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
000
FXAK67 PAJK 131530
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
630 AM AKST Wed Dec 13 2017

.SHORT TERM.../Wednesday morning through Thursday night/...The
next front to bring heavy rain to Southeast Alaska is located over
the central gulf as of this morning. Satellite imagery loops show
plentiful mid level moisture streaming north and doppler weather
radar reflectivity has increased significantly overnight. Some
locations never stopped raining from yesterday`s front. Other
spots saw a brief break, but that will end today. 24 hour totals
for today and tonight will be the greatest with more than 2.5
inches forecast for Yakutat, whereas far southern locations may
see as little as 1/2 inch. By tomorrow, the front will have pushed
inland a bit, so the highest amounts will likely be over the coast
mountains. Still, 24 hour totals for Thursday morning through
Thursday night will range from less than 1/2 inch to more than one
inch with the highest amounts over the central and southern inner
channels farthest away from the gulf. Warm air continues to be
advected north from lower latitudes, so snow levels will remain
high enough through this short term forecast period that snow will
only be a possible concern along the Klondike Highway and possibly
the Haines highway. Water levels will rise on panhandle creeks,
streams, and rivers and a Special Weather Statement has been
issued to address this. At present, only Jordan and Montana
Creeks near Juneau are forecast to reach bankfull and no flooding
is expected as of yet.

This front will be a high end gale force event for the eastern
gulf. Strongest winds will be north of Cape Spencer this morning,
then spread south past the Dixon Entrance by this afternoon as the
front moves east. Gusty conditions are expected over the inner
channels tonight with numerous small craft advisories in place as
well as a gale warning for Clarence Strait beginning this
afternoon. Strong winds are also expected along the northeast gulf
coast and the central outer coast today and tonight. Winds over
the gulf will diminish as the front finally pushes east over land
Thursday morning.

Model agreement was once again good through the short term.
Blended NAM, GFS, and ECMWF for updates to pressure. Used NAm as a
foundation for winds with high resolution NAM as a basis for wind
directions over the inner channels. PoP from NAMDNG and SREF. QPF
from NAM and RFC. Overall forecast confidence is average.

.LONG TERM.../Friday through Tuesday/ As of 10pm Tuesday...The
upper level jet that has been providing the warm weather slides SE
of the region by Friday morning. Meanwhile, a separate arm of the
jet stream will move into the Gulf of Alaska from the west,
however the upper level pattern quickly becomes amplified with a
ridge building over the eastern gulf and a trough over the
Aleutians/western gulf. This would cause a short period of NWLY
flow aloft over the panhandle Friday. This will help to break up
some of the lingering showers over the area. Temperatures at 850mb
cool enough for some of these showers to be a mix, but these pre-
frontal showers look to be light, so not expecting much in the
way of accumulation. Timing of the breaks will be critical for how
much the surface cools ahead of the next front. If the breaks
occur after sunset then things starting off as snow is more
likely.

The front will move across the gulf Friday afternoon as the upper
level ridge shifts to the east. Expect SE gale force winds with
this front over the outside waters. Flow aloft will increase out
of the SW causing temperatures to rise again as the front moves
inland Friday night into Saturday. Therefore expect a transition
to predominantly rain, especially as a stronger wave forms along
the front and intensifies the SWLY flow with moderate to heavy
rain Saturday. Expect a wind shift to the SW once the main part of
the front moves inland. The front then moves off the the SE
with colder air behind it, causing a transition to showers
Saturday night into Sunday.

Latest models have a weak low over the north-central gulf on
Monday that tracks to the S-SE through Tuesday. Meanwhile, the
upper level jet looks to finally reach up into the arctic and draw
down some colder air to the region next Tuesday. Both the upper
level and surface pattern would favor a shift to a northerly
outflow pattern which tends to be a dry one for us, although not
all models agree on this pattern change. With many differences
amongst models its too early to say this with much confidence 7
days out.

Overall preferred the GFS and Canadian models as they were in good
agreement through the extended period along with the NAM earlier
on.

 &&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind from Wednesday afternoon through late Wednesday
     night for AKZ023.
     Strong Wind from Wednesday afternoon through Wednesday evening
     for AKZ017.
MARINE...Gale Warning for PKZ041>043-051-052.
     Small Craft Advisory for PKZ012-013-021-022-031>036-053.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind from 3 PM AKST this afternoon through late tonight
     for AKZ023.
     Strong Wind from 3 PM AKST this afternoon through this evening
     for AKZ017.
MARINE...Gale Warning for PKZ036-041>043-051-052.
     Small Craft Advisory for PKZ013-021-022-031>035.
     Small Craft Advisory due to Seas for PKZ053.

&&

$$

Fritsch/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.