Small Craft Advisory 550, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
908 AM AKDT Wed Jul 31 2019

.ANALYSIS AND UPPER LEVELS...
A ridge is currently over Southcentral Alaska this morning.
Upstream is an upper level disturbance in the eastern Bering with
a trough axis near Cold Bay. A second system is near the western
Aleutians. There are actually two trough/ridge couplets from
southeast Alaska to Shemya which underscores the progressive
nature of the weather pattern. A jet core moving into western
Alaska north of Bethel is associated with the arctic jet stream.
There is a second stream of jet energy undulating over the north
Pacific. The Bethel radar has detected precipitation between
Hooper Bay and Kipnuk early this morning. The Middleton Island
radar pinged into a few showers north of Cordova.

&&

.MODEL DISCUSSION...
The global and the mesoscale models are in good agreement with the
main synoptic features. The run to run continuity has been
consistent spinning up lows in the north Pacific and Bering. There
are some minor differences with the timing of the precipitation
shield with the next frontal boundary moving across the Aleutians
and into southwest Alaska. Overall the models look pretty decent
in the short term forecast period.

&&

.AVIATION...
PANC...VFR conditions and light winds are expected through
Thursday morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

High clouds will increase today though temperatures should still
remain warm with a pretty nice summer day over most of
Southcentral Alaska. The mid-level clouds will increase tonight
into Thursday as an upper level trough associated with an Arctic
low will move across Southcentral. The northern Susitna Valley is
the most likely place to see any rain with this system as most of
the energy will be in the interior of the state. A second upper
level wave is over the Alaska Peninsula this morning and will move
over Kodiak Island tonight before dissipating. After these waves
move through Thursday there should be another upper level ridge
building over the region. The big question with this ridge is
whether the seasonal upper level Arctic low transiting the Arctic
coast region will flatten the ridge and keep the area from
clearing the clouds out. Once again, the area most likely to see
rain later in the week will be the Susitna Valley.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3/Tuesday
afternoon through Friday afternoon)...

High pressure over the southwest gradually drifts eastward,
allowing a Bering low to move inland Wednesday morning. This will
bring cloudy skies, rain and southerly winds. As the low
progresses eastward through Wednesday evening, conditions will
improve briefly Thursday morning as a ridge of high pressure moves
over the southwest coast. By Thursday afternoon, a stout front
associated with a strengthening Bering low will push eastward.
This front will bring rain and gusty onshore winds, especially
along the Yukon-Kuskokwim Delta coast through Friday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through
3/Tuesday afternoon through Friday afternoon)...

A low centered north of the Aleutian Chain continues to track
eastward this evening bringing rain and southerly flow to the
eastern Aleutians. Behind this low, a ridge builds briefly,
allowing stratus and low level clouds to persist. By Wednesday
evening, a gale force front associated with a strengthening
Siberian low arrives over the western Aleutians, bringing another
round of rain and gusty southerly winds. As the front tracks
eastward through the end of the week, generally cloudy and
showery conditions are expected across the Bering through Friday.

&&

.MARINE (Days 3 through 5)...

Beginning the extended period marine forecast on Friday, there is
now very high confidence that a gale force low will move across
the Bering Sea into the Bering Strait. Longer fetch southwest
winds will bring seas up as high as 12-15 feet as the front moves
to the southwest coast Friday night. Another front will move into
the eastern Bering Sea Saturday evening into Sunday, keeping
seasonably strong 20-30 knot southerly/southeasterly winds from
the Pribilof Islands eastward.

Over the Gulf of Alaska, high pressure will weaken and westerly
offshore winds will increase late Friday and persist through
Sunday. The brunt of westerly winds will favor the Barren Islands,
Shelikof Straight and the southern coast of Kodiak Island.
Locally strong southerly winds will also favor southern Cook
Inlet, so mariners should be aware of higher local sea states.

&&

.LONG TERM FORECAST (Days 3 through 7)...

Beginning the long term period on Friday, there will be a flat
upper ridge over the southern half of the state with a series of
stronger upper southwesterly flow over the Bering Sea. This
pattern will be active as there is now high confidence that a
strong low will track into the interior of Alaska Friday and
Saturday. This will also bring in a swath of subtropical moisture
into southwest Alaska with periods of heavy rain and strong
coastal winds. Higher seas/surf will also impact the southwest
coast, especially the Kuskokwim coast where winds may exceed
40-50 MPH. The model trend lately has been for a stronger and
farther south track, and now there is increasing likelihood that
rain will also move into the Susitna Valley as these fronts move
inland through Monday. Thereafter, the numerical global guidance
keeps an active pattern over the Bering with fronts moving into
southwest Alaska and then the interior through Wednesday. This
will keep a similar "dirty ridge" pattern in place for
Southcentral, meaning quite a bit of clouds but generally dry
weather (with the exception of the Susitna Valley and the higher
mountains).

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 175 177 178 412 413.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BJB
MARINE/LONG TERM...JA