Storm Warning 28, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
455 PM AKST Sun Nov 19 2023

.SHORT TERM...A very strong system advancing into the panhandle
will bring hurricane force winds to parts of the outer coastal
waters, high winds to parts of the panhandle, winter storm and
blizzard conditions to other parts of SE AK, and significant
amounts of rainfall to others through the next few days.

As of Monday evening, high pressure over the Yukon is working in
concert with a strong low advancing N towards the Gulf of AK to
strengthen the pressure gradient across the panhandle. This will
lead to a period of strong outflow winds, as an early season
northerly outflow event initiates Monday night. These outflow
winds will encourage significant cold air advection, as the
continental air mass normally located on on the Canadian side of
the coast mountains will successfully breach the mountain passes.
This will result in gale force winds and storm force winds across
the inner channels and outer coastal waters.

Concurrently, the scattered snow and rain showers across the
panhandle will to give way to more organized precipitation as the
low in the North Pacific advances into the Gulf. An occluding warm
front associated with the low will begin to move into the
southern panhandle Monday night. For the southern panhandle, this
will primarily be a rain and wind event. A High Wind Warning has
been issued for Prince of Wales Island, Annette Island, and
Ketchikan. Given the respectable amount of warm air advection and
fairly highly IVT values, opted to increase the total QPF for
these areas. Consequently, rainfall totals of between 2 to 3
inches near sea level with this system are anticipated across much
of the southern panhandle, and some river rises will occur.

As the system moves North, it will begin to overrun the
significantly cooler air from the outflow event which will
initiate an overrunning event. Although some snow accumulation is
possible for locations including Petersburg and Kake, anticipate
that the corresponding warm air advection with the system will
likely succeed in causing a rain snow changeover fairly early on,
and so have held these areas at a Winter Weather Advisory. it
should be noted that there is at least some chance Petersburg,
especially along the Mitkof Highway, could remain snow longer than
currently forecast, but at this time think this is the less likely
scenario.

As the system continues to advance North, the warm air advection
will increasingly struggle to push past the cold air outflow,
resulting in increasingly long periods of snowfall. Anticipate
that snow will begin through the early morning for places like
Angoon, before beginning during the morning proper for places like
Juneau, Hoonah, and Gustavus. While snow may initially be fairly
light, rates will rapidly increase and the greatest snowfall rates
for these locations will occur late Monday morning through Monday
afternoon. Gusty winds will also be present in these places, and
in Juneau, the oncoming system will collide directly with a
developing Taku Wind Event initiated by the northerly outflow.
This will result in significant reductions on visibility, and a
Blizzard has been issued for Juneau, alongside Winter Storm
Warnings across the Icy Strait Corridor. Snowfall rates will
diminish Monday night through Tuesday morning as the warm air
advection finally manages to reach the surface and overpower the
cold air advection. This will result in a changeover to a more
rain snow mix.

As the system continues to move North, it ultimately reaches the
northern panhandle. Anticipate that Haines, Skagway, and their
associated highways will see snow beginning later Monday morning
and see snowfall lasting through Tuesday morning. The Haines and
Klondike Highways will likely see the greatest snowfall totals
for the northern panhandle. In the wake of the system, anticipate
conditions improving for most locations through Tuesday, though
rain and snow showers will continue to move across the panhandle.

.LONG TERM.../Tuesday through Friday morning/ Mid range forecast
remains largely unchanged in the wake of the impactful wind and snow
event Monday. As mentioned in the short range, the storm force low
in the Gulf is still expected to move north and turn northwest on
Tuesday. Outflow winds will continue through Tuesday, and combined
with the storm force low in the Gulf, will result in continued gales
for most of the central and northern inside waters through Tuesday
morning. Otherwise winds throughout the inner channels will begin
to slacken Tuesday into Wednesday. As the low in the Gulf pushes
off to the west, rain and snow showers will continue across the
panhandle for the majority of the week with persistent southerly
onshore flow and a quasi stalled boundary. Overall looking to be
progressively relatively warmer from south to north for most of
the panhandle for the second half of the week as well.

&&

.AVIATION.../Until 00Z Tuesday/...CIG and VIS flight conditions
will deteriorate over the Panhandle and Inner Channels to between
MVFR and IFR and wind conditions will drastically deteriorate, as
well, as a storm to hurricane force frontal system moves up from
the south through the 24-hour TAF period. Those conditions will
progressively deteriorate from south to north out ahead and
along with the front starting around 06Z late this evening for
the southern Panhandle and starting around tomorrow morning for
the northern third of the Panhandle. Primarily snow will impact
the northern half to 2/3 of the Panhandle, and primarily rain will
impact the southern third to half of the Panhandle. As for winds,
the NE to SW pressure gradient will significantly tighten as the
front pushes northward starting late this evening and rapidly
increase the winds as we approach 00Z Tuesday. Copious amounts of
LLWS out of the NE for the northern third of the Panhandle and out
of the SE of the southern 2/3 of the Panhandle and strong SFC
winds will have spread over the entire Southeast Alaska region
associated with the aforementioned front by late tonight/early
Monday morning.

&&

.MARINE...Hurricane and storm force winds across the outer coastal
waters and the Gulf of Alaska, alongside storm force and gale
force winds for the inner channels. Wave heights will be
significantly elevated, reaching above 35 ft in the Gulf,
alongside fully developed seas for many of the inner channels.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind from midnight AKST tonight through Monday morning
     for AKZ318.
     Winter Storm Warning from 9 AM Monday to 3 PM AKST Tuesday for
     AKZ318-319.
     Winter Storm Warning from 3 AM Monday to 3 AM AKST Tuesday for
     AKZ320>322.
     Winter Storm Warning from 3 AM to 9 PM AKST Monday for AKZ324.
     Blizzard Warning from 6 AM Monday to 6 AM AKST Tuesday for
     AKZ325.
     Winter Weather Advisory from midnight tonight to noon AKST
     Monday for AKZ326-327.
     High Wind Warning from 6 AM Monday to midnight AKST Monday night
     for AKZ328-330-332.
MARINE...Hurricane Force Wind Warning for PKZ644-663-664.
     Storm Warning for PKZ012-022-053-642-643-651-661-662-671-672.
     Gale Warning for PKZ011-013-021-031-032-035-036-641.
     Small Craft Advisory for PKZ033-034-652.

&&

SHORT TERM...GFS
LONG TERM....STJ
AVIATION...JLC

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