Small Craft Advisory 575, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
108 PM AKST Wed Nov 24 2021

.UPDATE...The earlier paradigm of warming Upper Lynn Canal sea
level locations with southerlies up through Lynn Canal has been
collapsing all morning as Southern Lynn Canal and Rocky Point has
recently flipped to northerly. This all the time would have
violated model indicated pressure gradients. But the feeling
previously was the momentum of winds from aloft would transfer to
the surface to allow this to happen. It did not this weekend, and
it increasingly looks doubtful now.

Therefore, we have preserved the northerlies and colder air
longer. With another wave lifting northward on Thursday, we feel
that while snow relaxes tonight, we think it will re-intensify
Thursday. Gradients and precipitation rates then begin relaxing
Thursday night as we have a more credible rise in temperatures and
the system pushes to the east into Canada. Therefore, we are
extending the winter storm warning through 9 PM Thursday night for
Haines and through 6 AM Friday for White Pass with lower amounts
near Skagway.

Finally, we lowered temperatures and kept Hyder all snow with
diabatic processes at work. Freezing levels continue to rise over
night, at least model indicated. So there will be a reckoning
between the diabatic processes and the overall warming of the
atmosphere overnight. For now, we added wetter snow with a mix
tonight and heavier snow this afternoon. Look for those changes
soon in the forecast.

&&

.PREV DISCUSSION......ISSUED AT ... 532 AM AKST WED NOV 24 2021

.SHORT TERM.../Wednesday through Wednesday night/...A gale-force
low associated with an atmospheric river to the south has moved
into the Gulf this morning with buoy 46083 reporting 37 kt winds
and gusts to 45 kt and reports of over a half an inch of rainfall
in Klawock and Ketchikan. Tonight a second low develops with a
second round of enhanced precipitation and winds.

A Winter Storm Warning for Skagway and Haines remains until 6 AM
Thursday. With breezy conditions picking up this afternoon in
Northern Lynn, expect lower snowfall rates and a warming trend in
temperatures that may change snow to a mix in Skagway this
evening, before transition back over to all snow. A Winter Weather
Advisory expires at noon today in Juneau, with 1 to 3 inches
falling overnight so far. A changeover from a mix to rain is
expected to occur late morning.

A High Wind Warning is in effect from 9 AM through 6 PM today for
Ketchikan, Prince of Wale, and surrounding areas with gusts up to
60 mph and areas reporting gusts to 50 mph early this morning.
Expected breezy conditions in those areas through Thursday. The
Strong wind headline remains this morning for Sitka and Port
Alexander, with gusts up to 45 mph and areas reporting gusts to
near 40 mph this morning. A second Strong wind headline for Port
Alexander is in effect from 3 PM today through 9 PM this evening
with gusts to around 45 mph.

Changes to the forecast included warming some areas including
Gustavus, which was reporting rainfall and temperatures of 39
degrees early this morning. Added in some details to the winds,
but limited changes to the overall forecast.

.LONG TERM.../Thursday through Sunday/ Upper level low over the AK
interior and extending down into the AK Gulf for the start of the
mid range will shift to the NE through the weekend with ridging
building over the gulf. A developing low now expected to move up
from the Pacific on Thursday. This will bring another round of
winds to the southern panhandle along with more precipitation to
the central and northern areas. As this low moves over the
panhandle and into the Yukon onshore flow generated by a low near
Prince William Sound will keep shower activity for most of the
region. Saturday into Sunday yet another low moves up from the N
Pacific but this has a more southerly track, which indicated drier
conditions for northern half of the panhandle with potential for
heavy precip for the south along with increased winds.

Timing of colder air moving in will be a determining factor in
precip type for Thursday evening. 850 mb temps dropping from -2 to
+2 C to -8 to -10 C within about 12 hours. This cold air
advection will shift rain back to snow showers. As of now think
the heaviest precip will occur before this warm up but do have
potential for an additional 2 to 5 inches of snow for Thursday
night into Friday. Places of concern for snow fall are Juneau,
Gustavus, Haines, and Yakutat. However as precip will be
convective in nature expect amounts to be highly variable.

For the Saturday into Sunday system moderate to heavy rain fall
with warm mid level air for the Southern panhandle. Higher IVT
from an atmospheric river just tagging our area but mainly hitting
southern British Columbia and NW CONUS. Offshore flow pattern
development getting the northern areas drier and colder with
increased northerly and outflow winds.

Low confidence on details for this weather pattern. Getting
enough shifts in pressure patterns from model run to run that
have significant impact on practical weather. Timing of
temperature shifts and thus precip type changes along with rates
result in uncertain snow totals. Used more GFS/ECMWF for the
Thursday night low. EFI has indicated impactful snow totals again,
but with showery nature and lower pops not confident so will keep
an eye on this. But overall be prepared for winter weather
through the end of the week with impacts to holiday travel and
events.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning until 6 PM AKST this evening for AKZ027-028.
     Strong Wind until 9 PM AKST this evening for AKZ023.
     Winter Storm Warning until 9 PM AKST Thursday for AKZ019.
     Winter Storm Warning until 6 AM AKST Friday for AKZ018.
MARINE...Gale Warning for PKZ031-034-036.
     Small Craft Advisory for PKZ022-033-035-041>043-051>053.

&&

JWA/KRT/PRB

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

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE JUNEAU AK
917 AM AKST WED NOV 24 2021

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

0300 AM     NON-TSTM WND GST HYDABURG                55.20N 132.82W
11/24/2021  M59 MPH          PRINCE OF WALES-HYDAK   AWOS

&&

CDC

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE JUNEAU AK
1051 AM AKST WED NOV 24 2021

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

1051 AM     NON-TSTM WND GST CRAIG                   55.48N 133.14W
11/24/2021  E60 MPH          PRINCE OF WALES-HYDAK   TRAINED SPOTTER

&&

CDC

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE JUNEAU AK
1052 AM AKST WED NOV 24 2021

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

1022 AM     SNOW             5 SSE HAINES            59.17N 135.39W
11/24/2021  M10.0 INCH       HAINES             AK   TRAINED SPOTTER

            MEASURED 10 INCHES OF NEW SNOW SINCE 4 PM
            AKST TUESDAY.

&&