Small Craft Advisory 249, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
302 PM AKDT Tue Apr 17 2018

.SHORT TERM.../Through Thursday/...A weakening surface low over
the northern Pacific will lift a weather front through the
panhandle tonight, which will produce moderate southeasterly winds
Tuesday night through Wednesday along the outer coast. Along the
Aleutians a stronger upper low associated with an active Pacific
jet will continue to push eastward into the gulf and the
associated stronger front will move into the eastern Gulf by
Wednesday night.

After a day of plentiful sun, clouds will begin to increase from
south to north across the panhandle tonight indicating the
beginnings of an extended wet pattern. Visible satellite this
afternoon indicated some convective activity across Prince of
Wales Island producing a few isolate showers. As the front
approaches from the south the atmosphere will stabilize and merge
with the stratiform deck tonight.

With the regime change from dry to wet, a few items captured our
attention during this period: the timing of the onset of the
precipitation and associated front as well as precip type in the
northern portions of the panhandle. We expect snow to mix with
rain with the onset of precip early Wednesday for the Icy Strait
Corridor including Juneau. However, accumulations will be
negligible because temperatures will marginally reach the freezing
point. We also expect impactful late season snowfall along the
Klondike Highway near White Pass with up to 9 inches of snowfall
during a 36 hour period from Wednesday morning through Thursday
afternoon. As the stronger low develops in the Gulf on Thursday,
an area of stronger vorticity and higher lapse rates may lead to a
more convective shower with moderate amounts of rain along the
inner coast.

Finally winds across the gulf will increase slowly to 25 to 35 kt
through Wednesday night as the front approaches. Likewise
southerly winds through the Inner Channels are also still
scheduled to rise through the period. With good model agreement
we made few if any changes through Thursday. However, some lighter
winds were adjusted in the evening to account for some delays in
the marine push advecting northward.

Models were for the most part in good agreement with each other,
so we leaned toward a blend of the NAM/ECMWF/Canadian to adjust a
few of the weather fields. Also tweaked the temperatures a bit
with a mix of the NAM/EC MOS guidance. Forecast confidence is
above average for synoptic pattern.

.LONG TERM.../ Thursday through Monday / One word pretty much sums
up the entire long range forecast: WET. Thursday remains on track
for rain across the Panhandle, decreasing some on Friday, then
increasing in coverage again for the weekend. Rain over the
Panhandle continues into the new work week, as well.

The winds have SCA for most of the gulf and Clarence Strait to
start out Thursday. Gales are possible for the Cape Suckling area
early Thursday morning and increasing to gales for Clarence
Strait. By Friday the occluded front will be out of the area and
winds will be down to 15 kt or less. These conditions will
continue until the next system starts moving in by Sunday
bringing 20 kt to our western area in the central gulf and then
spread east and increasing to SCA for the outside waters on
Monday.

Model agreement was fair, the Canadian and ECWMF was the primary
tool used to update the forecast slightly, mainly for timing for
Thursday through Saturday. Sunday and Monday the ECMWF and WPC
took top billing. Overall forecast confidence is above average for
the large scale features of the wet and weak weather pattern for
the weekend.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ052.

&&

DDH/JWA/KV

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

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