Small Craft Advisory 544, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
444 AM AKDT Wed Jul 19 2017

.ANALYSIS AND UPPER LEVELS...
An upper level low is currently centered over the northern
Bristol Bay coast and is moving southeast. A surface low is
located over Kodiak City and is slowly moving northeast while
dissipating. An occluded front associated with the upper low is
draped across southcentral Alaska with a wide swath of
precipitation extending from the upper Susitna Valley south into
the Gulf. The trailing precipitation edge is currently moving
northeast across the Kenai Peninsula, with rain tapering off at
the cities of Homer and Kenai. Further west, areas of rain and
showers underneath the cold core center of the upper low are
moving over southwest Alaska. An upper level ridge of high
pressure is moving east into the western Bering Sea as a weak
upper level low over the western Aleutians transits east with the
associated surface front spreading rain and showers across the
island chain.

&&

.MODEL DISCUSSION...
Models have come into better agreement with the location and
movement of the surface low moving into the Gulf of Alaska on
Thursday. The consensus is to bring the low southeast into the
North Pacific, well out of our AOR, while building an upper level
ridge from the Eastern Bering east into mainland Alaska by the
weekend. Small differences in model solutions at this time will
have little impact to the overall forecast for the AOR.

&&

.AVIATION...
PANC...Rain will begin to taper off this morning as VFR
conditions persist through the period. Southeasterly flow will
increase this afternoon but winds funneling out of the Turnagain
Arm will mostly be deflected to the southwest away from the
terminal. There may be a brief period of higher southeast winds
in the evening but these should subside shortly thereafter.

&&

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

The sounding this morning indicates deep southeasterly cross
barrier flow and drier lower levels as a result. This downsloping
helps to explain why radar has indicated persistent steady
rainfall over Anchorage overnight, but rain has been very light.
This cross-barrier flow is expected to persist today and should
help to limit rainfall throughout the day and tomorrow as well. In
upslope places such as Seward, expect rainfall to continue to be
steadier. In addition, the associated coastal jet should help to
keep Prince William Sound well within the small craft advisory
category with gusty winds. Rainfall will gradually diminish across
much of southcentral as the front slowly weakens, however
pressure gradients will remain strong enough to sustain the
coastal jet through Thursday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The low over southwest Alaska will continue its track south and
make it into the North Pacific tonight. Until then it will bring
more rain to southwest Alaska with the heaviest around Bristol
Bay. High pressure will then build in over the area from west
which will cut off most of the rain. However, afternoon showers
are still expected, especially along the mountains.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Westerly flow will dominate the early part of the day with a low
tracking through the flow from the west. This low looks to make it
to the Western Aleutians this afternoon and to the Central
Aleutians tonight before pushing south into the North Pacific.
Behind the low, ridging will build in from the western Bering and
then extend over the northern Bering. On Thursday it will
cover a majority of the Bering keeping winds relatively light
while bringing a widespread threat of stratus and fog to the
area.

&&

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

The stacked low pressure system over the Alaska Peninsula late on
Thursday will continue to drop south into the North Pacific and
Western Gulf of Alaska by Friday morning. Models begin struggling
on how quickly this feature shifts eastward as well as how far
north the feature tracks. At the time, the subtropical jet looks
rather weak which tends to support a slower movement (depicted by
the GFS) which keeps the low pressure system away from the
northern gulf coast. However, the ECMWF and some of the ensemble
members show a jet streak developing within the subtropical jet
which could push this system toward the Panhandle by the end of
the weekend. With poor model agreement, forecast confidence with
this is quite low. However, teleconnections and models are hinting
at longwave ridging developing over the Bering Sea and nudging
into the Alaska mainland throughout the upcoming weekend. The
amplitude of the ridge is rather unimpressive but the wavelength
hints at the potential for long duration ridging over the Bering
Sea. This should allow for some clouds to clear across Alaska and
the Bering Sea through the weekend although fog may become an
issue at times, especially with the wet pattern currently
unfolding. The low amplitude ridge will allow for some weak upper
level disturbances to push inland through early next week which
could bring a few periods of showers but confidence with any given
disturbance is low 5 to 7 days out.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KV
SOUTHCENTRAL ALASKA...EN
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...JW