Small Craft Advisory 250, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
425 PM AKDT Fri Mar 24 2017

.ANALYSIS AND UPPER LEVELS...
A large and deep vertically stacked low about 330 miles south of
the Western Aleutians is drifting northward along with an east-
west oriented occluded front just out ahead of the low center.
This is producing widespread rain and gale force winds along the
Aleutians and into the southern Bering Sea. Meanwhile, the strong
blocking ridge over the northern to eastern Bering Sea continues
to provide dry and cool conditions for the remainder of the
forecast area, from the eastern Bering Sea and Alaska Peninsula
to the southern mainland and Gulf. The trough which was centered
over Southcentral has shifted eastward, though a short-wave
dropping down the back side is bringing another weak shot of
arctic air and leading to an uptick in gap winds along the coast.

&&

.MODEL DISCUSSION...
As expected, the models are struggling with the transition in
pattern. Over the next couple days, the subtropical jet drives
eastward across the North Pacific leading to the development of
multiple deep lows. Models quickly diverge on the exact track
of the low centers. Fortunately, through the weekend the track of
theses storms will be far enough south that forecast uncertainty
primarily affects coastal waters south of the Aleutians/Alaska
Peninsula. Have generally used a NAM/GFS blend to provide a nice
middle ground solution. For the remainder of the forecast area,
forecast confidence remains high through the weekend.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
An upper level trough continues to drop down from the north as
it swings through the Southcentral region. Look for possible snow
showers over the northern Gulf eastward through the Copper River
Basin through this weekend. Otherwise, continued offshore flow
with mostly sunny skies for the Anchorage Bowl through Saturday
before some mid-to-high clouds move into the area by Sunday.
Meanwhile, the gradient begins to weaken but will have the usual
gusty gap winds through Whittier, Valdez, and Thompson Pass
regions.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Clear and dry conditions will persist through the weekend, as a
strong area of high pressure and offshore flow continues to
dominate the sensible weather over the region. Continue to expect
sunshine and seasonable temperatures during the day and cool
temperatures at night. While the winds will keep nighttime lows
from dropping as far as they could, the resultant wind chills will
keep things quite chilling over the mainland. For the next
several nights, wind chills in most areas are aiming for a few
degrees on either side of 10 below. However, twelve and a half
hours of daylight (and counting) will still make for healthy
temperature recoveries well into the 20s during the day under
mostly sunny skies.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A gale force front continues to stall and weaken over the Western
and Central Aleutians through Saturday, as the parent low weakens
and halts its approach to the western Aleutians. Showery
conditions and gusty southeast winds will persist over the Western
and Central Aleutians/Bering through much of the weekend, while
the Eastern Bering begins to slowly gain more sky cover. By
Sunday, another low will advance any heavier precipitation further
east into the eastern Aleutians, but a very stubborn high
pressure system over the northern Bering will curtail significant
northward progression for any areas of precipitation and
associated low pressure systems.

&&

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

Ridging over the Bering will slowly retreat to the north as a
front slides north across the Aleutian chain through the end of
the weekend. Real change continues to be advertised by all models
early into next week. All guidance has shifted the focus of a low
that would have only impacted the panhandle to bringing the low
much farther north and into the Gulf. There are still some pretty
sizable differences amongst the guidance types that detail how
strong this low will be and what, if any, precipitation may fall
across the anchorage area. At this time, confidence is too low to
go any higher than a slight chance of snow. The bottom line is
that the pattern is now on the verge of change and the days of
cold and endless sun are going on a brief hiatus. The longwave
patter undergoes a bit of a shift following this early week system
and will set us up to be in a little bit of a favorable patter to
see systems beyond the forecast timeframe reaching all of south
central.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Heavy Freezing Spray...121 139 185 Gale Warning...170
172 173 174 175 176 177 178 .

&&

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...PD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PEPE
LONG TERM...SS