Winter Weather Advisory 9, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
253 PM AKST Sat Jan 30 2021

.SHORT TERM.../Through Monday/ Multiple low pressure centers
continue to swirl around the Gulf of Alaska and panhandle today.
Satellite imagery shows at least 3 separate circulation centers
in the gulf with a fourth stronger one south of Haida Gwaii. These
lows have been sending waves of showers (mostly snow) over the
panhandle for the last 24 hours or so. Received snow reports have
been low with up to 3 inches received in some places overnight.

Not much has changed Through Sun night as the showers are still
expected to diminish through the next 12 hours. This is mainly due
to northerly outflow increasing tonight ahead of a new push of
cold air from the north. Winds in Lynn Canal are expected to reach
25 to 30 kt winds coming out of Taku Inlet and Cross Sound at the
same time.

More significant changes start showing up for Mon as a new low
forms in the northern gulf while outflow starts getting stronger.
Some more detail was added to the outflow winds compared to
previous forecasts, but overall wind changes were not that
substantial (Gale force winds still expected for Lynn Canal Mon)
Temperatures will also be cooling off again with some areas in the
northern half barely reaching 30 for highs on Mon.

The largest change in the forecast occurred at the end of the
short range Mon into Mon night as a low develops in the northern
gulf and slides SE. Current guidance has it sliding SE noticeably
faster then the previous forecast depicted, with the Nam and
Canadian faster then the ECMWF and GFS. However, Ensemble means
were supporting the slower solutions of the GFS and ECMWF, so
headed in that direction, but those were still a good 3 to 6 hours
faster then the previous forecast. Something to keep an eye on as
well, is that guidance is trying to form a convergence zone over
Kupreanof and Kuiu Island areas Mon into Mon night that could
result in some significant snow falls for those areas. Kept them
around advisory criteria for now, as confidence is low where
exactly it will set up, if it sets up at all, but snow totals
could range much higher or lower then currently depicted.

.LONG TERM.../Monday through Saturday night/ Extended forecast
period begins with a low pressure system encroaching on the region
from the west. A strong pressure gradient across the northern
panhandle will be the catalyst for some decent winds from Yakutat
to Skagway and areas south to the Icy Strait corridor and
Stephens Passage. Most areas should already be sufficiently cold
from offshore flow to see some snow from this system. While this
is not looking to be a particularly wet system, models are
beginning to come into agreement that there may be a bit more
moisture with this initial event than previously thought. While
highest snowfall totals still look to be set for northern areas,
there is growing indication that areas as far south as Ketchikan
could see an inch or two. For the time being, have switched gears
from the previous forecast and opted to leave the higher precip
amounts in for further scrutiny as the event draws nearer,
however, should offshore flow win out, this precip heavy forecast
may not come to fruition.

The next system that will impact the region moves in Tuesday
night into Wednesday. Still a decent amount of uncertainty exists
with this particular feature. While again, ambient conditions
should be cold enough across the region to initially support
snow, flow around this system will be coming in from the south.
The northern extent of this push of relatively warmer air will
again open up the forecast challenge of determining where the
elusive rain/snow line will be established. Combined with the
notion that any existing snow on the ground could contribute to
evaporative cooling makes this event too difficult to speculate on
particular impacts with any certainty at this time. What is known
is that this does look to have a tropical connection unlike it's
predecessor which could bring a decent amount of precip to the
region. After this system passes, another brief break in the
active weather pattern looks on tap before yet another system
potentially makes its way toward the region late week.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind until 9 PM AKST this evening for AKZ018.
MARINE...Small Craft Advisory for PKZ012-013-041>043-051-052.

&&

EAL/JDR

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