Gale Warning 41, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
235 PM AKST Tue Jan 28 2020

.SHORT TERM...Two powerful winter storms to affect SE AK over the
next 48 hours. Potential for damaging winds and heavy snow along
with high seas will continue through Thursday.

The first major storm is seen clearly on GOES 17 imagery this
afternoon with a 955mb center analyzed near 50N 150W. ASCAT passes
reveal a broad swath of 40 to 45 kt winds along a rapidly
occluding front now pushing northward into the southern Gulf as
well as several uncontaminated 50kt barbs in the bent-back
warm front south of the low. The occluded front will continue
towards the Panhandle tonight and cross the Panhandle towards
morning. The strong low will weaken slightly as it tracks north
and northeast ending up just along 140W in the northern gulf by
mid morning Wednesday. Deep upper trough to the west will interact
with this system and pull it back to the west as very cold arctic
air pours out into the western Gulf in the wake of the surface
low. Low level wind fields will be quite strong ahead of the front
and the surface wave, with as much as 80-90kts noted at 925 and
850mb. Surface pressure gradients will favor very strong winds
along the Gulf coast and over the central and southern inside
waters tonight, spreading northward during Wednesday. Coastal
convergence will lead to storm force winds over the eastern Gulf
with storm conditions over Clarence Strait and gales elsewhere
over the inside waters through Wednesday. Given the amount of low
level momentum and favorable surface gradient orientation, think
wind gusts to 60 mph are still likely along the eastern Gulf Coast
and in channeled areas of the southern Panhandle.

To the north, the airmass that had advected in from the Gulf
behind the last system has been notably warmer than previously
thought, likely due to the long passage over the warmer Gulf
waters. Thus temperatures in the boundary layer are warmer than
expected this time yesterday. While the surface gradient over
upper Lynn Canal will turn northerly this evening, there is some
doubt as to how much cold air will be able to be maintained near
the surface. Still, very strong moisture transport of 50 to 60 kts
over a relatively stable layer near the surface should result in
heavy precipitation rates and allow the column to cool to near
freezing over Haines and Skagway later this evening. Think a rapid
wind shift to the S will occur late Wednesday morning or afternoon
though and with all this in mind, trimmed back snowfall totals in
the warning area. Highest amounts are expected over the higher
elevations of the Klondike Highway where near blizzard conditions
are possible Wednesday as the wind shifts to the S.

Now for storm number two! Very cold air will pour into the Gulf
behind storm number one on Wednesday. This will effectively deepen
and broaden troughing over the Gulf into Wednesday night. A
vigorous PV max and attendant 180kt jet streak will ride this
baroclinic zone towards the central/southern Panhandle late
Wednesday night. The result of this interaction will be a rapidly
developing surface cyclone, which given the amount of forcing will
be driven directly across the Panhandle Thursday morning. This
will be a very fast-moving and dynamic system with the potential
for widespread wind damage along and south of the track. Just to
the north of the track of the low, a 3 to 6 hr period of very
heavy snowfall is likely, followed by a rapid wind shift to a
westerly or southerly direction. Sting jet developing on the
backside of the storm will lead to the potential for very strong
westerly winds in places that typically do not experience strong
winds from that direction. The good news is that at this time, the
low looks to make landfall during an ebb tide so no coastal
flooding is anticipated at this time. Models have come into a
little better agreement on the track of the system today so went
with a middle of the road approach with the storm making landfall
over Baranof Island and a track just south of the Juneau area
Thursday morning. A shift of a few miles in either direction would
make a huge difference in the type of weather any one location
receives so held back on any wind or winter headlines at this
time, especially given the on-going weather from storm number one.
It should be noted that residents of SE Alaska should be prepared
for rapidly changing weather conditions late Wednesday night and
Thursday morning and stay tuned for updates on this potentially
dangerous storm.

.LONG TERM.../Thursday through Monday/...A significant storm
system is possible to impact the southern or central panhandle
Thursday morning. Models are in poor agreement with placement and
timing of the low. Upper trof will continue over the N gulf. Upper
shortwave will lift into the SE gulf early Thursday and across the
panhandle. The low will likely rapidly develop as it moves into
the SE gulf. Currently using a NAM/EC consensus on a low moving
over the southern panhandle with gale force winds, but it is
possible for much stronger winds. Again, confidence is low
regarding exactly where the strongest winds will occur.

Precipitation will spread N across the panhandle as the system
moves over the area Thursday. Snow will be possible along the Icy
Strait corridor northward, especially if the winds turn north long
enough for cold air to move in. Current amounts are low confidence
as well. Low level cold air will continue to wrap around a low in
the N gulf Friday and Saturday. Snow showers will be the most
likely form of precipitation late week. The low will then slide SE
Sunday as a weak ridge moves across the gulf and the panhandle.
Still think there could be a brief break in precip Sunday, before
the next system pushes across the region Monday.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...High Wind Warning from 6 PM this evening to 3 AM AKST Wednesday
     for AKZ023-026>028.
     Strong Wind Wednesday morning for AKZ026>028.
     Strong Wind from late tonight through Wednesday afternoon for
     AKZ025.
     Strong Wind from Wednesday morning through Wednesday afternoon
     for AKZ023.
     Strong Wind from late tonight through Wednesday afternoon for
     AKZ021.
     Strong Wind from Wednesday morning through Wednesday afternoon
     for AKZ029.
     Winter Storm Warning from 6 PM this evening to 6 PM AKST
     Wednesday for AKZ018-019.
     Winter Weather Advisory until 6 PM AKST this evening for AKZ017.
MARINE...Storm Warning for PKZ036-041>043-051-052.
     Gale Warning for PKZ012-013-022-031>035.
     Small Craft Advisory for PKZ021-053.

&&

DEL/DDH

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