives a fairly good depiction of
the low pressure system currently moving along the southern coast
of the Panhandle. Rain has been a bit heavier than previously
forecast with some areas reporting in excess of an inch, mainly
between the far eastern Inner Channels and the coastal mountain
range. This will continue to be the focus for highest precip
totals as the low continues it's trek to the south. Satellite also
gives a pretty good look at an area of scattering out/clearing
behind the furthest north boundary of the precipitation, further
evidenced by observations at paya, pagy, and pahn. Expect this
trend to continue going into the late afternoon where pajn may get
an opportunity to see at least some sun late in the day.
Regardless of the precipitation, the main feature of this system
will be the wind. As the low moves north, it will continue to
deepen which will cause a sharp increase in the pressure gradient.
Winds through the north-south oriented channels, where they
haven't already will begin to swing around to the north and begin
to become quite strong. This is already bringing high Small Craft Advisory
criteria to Lynn Canal where winds tonight will increase briefly
to storm force criteria. Winds will continue to increase through
the night in a multitude of other channels as well with gale force
winds expected through Frederick Sound and Chatham Strait and all
other waterways north. Gale force winds are also anticipated along
the coastal waters tonight.
On Sunday, expect these winds to slow down but still continue to
be at Small Craft Advisory into the afternoon. Most locations fall below advisory
criteria before evening with these higher winds holding on the
longest through Lynn Canal.
Aside from the more impactful weather, temperatures will also
become noticeably cooler from the above normal days we have seen
in the past couple of weeks. Also, despite being breezy in some
areas, most should get a pretty nice Sunday with sunny conditions,
mainly through the north and central Panhandle.
Long term.../Monday through Saturday as of 10 PM Friday/
upper trof will be deepening over the Gulf and NE Pacific at start
of the period. A southern stream shortwave will also come into
play, but the models differ on the timing of this feature moving
NE. This is affecting whether the northern stream trof phases with
the southern stream shortwave, and potential for a significant
low that could move into the eastern Gulf around Tue. A vast
majority of the 12z GFS ensembles suggest there will be a
significant low moving into the eastern Gulf (with some
timing/strength differences noted) Tue or Tue night. The position
of the main upper trof west of 140w also supports a system moving
into the eastern Gulf. For this reason, decided to introduce a
developing low moving north-northeast into the eastern Gulf for Tue-Tue
night forecast periods. For the Mon-Mon night periods, used blend
of GFS/European model (ecmwf) to handle things as they were fairly close. After
Wed, decided to leave things as is due to increasing model
differences out that far, and current forecast looks reasonable at
that time frame.
Have brought in a period of gale force winds to the southeast Gulf Tue
into Tue night, with gales possible on back side of the low over
the central Gulf as it reaches peak intensity. Inner channel winds
could potentially get to gale force as well. Could be a
significant rain event, especially across the southern half of the
area, based on a forecasted low track into the north-central
Panhandle. After this system moves out, next system looks like it
will move in from the SW for late week, but model differences with
it make for a low confidence forecast.
public...strong wind through Sunday morning for akz025.
High Wind Warning from 7 PM this evening to 6 am akdt Sunday for
Strong wind from 7 PM akdt this evening through late tonight for
Strong wind until 1 am akdt Sunday for akz018.
Strong wind from late tonight through Sunday afternoon for
Marine...Storm Warning for pkz012-013.
Gale Warning for pkz021-022-031>034-042-043-051.
Small Craft Advisory for pkz011-035-041-053.