Small Craft Advisory 350, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
818 AM AKDT Tue May 2 2017

.ANALYSIS AND UPPER LEVELS...
The "anchor" in our flow pattern aloft so to speak is an upper
level low pressure centered over the Alaska Peninsula. The jet
stream is amplified, but still lies well south of the Aleutians.
While the longwave trough is controlling the flow, a shortwave
feature is what catches the eye on water vapor imagery this
morning. A strong disturbance is seen taking shape in the north
Pacific/southern Gulf, entering the eastern side of the longwave
trough. That disturbance and associated strong surface low will be
the focus for active weather in the short term.

Currently a trough rotating around the longwave has cleared
Southcentral AK leaving a short-term showery regime in it's wake,
but middle and high clouds are already streaming out ahead of the
Pacific low and toward Southcentral, so there won't be much of a
break before these clouds move in.

&&

.MODEL DISCUSSION...
Synoptically, guidance is in great agreement with the developing
Gulf system having similar tracks and strengths of the lows
through the short term. Some slight positional differences start
to arise on Thursday after the system begins to weaken and move to
the east.

&&

.AVIATION...
PANC...uncertainty early on in the TAF revolves around how
quickly the Turnagain wind quits, but there is higher confidence
that winds will go northerly pretty quickly this morning.
Otherwise fairly high confidence through the period.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Conditions will rapidly deteriorate across the Gulf of Alaska
waters and Kodiak Island today as an unusually strong late season
low tracks up from the Pacific and into the Gulf. The bulk of
steady rain will initially remain offshore of the north Gulf
coast/Prince William Sound due to northerly flow out ahead of it.
However, the occluded front will gradually back its way onshore
tonight bringing increasing winds and rain. Flow will then shift
around to the east on Wednesday as the low makes its way
northward across the Gulf. This will bring steady rain to Western
Prince William Sound.

Meanwhile, much of interior Southcentral will start out today with
some sunshine. This will destabilize the boundary layer once
again and lead to gusty north winds this afternoon and evening as
some wind from aloft mixes down to the surface. As the front moves
onshore tonight and goes aloft, the mid to upper levels will
become more unstable. Expect a good chance of showers most places
with this front. Behind this, general instability will favor
mainly diurnal showers (afternoon/evening hours). The Gulf storm
will slowly lose steam over the Gulf as we head through the
remainder of the week.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Showers will be more limited today as a large low tracking
northward into the Gulf quickly becomes the dominant feature and
pulls the upper low over the Alaska Peninsula southward. A trough
rotating through the lower Yukon River in the afternoon will
bring the potential for isolated thunderstorms to the Kuskokwim
Delta this afternoon and evening. North to northwesterly winds
will increase tonight through Wednesday morning for a rather dry
and windy day Wednesday, especially around the greater Bristol Bay
area. Winds will diminish Thursday, however conditions will
remain dry with the exception of a north to south running band of
showers forming just to the west of the Alaska and Aleutian Ranges.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Upper level ridging over the western Aleutians will build east to
the central Aleutians today and tonight as a frontal system pushes
into the western Aleutians. As the ridge amplifies north across
the Bering low stratus and fog will become a concern underneath
it. The ridge will shift to the eastern Aleutians Wednesday night
and over the Alaska Peninsula Thursday as a somewhat stronger
front lifts north into the central Aleutians.

&&

.LONG TERM FORECAST (Days 3 through 7)...
On Thursday, the models are in fairly good agreement with holding
a weakening vertically stacked cyclone over the Gulf of Alaska
with several weak waves rotating around the center. This would
tend to keep most of the rain/showers across the Gulf though some
spotty showers will likely occur over the mainland with passing
upper waves. Ridging also looks to be over the eastern Bering Sea
with an upper low and associated surface cyclone heading toward
the western Aleutians.

By Friday afternoon, the Gulf cyclone has weakened and shifted
southeast. The upper ridge has now moved over Southwest Alaska
and the Aleutian cyclone is seen moving south of the eastern
Aleutians with its front spreading rain as far east as the
Pribilof Islands and Alaska Peninsula.

By Saturday afternoon, the ridge has now moved over the eastern
mainland and extends south across the east Central Gulf. The
cyclone near the eastern Aleutians has stalled but its frontal
system stretches east spreading rain to Southwest Alaska and the
western Gulf.

On Sunday and early next week, model solutions start to diverge
and the weather picture becomes a little more fuzzy. The main
difference is the evolution of a Rex Block (high over low) with a
ridge setting up over the mainland and a trough over the Gulf.
The ECMWF/WPC solutions tend to move the ridge over the mainland
fairly quickly north while the GFS keeps the ridge over the
southern mainland through Monday night. The ECMWF/WPC solutions
(preferred) would cause the upper trough to shift further north
allowing moisture to intrude into the southern mainland. The GFS
solution would delay the moisture intrusion until Tuesday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning 119 120 131 132
 		 Gale Warning 125 130 136 137 138 139 140 150 155 160.
FIRE WEATHER...NONE.

&&

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