Small Craft Advisory 294, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
437 AM AKDT Sun Apr 8 2018

.ANALYSIS AND UPPER LEVELS...
Water Vapor satellite imagery shows a ridge centering over the
interior early this morning with a broad closed low south of the
Alaska Peninsula. Further west another parent low, spinning just
south of the Kamchatka Peninsula, is pushing a storm force front
into the western Aleutian Chain. This storm is currently bringing
gale force southeasterly winds across the western Bering along
with rain. The low south of the Alaska Peninsula is a weaker
system, however it should be monitored as it is expected to
organize on a northward track late Monday.

&&

.MODEL DISCUSSION...
Models are in good agreement with the synoptic pattern through
Monday. However, they begin to diverge on solutions for a
northward moving front expected to move into the Gulf Monday and
Tuesday. The NAM and GFS solutions had the slowest progression of
the front and were in best agreement. The ECMWF and Canadian
models were most aggressive with the low and differed greatly on
the track of the system. The NAM was used to make updates for the
morning package as the slower solution is most probable as the
ridge over the interior will likely hold its position through
Tuesday.

&&

.AVIATION...
PANC...VFR conditions and light winds are expected to prevail
through Monday morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A broad upper level trough over the Gulf will lift northward
across the Gulf today and then across Southcentral tonight into
Monday. Still expect quite a bit of sunshine today across most of
Southcentral, with just some cirrus clouds high up. Clouds will
lower tonight, with precipitation developing along the north Gulf
coast and Prince William Sound. With weak vertical motion and a
dry air mass in place inland, don't expect any precip to survive
the trip over the coastal mountains.

A deep low over the northeast Pacific will then head northward
tonight, with a second low forming out ahead of the original,
preceded by a warm front. With ridging building out ahead of
this storm system and storm motion stalling as the low becomes
vertically stacked, it's looking like the bulk of rain and wind
will be confined to the Gulf and Kodiak Island. Western Prince
William Sound and the north Gulf coast may see periods of rain
and snow as well, depending on how far north the frontal system
makes it. A lot of the moisture with this storm system will head
toward Kodiak Island, so expect a long duration of rain Monday
through Tuesday night. Expect at least an inch or two of rainfall,
though if the front stalls over Kodiak it could be more like
three inches. For the bulk of Southcentral, dry conditions will
persist with a mix of sun and clouds and warmer than normal
temperatures.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
High pressure over the mainland will keep Southwest AK dry through
Monday afternoon, as offshore flow maintains mostly clear skies.
There is some potential for patchy fog development over the next
few nights as high pressure settles in within a weak warm air
advection regime. However, the continued offshore flow and dry
ambient conditions will serve to keep any fog localized in nature
to portions of Greater Bristol Bay and the Kuskokwim Delta. The
chance for precipitation will return to coastal areas by Monday
evening, as a weakening Bering front approaches the mainland.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Wet and windy weather conditions are expected to pick up this
morning over the western Aleutians/Bering as the next front
tracks in from the west. This system will spread precipitation and
stronger winds from west to east across the Bering and Aleutians
through Monday evening as it tracks eastward into the southwest
coast. Storm force winds will develop over the Western Aleutians
and surrounding waters by this evening as the parent low moves
into the Bering, aided by cold advection on the back side of the
system. The strongest gusts will remain in this corridor on the
southern periphery of the low, stretched across the western and
central Aleutians through Tuesday morning.

&&

.LONG TERM FORECAST (Days 3 through 7)...
(Previous discussion)
The weather pattern this week will undergo a gradual transition
as the weakening ridge over Mainland Alaska is pushed north and
large scale upper level lows along the Aleutians and over the Gulf
of Alaska become the dominate weather features to influence
southern Alaska. Early in the week, an upper low over the Bering
and one well south of the Gulf will merge Tuesday into a broad
multi- center low over the Gulf as the two features track east and
north respectively. Troughs and associated surface lows will
rotate through the Gulf around the periphery of the broad low
Tuesday and Wednesday.

The next low coming in from the west will track along and south
of the Aleutians Tuesday night and Wednesday to get pulled into
the large scale Gulf/North Pacific upper low low circulation
around around Thursday. By Friday another equally large upper
level low will become established centered off of the Kamchatka
Peninsula but extending over the western Bering, western Aleutians
and extending well south into the Pacific. The presence of these
two large upper level lows will help to amplify the upper level
ridge building in between them over the central and eastern
Aleutians and Bering on Friday.

By Saturday the upper ridge shifts east to the Alaska Peninsula
and Southwest Alaska and then continues to build over Mainland
Alaska Sunday and Monday with developing north Pacific frontal
systems starting to push back into the Aleutians around this time.
The net effect of all of this looks like continued relatively
quiet weather with a gradual warming trend through the week
(though dependent on cloud cover for how much of a warming trend)
and the potential for more rapid warming next weekend if the upper
level ridge does indeed push east over Mainland Alaska.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm 178.
         Gale 173 174 175 176 177 185.
         Heavy Freezing Spray 181.

&&

SYNOPSIS AND MODEL DISCUSSION...KH
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...JR