Area Forecast Discussion
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FXAK67 PAJK 142349

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
249 PM AKST Thu Dec 14 2017

.SHORT TERM.../Through Saturday night/ Rather active short range
forecast today. A strong front is currently moving through the
panhandle today that brought heavy rain (upwards of 1 to 2 inches
overnight) and gusty winds (30 to 35 mph) to many areas last
night and early this morning. The front will continue its eastward
trek into Canada this afternoon and evening with winds and precip
diminishing through that time.

Behind the front SW flow is the main pattern with shower activity
being the norm. However there is a an area of vorticity near 55N
150w that will rotate into the NE gulf by late tonight that will
enhance and possibly bring better organization to the showers
near it. There is also a weak pocket of cooler air aloft
associated with the vorticity max, so some heavy showers or even
some thunderstorms are not out of the question. A slight chance of
thunder was retained in that area for tonight

Focus then shifts to the next front approaching from the west for
Friday night into Saturday. Current model trends have the front
slightly slower then previous forecasts but still retaining at
least gale force winds as it crosses the gulf. Main forecast
change was the increasing of wind speeds in many areas of the
inner channels Fri night into Sat as the front moves in. Higher
resolution models were suggesting gale force winds at that time
for some areas like Stephens Passage and southern Lynn, but I
decided to limit those winds to around 30 kt for now to await
further runs.

This front also looks to be rather wet with a moisture plume
extending all the way down to the tropics. However, this front
does not appear to get hung up on the panhandle like last night`s
front did. Instead it appears to be a rapid mover from W to E so a
period of heavy rain is still likely for many areas but it should
not stick around long enough for flooding to become an issue. As
for ptype, sea level areas will still be too warm for snow,
however higher elevations of the Klondike Highway and maybe the
Haines Highway could get cold enough for snow so will need to be
watched as the front comes inland.

Short range models were in decent agreement. Namnest was used for
wind speed updates particularly in the inner channels Fri night
into Sat. Overall updates were handled with the Gfs and Nam though
most of those updates were minor.

.LONG TERM.../Saturday through Wednesday/ As of 10pm
Wednesday...The extended forecast starts off with a strong front
over the eastern gulf and widespread rain over the panhandle.
Models are now indicating a barrier jet and elsewhere along the
front to have storm force winds. Have increased wind speeds with
this package up to gale 35-45kt for now since models are still
showing some differences on when the peak timing would be. Winds
aloft will have shifted to the SW which will increase rainfall
rates to heavy at times again and keep temps on the warm side.
Therefore any place that had started off as a mix or snow will be
all rain by Saturday morning.

The low looks to move inland near PWS Saturday afternoon and
precip will transition to showers across the panhandle, although
remaining wet due to persistent onshore flow. Temperatures aloft
will start to cool at this point however, so do have places over
the northern inner channels with snow mixed in Saturday night and
Sunday. Not expecting much accumulation with this snow, potential
is there for a few inches, but warm surface temperatures will
likely cause the snow to melt on contact to start and
significantly limit accumulations.

Sunday night into Monday a new low center will be over the north-
central gulf. This will help to keep showers going (mostly rain
during the day and some mixing/snow at night) across the region.
But as the low tracks S-SE through Monday, winds will turn out of
the north and offshore, causing decreasing POPs and cloud cover
from north to south. Meanwhile the upper level jet will also have
turned out of the north and draw down colder air across the
region. Models have come in line with the shift to north winds on
Monday/Tuesday, but the GFS and Canadian keep that going Wednesday
while the ECMWF has it breaking down already with a shift back to
the SE. Think that it will persist a bit longer, so have
increased northerly winds through the inner channels through mid
next week. All signs point to this "cool down" back to normal
December temperatures to not last and things warming back up
above normal levels beyond the long range period.

Models were in better agreement on the overall pattern for this
package. Preferred the GFS for most updates as it was in line
with the forecast from yesterday and other models came into better
agreement with its solution. Forecast confidence is average, but
lower for accumulating snow.


.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind from 6 PM AKST this evening through late tonight for
MARINE...Gale Warning for PKZ051-052.
     Small Craft Advisory for PKZ011>013-021-022-031>036-041>043.
     Small Craft Advisory due to Seas for PKZ053.




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