Small Craft Advisory 369, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
457 AM AKDT Sun May 7 2017

.ANALYSIS AND UPPER LEVELS...
Early this morning a stacked low spinning south of Kodiak is
bringing gale to storm force winds along the western gulf waters
with precipitation stretched along its boundary, extending from
the southwest mainland to the northeast gulf. The surface low is
slowing as it nears the southern mainland with the upper level
front pushing north and west. To the west, rather benign
conditions are across the western Bering as a ridge builds in from
the North Pacific.

&&

.MODEL DISCUSSION...
Models were in good agreement with the synoptic pattern through
the short range. The high resolution of the NAM was used to make
minor changes through Tuesday. The main challenge was focused
around the low making landfall today bringing gusty winds and
rain as it tracks along a counter-clockwise pattern into the
eastern Bering tonight and then southeast back into the North
Pacific by Tuesday.

&&

.AVIATION...
PANC...VFR conditions prevail through the next TAF package with
downsloping southeasterly flow across the Chugach keeping west
Anchorage dry. The front along the gulf moves slowly inland this
morning with a low level jet developing along a tightening
pressure gradient along the coast. Once the front pushes through
southeasterly winds mix down to the surface through the evening
then taper off overnight as the surface low moves across to the
eastern Bering. The timing of the wind gusts may need to be
adjusted as there is some uncertainty of the frontal passage.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
A weather front over the northern Gulf of Alaska will weaken along
the Gulf Coast through Monday. Strong southeasterly cross-barrier
flow across the Chugach Mountains will keep most of rain along
the coasts with sprinkles or a few stray showers to the west.
Strong gap flows through Turnagain Arm and Portage Valley will
diminish through this afternoon. Locally brisk and gusty gap
flows are expected through the Knik River Valley and along the
Copper River during the afternoon and early evening hours today
and to a lesser extent on Monday.

&&

.FIRE WEATHER...
Near critical fire weather conditions are expected during the
afternoon and evening hours today out Knik river and along the
Copper river, with gusty winds (to 25 mph) and low RH's below 30
percent. Temperatures however are expected to remain below 65
degrees. On Monday, gusty afternoon and evening winds are likely
to redevelop, but should not be as strong as today and
temperatures will once again remain below critical values.

&&

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

Everything is on track with an area of low pressure forming south
of Kodiak Island this morning. The King Salmon NEXRAD currently
shows rainfall beginning to overspread the Bristol Bay area but it
looks like downsloping has begun to win out for locations between
Iliamna and Dillingham. This developing low pressure system will
move across the Alaska Peninsula late this morning into early this
afternoon which should allow rainfall to taper off across
Southwest Alaska. As the low translates into the Bering Sea, the
downslope component off the Alaska and Aleutian Ranges will weaken
which may allow a few showers to develop near King Salmon.
Otherwise, this low pressure system is forecasted to track back
into the Pacific Ocean on Monday which will allow the thermal
trough over interior Alaska to nose over portions of Southwest
Alaska. It looks like convective showers will be possible on
Tuesday but the lack of mid-level instability should help inhibit
any thunderstorm chances at this time.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

A low pressure system south of Dutch Harbor will merge with a
developing area of low pressure system near Kodiak Island. This
will allow rainfall to continue across the Eastern Aleutians and
Pribilof Islands until the resultant low moves into the North
Pacific on Monday. By Sunday night, the next frontal boundary will
be moving into the western Bering Sea as an area of low pressure
tracks eastward off the Kamchatka Peninsula. Models are hinting at
pretty sizable PWAT values and are showing quite a bit of QPF
with this front. Gale force winds are expected to develop over the
western Bering Sea on Monday but should quickly weaken as it
shifts eastward.

&&

.LONG TERM FORECAST (Days 3 through 7)...
A vertically stacked low pressure system south of Nikolski will
slide eastward throughout the day while weakening, as a triple
point low develops south of the Alaska Peninsula late this
afternoon. This newly developing system will result in gusty
winds through Shelikof Strait and across portions of the Alaska
Peninsula, as well as bringing another round of rainy conditions
to the area. These two low pressure systems will merge Sunday
afternoon, and gradually weaken over the north Pacific while
slowly tracking eastward toward the Gulf of Alaska. The next
frontal system will approach the western Aleutians/Bering Sunday
afternoon, as a low pressure system pushes off the coast of
Kamchatka. A weak triple point low will develop just west of the
western Aleutians Monday morning, as the associated front begins
tracking through the Western Aleutians/Bering. This system will
bring gusty winds and rain to the area as it tracks eastward
during the day monday. The front will then dissipate by Tuesday
morning over the central Aleutians and Bering, as the parent low
dissipates over the western Bering.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORMS 130.
         GALES 119 120 125 131 138 139 174 178.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KH
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MC
LONG TERM...LF