Small Craft Advisory 181, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
437 AM AKST Wed Feb 28 2018

.ANALYSIS AND UPPER LEVELS...
Clear skies prevail across much of the southern mainland this
morning as a disturbance diving out of the interior helps to dig
the longwave trough along the Alcan border and amplify the upper
level pattern. Cold air advection behind this feature is aiding in
the development of a strong outflow wind regime across
Southcentral Alaska, with additional support from a 140 kt jet
streak sliding east across the mainland as it moves down the back
side of the trough. This is producing gale force winds with storm
force gusts over portions of the North Gulf Coast, along with
warning level winds through Thompson Pass. Quiet weather prevails
across the eastern Bering beneath a stout high amplitude ridge
which extends from the subtropical Pacific all the way to the
North Pole. Farther west, a powerful 948 mb low is tracking
parallel to the Kamchatka coast, with an occluded front moving
into the Central Aleutians accompanied by rain and southerly gale
force winds.

&&

.MODEL DISCUSSION...
Models are in excellent synoptic agreement through the end of the
work week as the Bering ridge shifts eastward to the mainland,
eventually bringing an end to the outflow winds across
Southcentral. This will allow the front to continue its eastward
push and reach the southwest coast by Thursday, with showery
southwest flow setting up in its wake. Primarily utilized higher
resolution NAM guidance to better capture localized outflow wind
effects.

&&

.AVIATION...
PANC...Gusty north winds should diminish somewhat this morning as
the most favorable upper level support moves off to the east. VFR
conditions will prevail through the TAF period, although ceilings
may briefly fall below 5000 ft prior to 15z as an upper level
disturbance departs into the Gulf.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Strong offshore winds will dominate today along the Gulf coast and
Prince William Sound as Arctic air continues to advect southward
on the back side of the trough/low dropping into the eastern Gulf.
As a strong upper level ridge approaches from the west, the upper
level jet will slide eastward, with the strongest winds and downward
motion shifting to eastern Prince William Sound. A high wind
warning is in effect for Thompson Pass through this afternoon
for gusts up to 80 mph, but there may be a few peak wind gusts of
similar strength which make it down into Valdez. While the bulk of
wind will be along the coast, there will be some wind today along
the Alaska Range as well as across the Copper River Basin. Winds
will very slowly diminish from west to east tonight through
Thursday as the ridge builds in.

Temperature will vary significantly across short distances, with
warmer temperatures where the wind causes vertical mixing and
colder temperatures where the absence of wind allows for
radiational cooling. A lighter wind regime and upper level ridge
position appears to favor very cold temperatures Thursday night.
However, it looks like mid to high clouds will move into western
areas (Cook Inlet to Susitna Valley corridor). This will help
moderate temperatures just a bit, though they will still bottom
out in single digits for most areas.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA...
Ridging continues to build in over southwest Alaska from the
Bering which has cleared out much of the cloud cover and allowed
for temps to plummet. As the ridge axis shifts east of southwest
Alaska late tonight warm air will begin to be ushered in from the
south. This will be followed by a front moving in over the coast
Thursday afternoon which will bring short lived blowing snow
conditions to the Kuskokwim Delta coast. The front will then track
eastward as it breaks apart. Friday afternoon another ridge will
build in over the area from the Bering.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS...
The main feature over the Bering and Aleutians is a low in the
western Bering and its associated front that stretches across the
central Bering and Aleutians. This system is pulling up enough
warm air that the majority of precip associated with the front is
rain. The front will slowly track east through Thursday making it
to the eastern Bering Thursday afternoon before heading over
mainland Alaska. Behind the front, cold westerly flow will
dominate until ridging builds in Friday afternoon. Behind the
ridging, another system will approach the western Aleutians
bringing more rain to the islands.

&&

.LONG TERM FORECAST (Days 3 through 7)...
At the onset of the forecast period, there is a closed low south
of the AKPEN with a ridge axis upstream bisecting the the Chain
and spanning into NE Russia. As time elapses, the ridge axis will
shift eastward and an Arctic vortex will descend from Siberia and
into the Bering. By Day 6 (Monday March 5th) a new ridge will
build in from the North Pacific bringing warmer temperatures to
the Western and Central Aleutians. The GFS has maintained decent
run to run continuity with the major synoptic features. Very
confident in the progressive nature of the pattern. West Domain
(Bering Sea, Aleutians and SW AK) sensible weather highlights
include gale force winds across portions of the Bering in
association with the frontal boundary Saturday and Sunday. East
Domain sensible weather highlights include a batch of wintry
precipitation for Kodiak and the southern Kenai Saturday March 3rd
that will move across the Gulf Of Alaska later Saturday and Sunday
but will remain south of Anchorage. Monday a new batch of wintry
weather is anticipated to impact Kodiak with moisture working its
way up Cook Inlet later Monday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 131
MARINE...Storm Warning 130 178 411
 		 Gale Warning 119 120 121 125 127 128 129 131 132 136 137
					  138 150 165 170 172 173 174 175 176 177 179
					  180 181 185 351 352 412 413 414
		 Heavy Freezing Spray Warning 130 139 160

&&

SYNOPSIS AND MODEL DISCUSSION...CB
AVIATION...CB
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...PJS