Winter Storm in Alaska, February 18 to 19, 2019

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
309 PM AKST Sun Feb 17 2019

.SHORT TERM...The current satellite imagery show a broad area of
clouds over the Gulf of Alaska which are moving over the forecast
area as the upper level ridge that has provided some nice sunny
days drifts east. There will be 2 impactful weather fronts to
move over the forecast area the next few days. The first one will
be tonight, which will be quick and weakening as it moves over
the area. The second will move over the panhandle through Monday
night and will be much stronger with more moisture available along
with better mid level dynamics for lift. There were not many changes
to any winter weather product with the exception to lowering some
snow amounts in places. Overall there is about average forecaster
confidence.

There is a surface front under the cloud cover and is affecting
the Yakutat area this afternoon with some light snowfall and or
mist due to some drying in the mid levels. The profile will
moisten through this evening and moderate snow will begin to fall
with about 4 to 5 inches by the early morning. There maybe some
a break in the precipitation in the late morning but as the next
front moves over the northern gulf the Yakutat area will see snow
and rain. Amounts will be tricky as there is caa but with being
so close to the ocean they may remain a mix.

For the rest of the area, the first front will bring some snow to
the coastal and north central inner channels with about 3 to 5
inches by mid Monday morning. There is some concern that snow
ratio values will lower due to mid level warning and not produce good
snow development. There will be some minor snow accumulations
over the the rest of the northern half. The snowfall rates will
relax during the day on Monday as the first front exits the area
but that will not last long with snow rates increasing in the late
afternoon into the evening hours. There were some minor
adjustment done to snow amounts but over all snow amounts may
range from 4 to 8 Monday night. More winter weather products will
be needed for the south central areas as there is indication that
may be advisory snow amounts.

Wind wise...the first front is producing gale force winds over the
northern gulf with small crafts developing over the eastern gulf
tonight. There is not much wind over the inner channels now but as
the first front moves over the area it will sharpen up the
surface ridge and increase the south winds to range from 15 to 30
kt. The winds will relax between the systems but then increase
again to those levels Monday night. As the low drifts southeast
through Wednesday the northerly outflow winds will increase along
with a drying conditions.

.LONG TERM.../Tuesday through Sunday as of 10 pm Saturday/
Longwave pattern will generally keep ridging over the NEPAC with
troffing over the N-central PAC and the Bering Sea. However, there
will be several shortwaves, some on the strong side, that will
flatten the ridge as they move through during the week into next
weekend. Model differences with the shortwaves have increased in
the past 24 hrs worth of model runs, so decided to make little
change to most forecast parameters.

A stronger shortwave and occluded front will be over the inner
channels early Tue morning, and heading SE. System will bring in
some warmer air, so the rain/snow line appears to move inland some.
Still some differences in how much lower level cold air hangs on
over the more eastern and northern areas, so limited any
transition to a mix for most of those spots during Tue. Some of
the 00z models are a little cooler around the Juneau area Tue
(based on 1000-850 thickness) than previous runs, so later shifts
may need to lower temps a bit (and possibly maintain snow longer).

After that, still looks like a break in the precip starting Tue
night and continuing into Wed. Models have increased their spread
on system moving in for late week, and there has been little run
to run consistency either. So, sticking with current forecast
seemed to be the best idea for late week. The differences only get
larger over the weekend, ranging from a cold/dry scenario in the
latest GFS to a warmer and wetter scenario in the Canadian model.
Overall, forecast confidence is average through midweek, then
below average for late week into the weekend.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Storm Warning from midnight tonight to 9 AM AKST Tuesday
     for AKZ025.
     Winter Weather Advisory from 9 PM this evening to 9 AM AKST
     Monday for AKZ020-022.
     Winter Weather Advisory until 5 AM AKST Monday for AKZ017.
MARINE...Gale Warning for PKZ051-052.
     Small Craft Advisory for PKZ012-013-021-022-042-043.
     Small Craft Advisory due to Seas for PKZ041-053.

&&

ABJ/RWT

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