Small Craft Advisory 344, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...UPDATED
National Weather Service Anchorage AK
600 PM AKDT Sun Apr 30 2017

.ANALYSIS AND UPPER LEVELS...
A trough moving north across the Northern Gulf is kicking off
showers across Southcentral. In addition, gusty winds are evident
along Turnagain arm, Knik River Valley, and along the Copper
River. A weather front, associated with a pair of lows over the
central and eastern Bering Sea is bringing rain to Bristol Bay
and over the southern and western Gulf including Kodiak island.
Gusty easterly winds are evident in advance of this front from the
western Gulf to the eastern Kuskokwim Delta with fairly brisk Gap
flows through the Aleutian range.

&&

.MODEL DISCUSSION...
With the exception of a developing low heading north into the Gulf
Tuesday, the models are in good agreement through Tuesday
afternoon. The NAM is the weaker and farthest north of the model
solutions by taking the low into the southeastern offshore marine
zone Tuesday afternoon. The remaining models have a stronger low
much further south at this time (Tuesday Afternoon). For now will
lean closer to a GFS/EC with this feature.

&&

.AVIATION...
PANC...Visibilities and ceiling will remain VFR. However, gusty
southeast winds this afternoon are expected continue through this
evening before diminishing. The surface wind direction should back
around to the northwest early Monday morning. On Monday afternoon
the surface winds shift back around to the southeast.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The frontal system currently moving over Kodiak Island will usher
in the beginning of a cloudier weather pattern for most of
the area that will last into mid-week. Ahead of this front, a
weakening pressure ridge along the gulf coast will bring gap winds
to Turnagain Arm and the Knik River Valley, which will also bring
gusty southeasterly winds to the Anchorage Bowl and Palmer areas
this evening. The front will then move into the northern Gulf on
Monday, bringing widespread rain to the southern Kenai/Gulf Coast.
Inland areas will remain largely dry from downsloping ahead of the
front, but downsloping will weaken as cold air moves in aloft,
which should allow for a few rain showers to develop. This cold
air aloft may also produce a few thunderstorms to Kodiak Island
overnight tonight, which would then spread northward into the
Kenai Peninsula in the afternoon/evening. Confidence is low on the
development of these thunderstorms as instability is quite
marginal with cool temperatures in the Gulf, but a few strikes
also can't be ruled out.

The active weather pattern will continue on Tuesday as a strong
gale force low moves into the central Gulf through Wednesday.
There still is some uncertainty in the exact placement of this
low, but there is increasing confidence that the low will remain
far enough south to keep much of the impacts over land limited to
the Gulf Coast. More importantly, there is very good agreement
that this low will bring widespread gale or potentially storm
force winds along with seas upwards of 20 ft to the Gulf that will
last into Wednesday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
With the main low hanging out in the vicinity of the Eastern
Aleutians and Alaska Peninsula, southwest Alaska will stay under
predominately southeast flow. This pattern will also keep the area
unstable with showers continuing into Tuesday. The strongest
showers will be Monday afternoon over the Bristol Bay area as a
trough pushes through from the south. It is borderline, but there
will be a slight chance of thunderstorms popping up around the
Bristol Bay area as it moves through Monday afternoon.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
As the low near the Eastern Aleutians and Alaska Peninsula slowly
tracks southeast it will bring northerly flow and showery
conditions to most areas of the Bering and Aleutians. The
exceptions will be areas under the effects of ridging that is
moving in over the Western Aleutians. This ridging looks to make
it to the Central Aleutians by Tuesday evening with another low
following behind from the west.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The storm in the Gulf on Thursday will slide inland into south
central Alaska by Friday. An upper level low south of the central
Aleutians on Friday will slowly move east through next weekend.
This will carry a surface low and frontal boundaries eastward and
northward through the period, focusing rainfall along the
Aleutians initially and then through south central Alaska on the
weekend. Blended towards the GFS early (Thursday into Thursday
night) then utilized the guidance from WPC, which was a blend of
the deterministic and ensemble means from the GFS and ECMWF.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 119 130 131.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...DEK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK