Winter Weather Advisory 13, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
256 PM AKST Wed Feb 17 2021

SHORT TERM.../Wednesday Afternoon Through Friday/

The story for today was the front that continues to impact the
northern gulf coast. Good lift in the dendritic growth zone,
coupled with a persistent east wind, kept enough cold air in
place in Yakutat to efficiently produce snow. Seven inches
were reported as of 1pm this afternoon with snow still falling. A
change to rain is still expected this evening, but the exact
timing of the change remains uncertain. A Winter Storm Warning
remains in effect until 6pm. Elsewhere, light snow was observed
across the northern half of the panhandle with mostly cloudy skies
across the south. Winds were slow to respond in the inner
channels but are finally turning to the south and increasing in
Lynn Canal and Skagway, bringing some warmer air north for this
evening. On to the next storm ...

IR satellite imagery is currently showing high clouds from the
next approaching system already encroaching on Prince of Wales
Island. The storm force low (~965mb) will be entering the eastern
gulf from the south on Thursday. Today's forecast made slight
modifications to the track, taking it north into the central gulf
before turning northeast and coming onshore south of Cross Sound
Friday afternoon. The bulk of the work today focused on
pinpointing the high wind potential. This afternoon's forecast
package will include a High Wind Warning for the Ketchikan area,
Annette Island, and Prince of Wales Island and a High Wind Watch
for Sitka and vicinity. Gusts to 60mph will be more certain for
the southern Panhandle. The low will be weakening slightly as it
makes its trip north, making high wind criteria less certain for
Sitka but this will be monitored. Easterly flow ahead of this next
storm will dry the panhandle out a bit tonight with precipitation
starting in earnest on Thursday. Strong warm air advection is
present which will warm many areas up above freezing. The 40
degree mark might be reached as far north as Yakutat, and Gustavus
Thursday afternoon. As a result, the precipitation will mostly be
in the form of rain, with the exception of northern Lynn Canal
where a northerly pressure gradient will cause Haines and Skagway
to start as snow before changing to rain. The Haines and Skagway
areas will need to be watched for potentially moderate amounts of
snow accumulation before the changeover to rain. With continued
southerly flow for most areas into Thu night rain will continue to
be the main precipitation type into Fri.

LONG TERM.../Friday through Wednesday as of 10 pm Tuesday/ Little
change in thinking for this forecast period. Friday, the panhandle
will be under the influence of a low pressure system off the
central coast. Guidance agreement has further aligned with one
another placing the low just southwest of Cape Spencer by early
Friday morning. The low then looks to shift east into the
panhandle through the Icy Strait corridor before dissolving into a
shortwave. Precipitation chances remain elevated through the
weekend as onshore flow funnels moisture into the panhandle.

A stronger low develops along the Aleutian Islands Saturday.
Ample moisture support also looks favorable as it transports
moisture from the Pacific into the Gulf. By Saturday afternoon QPF
values increase as the associated front lifts into the panhandle
through Sunday. The parent low looks to remain situated in the
northern Gulf before shifting south along the coast through early
next week.

During the long term forecast one tends to look for
pattern changes, for example dry vs wet patterns, as more detailed
pieces of the forecast are harder to nail down. For this forecast
period, one could say an active wet pattern looks favorable. For
the fair-weather lovers out there, don't loose hope just yet. By
Wednesday, new guidance suggest a surface ridge to build through
the panhandle for about 24 hrs providing brief relief before yet
another low impacts the panhandle late week.

As for temperatures, an overall warming trend can be expected.
Beginning Friday, 850 mb temps steadily rise as each passing low
transports midlevel warm/moist air into the panhandle. Daytime
highs in the upper 30s to lower 40s and overnight lows in the mid
to upper 30s are expected through the weekend. Forecast challenges
will be centered around precipitation type as marginal
temperatures will support both snow and rain depending on frontal
passage and diurnal tendencies.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind from late tonight through Thursday afternoon for
     AKZ026.
     High Wind Warning from 3 AM to noon AKST Thursday for AKZ027-028.
     Strong Wind Thursday afternoon for AKZ027-028.
     Strong Wind Thursday afternoon for AKZ023-025.
     Strong Wind from Thursday morning through Thursday afternoon for
     AKZ022.
     High Wind Watch from Thursday morning through Thursday afternoon
     for AKZ023.
     Winter Storm Warning until 6 PM AKST this evening for AKZ017.
MARINE...Storm Warning for PKZ041-042.
     Gale Warning for PKZ033>036-043-051.
     Small Craft Advisory for PKZ012-013-021-022-031-032-052-053.

&&

BFL/CC

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