Wind Chill Advisory 2, NWS Juneau, AK

Southeast Alaska Forecast Discussion...CORRECTED
National Weather Service Juneau AK
1123 PM AKST Mon Jan 7 2019

.SHORT TERM.../Through Wednesday night/ Some light to moderate
snow is starting to spread across most of the panhandle today as a
weak disturbance in the NE gulf pushes some warmer moister air
over the cold arctic air in the inner channels. Winter weather
advisories remain up for many areas of the central and southern
panhandle through the night for 2 to 6 inches. Exact totals will
vary due to several factors. First, qpf is rather low for this
system (most areas should see around 2 tenths of an inch or less
of liquid equivalent), however with the cold air in the inner
channels, snow ratios will be on the order of 20 to 1.
Additionally, satellite imagery shows that there is some embedded
convection that could lead to locally higher snow totals
especially if these cells start training over a location.

By Tuesday morning, the upper trough that was sustaining the snow
will have moved into Canada and northwest flow moves in behind
it. Precip and clouds should be clearing out through the day. Also
the surface high in Canada will be gradually strengthening so the
already present outflow will gradually increase.

Things start to rapidly change Tuesday night. An approaching low
from the S will start to rapidly increase the pressure gradient
along the coast range. Outflow will start to increase significantly
with winds rising to gale and possibly even storm force in Lynn
Canal and Taku Inlet by Wednesday. Downtown Juneau and Douglas are
under the gun for high wind gusts again as well. The critical
level and inversion are there and the cross barrier flow is a bit
stronger then the last event so decided to issue a high wind watch
for late Tue night into Wed evening. Meanwhile a frontal band
will be spreading N dropping snow as it goes before warm air
advection with it starts changing things over to rain for the
south. Expect a few inches of snow for southern areas on Wed
before the change over happens though.

Most changes focused on local effects. Mainly used Nam and Gfs.

.LONG TERM.../Wednesday through Sunday night as of 10 pm Sunday
evening/ Outflow conditions persist at the beginning of this long
range forecast period with northerly/easterly gales over most of
the inner channels and a strong potential for storm force winds
over Lynn Canal. Continued colder than normal temperatures will
accompany these winds. At the same time over the southern
panhandle, a front and significantly warmer temperatures will
begin moving north. Precip type at first will be snow with the
leading edge of the front as it moves north, but low level warm
air advection will result in a transition from snow to rain as the
front moves north. This first of multiple fronts will stall about
half way up the panhandle and then by over run by a second front
on Friday. This second one will contain more precipitation, more
warm low level air, and make more progress to the north, pushing
the rain/snow line north as it goes. A third front will approach
Southeast Alaska from the southwest on Saturday afternoon. Long
range guidance suggests that there will be at least two more out
to the end of the model run.

By the end of the upcoming week, the rain/snow line near sea level
will likely be north of the Icy Strait corridor as a significantly
warmer low level airmass scours out the very frigid air now in
place at the surface. As a result, only the far northern inner
channels will possibly remain in snow through next weekend.

Used GFS for updates to pressure and wind Wednesday through
Wednesday night. Minimal changes to pressure and wind thereafter
as the current WPC forecast was close to the existing forecast.
Blended GFS and SREF PoP for the first front with the effect of
slowing down northerly progress. Retained existing PoP grids later
on as a middle ground between faster and slower models with the
second and third fronts. Temperatures were warmed up using ECMWF,
GFS, and the NBM with the potential for more adjustments upward
in subsequent shifts. Overall forecast confidence is average.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Weather Advisory until 5 AM AKST Tuesday for AKZ025-026-
     028.
     High Wind Watch from late Tuesday night through Wednesday
     evening for AKZ025.
     Winter Weather Advisory until 9 PM AKST this evening for AKZ022.
     Winter Weather Advisory until midnight AKST tonight for AKZ020-
     021.
MARINE...Gale Warning for PKZ022.
     Small Craft Advisory for PKZ012-013-021-031-042-043-051.

&&

EAL/Fritsch

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