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FXAK67 PAJK 231448
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
648 AM AKDT Wed Aug 23 2017

.SHORT TERM.../Wednesday through Thursday night/As of 0600, an
upper level shortwave is beginning to lift out of the eastern gulf
through the SE Alaskan panhandle this morning. The main front
that was associated with this circulation has already made its
push through the region, and we can see it on WV satellite exiting
into British Columbia to our east. The precipitation we`re
currently seeing across the panhandle is due in part to the trough
of warm air aloft, generated as the extra-tropical low matured to
occlusion stage. We also had some clearing earlier due to drier
air wrapping around the circulation, but that appears to have
ebbed as the precipitation continued to move in at the head of the
circulation from the gulf. Winds were relatively calm throughout
the night, but we`ve seen some areas pick up speed this morning,
especially in the southern panhandle. We`re expecting the winds to
stay relatively strong in the southern panhandle and along the
eastern gulf waters in along the southern panhandle because of a
tight pressure gradient that has set up over that area.

A ridge of high pressure should begin to build in behind the
shortwave and eventually spread over the panhandle once the low
exits today. Precipitation should clear out, for the most part,
across the panhandle through Thursday, and winds should also
decrease as well. By Thursday afternoon, another front will begin
to push northeast across the eastern gulf as another shortwave
begins to dig into the gulf and progress east. Precipitation will
again make an appearance as that front moves through the
panhandle.

Relatively little change was made to the forecast. Wind speeds
and directions were adjusted for detail in specific inner
channels. PoPs were also adjusted using ensemble blends. We`ve
also kept a small area for slight chances of thunderstorms along
the marine zone from the Dixon Entrance to Cape Decision, as there
was some support from CAPE with relatively high lapse rates
around 6.8 degrees Celsius for elevated convection. We`ll monitor
this area as the day progresses.

.LONG TERM.../Friday through Wednesday/ Upper level low will have
dropped over the Aleutian chain into the western gulf then
broadening over the central and eastern gulf through Saturday. By
Sunday this low will track north while weakening as high pressure
builds over the panhandle and eastern gulf through late Monday.
Another upper low forms over the western gulf by mid week, however
its interaction with the high pressure ridge and eventual track
is uncertain. At the surface frontal band will have moved into
the panhandle with rain across the entire panhandle. Series of
surface waves rotating under the upper low will move over the
panhandle Friday into Saturday before starting to diminish on
Sunday. Heaviest rain fall likely to occur Friday night into
Saturday morning. More model spread starting Sunday with the
position of the surface features. ECMWF a more northerly low
track and faster drying trend for the south while GFS moves low
center much further south with higher rainfall amounts there. This
variation lasts into Monday, but by Tuesday operational models
fall more in line with high pressure over the panhandle keeping
most fronts/precip off to the west. Small craft winds along
frontal bands for Friday with chance for narrow bands of gales.
Due to uncertainly into Sunday kept with a broad brush approach to
wind fields.

Inherited forecast and new model runs for Friday and early
Saturday will still in line so little change was made. Due to
large operational spread starting Sunday kept with WPC ensemble
approach, which also showed little variation from previous runs.
Initially higher confidence but this quickly drops through the
weekend.

&&

.AVIATION...Some MVMC conditions will arise in the southern
Panhandle with showers from the low offshore, but conditions
should improve later tonight. IMC conditions are largely not
expected.


&&

.HYDROLOGY...The big event is over from the atmospheric river
stemming from the remnants of Banyan. All streams are either
cresting or falling. But high levels persist this morning. Some
heavier showers today may slow falls today in Ketchikan, but
speedier falls will occur tonight.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ035-036-041>043.

&&

$$

Voveris/PRB

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