Area Forecast Discussion
Issued by NWS
FXAK67 PAJK 051444
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
544 AM AKST Mon Dec 5 2016
.SHORT TERM...Cold air has infiltrated the panhandle over the last
24 hours. Temperatures have dropped into the teens and 20s for
most areas overnight with some single digit readings in the
extreme northern panhandle. Outflow winds have also been active.
Lynn Canal and Stephens Passage have been blowing gale force most
of the night with 25 to 30 kt winds for the rest of the northern
inner channels. The combo of wind and cold temperatures have
caused wind chills to drop to around minus 30 on the Klondike
Highway near White Pass prompting a wind chill advisory for that
Outflow winds and cold temperatures will be the main forecast
concern for the next 24 hours. Cold air will continue to flow over
the mountain passes and with mostly clear skies tonight
temperatures will drop into the 20s and teens again with single
digit temps possible over several areas in the northern inner
channels. Outflow winds will also continue but will be on a
decreasing trend. Cold air outflow will keep the winds somewhat
gusty but pressure gradient will become less of a factor due to
the southerly retreat of the low near Haida Gwaii. By late tonight
many of the small craft advisories up for the inner channels will
have diminished and the gales in Lynn Canal will have lessened to
around 25 to 30 kt.
As for the wind chill advisory for White Pass. Higher winds today
will keep the wind chill around -30. For tonight, winds will
lessen but air temperatures will have lowered enough to render
that decrease in wind ineffective at warming wind chills. So no
change to the wind chill advisory duration at this time.
Otherwise weather is mostly quiet. There is some snow moving into
the central gulf and northern gulf coast tonight from a weak low
entering the western gulf. However, precip amounts are expected
to be light with only around an inch of snow accumulation
expected. Precip is not expected to start up until after midnight
Used mainly some NAM for updates with most changes related to
local wind effects.
.LONG TERM...Low pressure system that moved into the western gulf
will become nearly stationary through mid week before pulling back
to the west and south. Frontal boundary associated with the gulf
low moves along the coastal waters with areas of gale force winds
developing. Uncertainty with a short wave extending from the
parent low over the central panhandle and its exact path. Another
surface low potentially moves near Haida Gwaii over the weekend.
Arctic high over the Yukon starts to expand south covering both
the Yukon and portions of British Columbia.
Trended towards raising pops with the advancing gulf low. Higher
confidence that Yakutat will receive snow starting Tuesday into
Tuesday night. Earlier models runs limited eastward expanse but
now more indications that snow will move as far east as Juneau.
SREF/ECMWF kept precip to the west, while GFS/GEM have categorical
pop over most of the central panhandle. Decided to use SREF as a
base but add at least 50% pop for locations covered by GFS/GEM.
While confidence is starting to rise for higher pops and as there
will be cold air in place and elevated instability/ moisture of
over running snow event, current QPF values producing snow
amounts not much more than 2 to 4 inches. For some locations,
such as Juneau, QPF is at the upper end of the model spectrum
spread so even going with a higher bias not getting a significant
Canadian arctic air still in place panhandle temps will remain
low. May have slightly higher overnight temps due to increased
cloud cover. Northerly winds will vary as the pressure gradient
shifts to more east west as the gulf low moves in, then shifts
back to north-south later in the week with increasing speeds.
Not much change to press field for Tue but updated with a GFS/EC
blend starting Wed which put the low center further north. As
stated above used mostly SREF for pop with a mix of GEM/GFS. Model
are falling more in line with the synoptic pattern but still large
spread at meso scale, thus have low confidence for the mid range.
PUBLIC...Strong Wind until 9 AM AKST this morning for AKZ025.
Wind Chill Advisory until 9 AM AKST Tuesday for AKZ018.
MARINE...Gale Warning for PKZ012-013-031.
Small Craft Advisory for PKZ011-021-022-032-034-051-052.
Small Craft Advisory due to Seas for PKZ041>043.
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