Small Craft Advisory 39, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
345 PM AKST Sat Jan 13 2018

.SHORT TERM...During the transition from snow to rain today, there
was a bit of a lag with the cold air at the surface and warmer air
aloft resulting in freezing rain over many areas around the
Panhandle between Sumner Strait and the Icy Strait corridor.
Freezing will end from south to north and will move up to Haines,
especially along the highway by this evening.

The atmospheric river that is approaching and is showing no signs
of letting up. It will affect the entire Panhandle but Yakutat
will take the brunt of the force. Heaviest rainfall will begin
late this afternoon/early evening with 3 hourly amounts of 1/3 of
an inch or more north of Icy Strait, extending inland to Juneau.
Yakutat could see up to half an inch every 3 hours starting this
evening through early Sunday morning. Rainfall rates will be on
the decline through the day Sunday as the heaviest rainfall shifts
to the west of Yakutat. Wet conditions will continue for the
northern half of the Panhandle into Monday.

The incoming front is also bringing strong winds to the outer
coastal areas, this afternoon into Sunday. Storm force winds are
blowing in Cross Sound, diminishing to Gale force this evening.
Strong winds will work their way inland into Juneau and Ketchikan
late this evening.

NAM was used for updating along with manual forecaster
adjustments. Overall, the forecast is staying on script with just
a few adjustments for timing as the front is moving slightly
slower and the temperatures are warming slower. The temperature
delay is a duo effect of a stubborn cold layer at the surface and
winds that failed to develop on time. Even with these changes,
the end of the story will end the same with the snow being washed
away and mild weather encompassing SE Alaska to start out the new
work week.

.LONG TERM.../Monday through Friday/ The early part of the long-
term period will start off as warm and wet, before transitioning
to a warmer, drier pattern during mid-week. As a strong
atmospheric river wraps up, there is consensus for a low tracking
northward through the Gulf late Sunday into Monday. This
undercutting low will lead to offshore flow and help to dry out
the panhandle.

Additionally, most of the long-term focus yesterday evening was
shifted to the short-term due to an active frontal passage and
ongoing snow/ precipitation issues. As a result, no major changes
were made and models still give a general idea of this next
system.

The weakening of the ridge over western Canada during the early
part of the period will allow for temperatures to remain above
average and decrease through the extended period as intermittent
amounts of shortwave energy are injected into the overall pattern.
This will bring persistent rounds of heavy precipitation across
the panhandle and gusty winds later into the week. Winds over the
inner channels will remain relatively light during the early part
of the period due to the parallel pressure gradient.

POP and QPF were blended with the NAM and EC to better show the
clearing precipitation to the west of Yakutat. Temperatures were
increased Sunday into Monday to reflect the occurrence of warm air
advection, but minimal adjustments throughout the week and
remain within guidance.

Model spread increases gradually later on in the period, but with
some evidence of another low pressure system tracking from the
eastern Aleutians through the Gulf into Thursday. However, confidence
remains moderate for the timing of the next low into Monday.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind through late tonight for AKZ027.
     Winter Weather Advisory until 4 PM AKST this afternoon for
     AKZ025.
     Strong Wind through late tonight for AKZ023.
     Winter Weather Advisory until midnight AKST tonight for AKZ029.
     Winter Weather Advisory until 5 AM AKST Sunday for AKZ019.
     Winter Storm Warning from 4 PM this afternoon to 5 AM AKST
     Sunday for AKZ018.
MARINE...Storm Warning for PKZ052.
     Gale Warning for PKZ022-036-041>043-051.
     Small Craft Advisory for PKZ012-013-021-031>035.
     Small Craft Advisory due to Seas for PKZ053.

&&

KV/SS

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