Area Forecast Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33
000
FXAK67 PAJK 220045
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
345 PM AKST Tue Feb 21 2017

.SHORT TERM...An active but minimal impact weather pattern for
the region over the next 24 hours. Satellite imagery this
afternoon showing a rather weak low off the northeast gulf coast
tracking southward. As this feature moves by the eastern coast an
upper level trough currently over the AK panhandle will shift
east as the stronger trough will cross into the southern
panhandle. During the early morning and into the day Wednesday an
upper level ridge shifts across the gulf then over the panhandle,
moving out the previous upper trough. By late afternoon another
upper level trough moves over the northern gulf, but this time the
associated surface low and front are expected to stay intact and
move further inland.

Scattered rain showers are moving over the panhandle coast this
afternoon, and as cooler air aloft moves in these showers will
begin to mix with some snow. Showers will remain just along the
coast and parts of the southern panhandle under the upper level
trough before clearing out tonight. Inland areas at most getting
some high and mid level clouds, but no precip expected. For
Wednesday as the upper level ridge moves in overnight skies will
clear until the afternoon low moves in with increasing clouds and
next chance for precip. Still expect only scattered showers from
this next wave but greater chance of these showers making it
further inland. Models have been inconsistent with the pop field
so low confidence in the eastward extent. With any shower
activity little in the way of precip accumulation anticipated.
Cold air advection will drop overnight lows a few more degrees
compared to last night for locations not under cloud cover.

Generally light northerly winds overnight will have a
quick shift to the south tomorrow as the gulf low moves in before
shifting back north. North gulf winds around the low center
Wednesday afternoon are expected to pick up to 25 to 30 kt with
barrier jet formation but these will be over a limited area.

12z model run showed the Wednesday afternoon wave moving in bit
faster than previous models with pop coverage further east. Enough
of a spread decided to keep pops at chance or lower inland. Used
a blend of GFS/NAM for wind and pressure with less NAM for pop.
Forecast confidence is average.

.LONG TERM...The pattern of upper level troughs/waves moving
through looks to persist into the extended forecast. Generally,
there is a large scale upper level ridge over the gulf with troughs
moving over the top of it, then progressing SE along the outer
coast of the panhandle. We have one of these passing by Wed
evening, Saturday morning, and Mon/Tues. Each one of these will
have a surface low reflection with showers making it a little
further inland each time. Expect winds through the inside waters
to flip S-SE ahead of each wave or be light and variable, then
turn back to the dominant N-NWLY flow behind them.

The Saturday morning low/trough looks to have the most likely
chance of showers reaching further inland. The upper level flow
backs a bit more onshore with that wave. Thinking that this will
be snow showers to start mixing with rain in the afternoon, so
not expecting more than an inch of accumulation at this time.

Between each system the clouds part to allow for fair weather and
some sunshine. Expect normal highs for this time of year, in the
mid 30s for the central/northern panhandle to low 40s across the
south. Partly to mostly clear skies at night will make for a
larger diurnal range with lows also near normal or slightly
below.

Made minor adjustments to this forecast package as models remain
in good agreement with inherited. For small changes preferred the
GFS. Forecast confidence is average.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ052.
&&

$$

PRB/Ferrin

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


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.