Gale Warning 45, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
234 PM AKST Wed Jan 29 2020

.SHORT TERM...Potentially damaging winds and heavy snowfall likely
over parts of SE AK tonight into Thursday.

Strong front that brought high winds and heavy precipitation to SE
AK last night and this morning now passing northward into BC and
the Yukon as of early this afternoon. Winds have gusted as high as
60 to 70 mph in Haines/Skagway late this morning and as high as 55
mph in Juneau where some minor tree damage has been reported. Rain
has been the predominate ptype for sea level Haines but as much
as 22 inches has been reported near Haines Customs and based on
cameras, near blizzard conditions are being experienced along the
Klondike Highway.

Attention now turns to the next developing storm system to the
SW. GOES 17 imagery this afternoon shows a deep upper trough
digging into the western Gulf behind the current system. Cold air
is pouring southward into the Gulf underneath this trough and
this air will be advected eastward and across the northern part of
the Panhandle tonight. To the south, a vigorous PV max embedded
within a 180kt jet streak will interact with the deep upper trough
over the Gulf late tonight. This disturbance will amplify as it
becomes favorably superimposed on the east side of the deep PV
anomaly associated with the upper trough to the west. The result
will be a rapidly intensifying surface cyclone which will be
tracking from the SE Gulf into and across the central Panhandle
Thursday morning. Most guidance deepens the low to sub-970mb as it
makes landfall somewhere along the eastern Gulf coast Thursday
morning. Low level wind fields will be nothing less than
impressive, with a 70-80kt low level jet preceding the front. Even
more impactful will be the developing bent-back warm front which
will affect areas from Sitka to Angoon and potentially Juneau
Thursday morning. Low level wind fields within the bent-back front
look to be 60 to 70kts. This will likely lead to a swath of
W'ly to SW'ly winds of 40 to 50kt with higher gusts approaching
60kt over the inside waters from Chatham Strait northward. Gusts
over land areas will approach 70 mph for a short time on Thursday
morning just south of the track of the low. Pressure rises
approaching 4mb/hr behind the system will lead to an isallobaric
wind up Lynn Canal Thursday afternoon will lead to max gale
conditions all along the Canal and into Haines and Skagway by late
Thursday afternoon.

Prior to the rapid wind shift, strong low to mid level
frontogenesis and moisture transport will lead to tremendous
precipitation rates. With snow levels hovering around 1000 ft late
tonight and gradients initially becoming light and northerly,
think precipitation will change to heavy snow from Juneau, Hoonah,
and Gustavus northward. Given the shear amount of dynamic forcing
for ascent, snowfall rates of 2 inches per hour are likely within
the trowel region of the low through the morning hours Thursday.
Will be issuing a Winter Storm Warning to cover the impacts from
both heavy snow and high winds from Juneau northward.

Still some track and timing differences in the models on the track
of the surface low. The GFS and EC have been the most consistent
in the track currently depicted in our forecast so decided to hold
steady with a track from just north of Sitka into the Juneau area.

Residents of SE AK should be prepared for rapidly changing weather
conditions and take precautions to protect property against damage
from the winds.

.LONG TERM.../Friday through Tuesday/ As of 10pm Tuesday. Cooling
trend expected for the beginning of the extended forecast with
predominately snow showers for the p-type. Low pressure over the
NW gulf will keep the region under SW onshore flow and cold air
advection (CAA) will enhance ocean effect showers Friday into
Saturday. There is potential for a couple inches of snow out of
these showers for most of the panhandle.

The low center will gradually track SE along the outer coast
through Saturday night. This will cause the main precip potential
to shift southward while increasing offshore flow over the
northern inner channels decreases pop there. By Sunday morning the
northerly winds through the inner channels will have set in along
with skies becoming partly cloudy or better. Sunday daytime is our
best chance for a dry, fair weather day in the extended, but also
likely the coldest day of the week.

Sunday night into Monday a new weather system looks to track
across the gulf from the west. This brings with it a warmer
airmass, so expect snow initially, changing to rain Monday night
into Tuesday.

Models are in good agreement through the long term period,
allowing for above average confidence in wet/dry periods and a
cooling trend through the weekend followed by a warming trend for
the start of next week.

&&

.AVIATION...Widespread IFR to LIFR conditions will occur Thursday
morning as heavy snow breaks out for PAGS, PAJN, and points north.
Additionally, dangerous low level wind shear conditions will be
present with SW winds aloft behind the low as high as 60 to 70kt
affecting central and northern terminals between 18Z Thursday and
00Z Friday.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...High Wind Watch from Thursday morning through Thursday afternoon
     for AKZ021-022-024>026.
     High Wind Watch from late tonight through Thursday morning for
     AKZ027-028.
     Winter Weather Advisory from midnight tonight to noon AKST
     Thursday for AKZ025.
     Strong Wind until 6 PM AKST this evening for AKZ025.
     Strong Wind until 3 PM AKST this afternoon for AKZ022-023.
     High Wind Warning from 3 AM to 6 PM AKST Thursday for AKZ023.
     Winter Storm Watch from midnight AKST tonight through Thursday
     morning for AKZ020-021.
     Strong Wind until midnight AKST tonight for AKZ019.
     Winter Storm Warning until 6 PM AKST this evening for AKZ018.
MARINE...Storm Warning for PKZ041.
     Gale Warning for PKZ012-013-022-031-032-034>036-042-043-051-052.
     Small Craft Advisory for PKZ011-021-033-053.

&&

DEL/Ferrin

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

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE JUNEAU AK
1121 AM AKST WED JAN 29 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0342 PM     NON-TSTM WND GST SE KETCHIKAN            55.35N 131.68W
01/28/2020  M61.00 MPH                          AK   C-MAN STATION

0854 PM     NON-TSTM WND GST THORNE BAY              55.69N 132.52W
01/28/2020  M69.00 MPH                          AK   MESONET

0900 PM     NON-TSTM WND DMG THORNE BAY              55.69N 132.52W
01/28/2020                                      AK   CO-OP OBSERVER

            TREES DOWN ON HOUSES, SCHOOL DISTRICT DOCK RAMP
            DISCONNECTED. TREE BRANCHES NEAR 1 INCH OR BIGGER ON
            HOUSES AND GROUND.

0912 PM     NON-TSTM WND GST SE KETCHIKAN            55.35N 131.68W
01/28/2020  M79.00 MPH                          AK   C-MAN STATION

1110 PM     NON-TSTM WND GST 6 ENE COFFMAN COVE      56.06N 132.70W
01/28/2020  M77.00 MPH       PKZ036             AK   C-MAN STATION

1113 PM     NON-TSTM WND GST 2 ESE KETCHIKAN         55.34N 131.64W
01/28/2020  M60.00 MPH                          AK   C-MAN STATION

1122 PM     NON-TSTM WND GST 5 NNW SITKA             57.12N 135.39W
01/28/2020  M60.00 MPH                          AK   C-MAN STATION

1153 PM     NON-TSTM WND GST 2 ESE KETCHIKAN         55.34N 131.64W
01/28/2020  M61.00 MPH                          AK   C-MAN STATION

1154 PM     NON-TSTM WND GST THORNE BAY              55.69N 132.52W
01/28/2020  M67.00 MPH                          AK   MESONET

&&

CC