Small Craft Advisory 195, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
410 AM AKST Thu Feb 27 2020

.ANALYSIS AND UPPER LEVELS...

An area of high pressure at the surface and aloft continues to
remain centered over eastern Siberia, while extending into western
Alaska. To it's south, a pair of lows in the Gulf continue to
bring precipitation to portions of the Gulf Coast, mainly from
Prince William Sound to Yakutat.

Further west, a pair of lows was influencing the weather. The
first system was riding the Aleutians in an eastward trek, with
the low currently near Nikolski. Another low just north of Shemya.
Both of these systems were bringing some isolated showery type
precipitation to the region.

&&

.MODEL DISCUSSION...

The models remain in good agreement through the weekend in the
overall synoptic pattern, with the biggest difference being
related to a north Pacific low that moves into the western Bering
Sea saturday morning. Here, the GFS continues to be the strongest
solution (like it has been most of the winter), as it portrays a
964 mb low. Conversely, the ECMWF (European) model is almost 10 mb
weaker, with the Canadian in between in strength but shows two
different low centers in that vicinity. The net difference here is
how much coverage of storm force sustained winds there will be.

They (the numerical models) do show good agreement that a
disturbance aloft will pinch off from this system and eject
eastward, with cyclogenesis (the development of a low pressure
system) commencing in the Gulf by Sunday morning, but once again
they disagree on the strength of the system by 10 mb. This
scenario then repeats itself by early next week. So in short, an
active pattern looks to return to southcentral and southwestern
Alaska, westward through the Aleutians and portions of the Bering
Sea.

&&

.AVIATION...

PANC...VFR conditions and light winds will prevail through the
forecast period.

&&

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

High pressure building in from the northwest is clearing out skies
over Southcentral Alaska. A weak low near Middleton Island is
still pushing a few clouds along the north Gulf coast with a line
of showers toward Cordova early this morning. This area of
showers and clouds should diminish today as the low pushes to the
Southeast and away from the area. This should leave mostly clear
and cold conditions across most of Southcentral through Friday
night.

Friday night is when the next system makes its way to Kodiak
Island from the Southwest and then into the remainder of
Southcentral Saturday. This is the system that is expected to
bring widespread snowfall to Southcentral, with the exception of
Kodiak which will warm up rapidly to turn precipitation type to
rain. The development of a triple point low near the Barren
Islands on Saturday will keep the warmer air from pushing farther
northward keeping precipitation all snow for the rest of
Southcentral.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

In the past 24 hrs, the temperatures at Bethel and Aniak have
plummeted by more than 10 degrees. The models continue to show
northerly flow in the boundary layer thereby ushering arctic air
into the region. The models look bone dry for Southwest for today
and Friday. A new storm is churning up in the north Pacific and
the leading edge of the precipitation shield will be in Bristol
Bay and Toksook Bay Saturday morning.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

There is an elongated surface low from Unalaska to the Western
Bering that will continue to weaken and become absorbed into the
longwave pattern on Friday. A developing low will come charging
out of the north Pacific toward the Western Aleutians. The models
continue to show slightly different tracks and intensities with
the surface low but there is high confidence that the Western and
Central Aleutians will see high end gale force winds and rough
seas. A Winter Storm Watch is in effect from Friday afternoon
through Saturday afternoon for Shemya and Amchitka. This storm is
projected to impact the entire chain.

&&

.MARINE (Days 3 through 5 Sat through Mon)...

A strong low in the Bering on Saturday will bring widespread gale
force winds across the Bering, Aleutians, and westward to near
Kodiak Island. Storm force winds are expected closer to the low
center, over the western Bering and central/western Aleutians. By
Sunday this system will weaken, with gales confined to the
central/western Aleutians and the western Bering. For the Gulf, on
Sunday and Monday westerly winds will be near gale force.

&&

.LONG TERM FORECAST (Days 4 through 7 Sun through Wed)...

On Sunday there will be a low in the Bering, with a trough
extending northeast into northern Alaska. Southwesterly flow aloft
will be over all of southern Alaska, extending westward through
the eastern and central Aleutians. Through Monday the models are
in fairly good agreement that the Bering low will weaken and
slowly drift south, while the northern Alaska trough drops
southward into southern Alaska. By Tuesday the deterministic
models diverge significantly on where the Bering low goes, and
also on how the upper level pattern develops over Alaska in
general. Therefore for Tuesday and Wednesday ensemble mean
forecasts are preferred, and forecast confidence is somewhat low.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Watch 191
MARINE...Gale Warning 173 174 175 176 177 178 411 413
         Heavy Freezing Spray warning 129 130 185 414

FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PD
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PJS
MARINE/LONG TERM...BL