Gale Warning 123, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
341 PM AKDT Wed Mar 29 2017

.SHORT TERM /Wednesday night through Friday/...Troughs of low
pressure will continue to move across the area tonight into
Thursday. These will keep the showers going for majority of the
panhandle. Models have picked up on one of these troughs and are
in agreement that it will be of more impact than we were seeing
yesterday. The trough will approach the Sitka area overnight and
increase winds over the outside waters some, along with a period
of moderate showers. This trough will keep isolated to scattered
showers going, namely over the northern half of the panhandle for
most of the day Thursday. 850mb temps cool some behind the trough,
this along with rates could incite some snow to mix in early
Thursday morning, but little to no accumulation is expected.

A gale force front will move across the gulf on Thursday with precip
reaching the outer coast in the early evening then spreading inland
through the night. This looks to be a warm system with almost all
areas getting rain. Southerly winds area wide will help with this
idea. The outer coast could see wind gusts of around 40mph with
the front while the inside areas could have gusts of 25-35mph.
Rainfall rates will be moderate to heavy at times. For locations
that have snowpack blocking drainage, there could be issues as the
snow melts and rainfall causes ponding of water on roadways. Snow
levels are expect to rise to around 3500ft over the southern
panhandle and to around 1500-2000ft over the north by Friday
afternoon. White Pass could even see rain mixed in with these warm
temperatures. Snow level and temperatures were raised some to
reflect this idea. Widespread rainfall looks to continue through
Friday but winds will gradually ease.

Models were in good agreement over the next couple days. The 12z GFS
was not available for most elements, but it compared well with the
NAM which was used for the minor adjustments made. Forecast
confidence is above average.

.LONG TERM...ISSUED AT 605 AM Wednesday.../Thursday through
Tuesday night/ A high end gale force low is forecast to enter the
western gulf on Thursday. Gale force winds with the associated
front will arrive over outer coast on Thursday evening and extend
from Cape Suckling south past the Dixon Entrance. Peak conditions
expected on the inside late Thursday night with gales forecast
for Clarence Strait, Sumner Strait, southern portions of Chatham
Strait, and Cross Sound. Elsewhere on the inside, small craft
winds forecast except for northern Lynn Canal, where a parallel
gradient should result in winds 20 kt or less.

Precipitation from this front will arrive along the outer coast
late Thursday afternoon or Thursday evening. Significant low level
warm air advection associated with this front will push snow
levels higher, limiting snow to the higher elevations of the
highways.

WPC, the 00Z GFS, and the 12Z ECMWF model runs presented moderate
to good agreement at 500 mb on the placement of troughs, short
waves, and upper level ridges. A ridge extending from BC southwest
to coastal waters west of Washington State will become suppressed
over the weekend but then rebuild early next week. Temperatures
from Thursday into Friday were warmed slightly.

Confidence in the extended range forecast is average.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Gale Warning for PKZ052.
     Small Craft Advisory for PKZ022-033-041>043-051-053.
&&

Ferrin/Bezenek/Fritsch

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