Small Craft Advisory 240, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
420 AM AKDT Tue Mar 21 2017

.ANALYSIS AND UPPER LEVELS...
The blocking ridge remains over the eastern Bering with a trough
to its east stretching north and south through Southcentral
Alaska. The trough is bringing snow to areas around the north
Gulf coast, but the ridging has kept it away from the Cook Inlet
area. To the west of the ridge a low is tracking north to the west
of the Western Aleutians bringing rain and snow to the area.

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.MODEL DISCUSSION...
The models are in good agreement through the mid term with only
minor variations with low placement moving into the mid term.

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.AVIATION...
PANC...VFR conditions and light winds will persist.

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.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The upper level trough is holding firm over Southcentral Alaska
along a north-south line from near Cantwell to Seward and then
into the western Gulf of Alaska. This will keep precipitation
east of the trough and confined to the north Gulf coast today with
everything shifting slowly eastward the next few days.

A weak surface low in the Gulf is increasing the gradient over
Prince William Sound with the strongest winds expected in the
Thompson Pass area today. There will be some gusty winds through
channeled terrain in the Alaska Range but not as strong as the
Prince William Sound area.

This also means that Anchorage and other areas west of the Kenai,
Chugach and Talkeetna mountains will remain mostly sunny during
the days and clear at night. In summary: Not much change in the
weather over the next few days.

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.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The Bering Sea ridge will continue to support dry northerly flow
over the southwest mainland through the middle of the week. This
means more of the same across the area, with sunny skies and
diurnally driven gusty winds during the afternoon. Temperatures
will remain below seasonal norms, with overnight lows continuing
to dip near zero as a result of more optimal radiative cooling
processes owing to clear skies and subsiding winds.

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.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The strong blocking ridge over the eastern Bering will continue
to dominate the pattern through the next few days. This will
bring more sunshine to the Pribilofs, Eastern Aleutians, and
Akpen, though some marine stratus may still sneak in at times. A
weak front extending from a low near the Kamchatka Peninsula will
continue to bring rain and Small Craft Advisory conditions to the
Western Aleutians through Wednesday before lifting north of the
area. A weak wave south of Adak will also bring light rain to the
central part of the chain through Wednesday night.

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.LONG TERM FORECAST (Days 3 through 7/Wednesday night through Monday)...
The blocking ridge will remain firmly entrenched over the Bering
Sea until next weekend when it appears this long pattern (which
has been in place for all of March) will finally break down. Until
then, expect continued mostly dry and cool conditions over the
southern mainland. A series of short-wave troughs dropping down
from the Arctic will re-supply cold air and lead to occasional
increases in winds later this week, especially along the Gulf
coast and Alaska Peninsula. A semi-permanent surface low will set
up over the east or northeast Gulf. As short-waves dive into
Southcentral they may tap into some of this moisture and spread
some light snow northward to portions of the Copper River Basin
and eastern Prince William Sound.

Meanwhile, a strengthening subtropical jet will undercut the
upper ridge, driving eastward across the north Pacific Friday
through Saturday. With a weakened ridge left in place over the
eastern Bering, this will allow a deep storm system to move to
the Aleutians Thursday night and Friday. More significantly, this
storm will then progress eastward along the Aleutians and Alaska
Peninsula next weekend as the upper ridge retreats to the Arctic.
This will open the way for precip and warmer air to move into the
southern mainland as soon as early next week.

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.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...None.

&&

SYNOPSIS AND MODEL DISCUSSION...DK
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
LONG TERM...SEB