Small Craft Advisory 575, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
355 AM AKDT MON JUL 18 2016

.ANALYSIS AND UPPER LEVELS...
There is a ridge of high pressure aloft extending through the
Eastern Aleutians into the northern Bering, and an upper level
closed high over the Kamchatka Peninsula. The satellite imagery
is showing low stratus/fog under the ridge over the eastern Bering
streaming eastward into the Bristol Bay coastal communities this
morning. While the interior north of the Alaska Range has a
shortwave moving from west to east positioned through the Seward
Peninsula extending into the Eastern Siberian region. The water
vapor imagery is showing a swath of drier conditions extending
from the northern Bering into the Kuskokwim Delta eastward before
crossing the ALaska Peninsula near Iliamna this morning. This
coincides with the ridge building into the area, and is accompanied
by westerly flow resulting in warm temperatures for the Southwest
Alaska region. These warmer temperatures are spreading into the
Southcentral region along with the westerly gap winds. This can
be seen through the Barren Islands with reports of gale force
westerly winds associated with the stronger pressure gradients.
Meanwhile, farther out west there is a closed low near 46N 174E
with an associated trough extending through the Western Aleutians
into the western Bering. This synoptic feature is producing a
swath of stratus/fog through the aforementioned region.

&&

.MODEL DISCUSSION...
The models remain in good agreement this morning as the high
pressure systems dominate the Southwest/Southcentral regions. The
challenge will be the continued areas of fog accompanied by lower
stratus, versus areas of patchy fog in the Bering. Due to the
westerly flow in the eastern Bering, the Southwest Alaska coastal
areas will be influenced by the marine layer stratus/fog this
morning. The preferred models of choice were the NAM/GFS/ECMWF
except for the Gem-Reg due to being slower with the North Pacific
low as it tracks into the Western ALeutians by Tuesday. The
forecast confidence remains above average as we start out the
work week.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
An impressively large and deep upper low in the Arctic Ocean will
slowly drop south over the next couple of days. This will flatten
the upper level ridge situated to the southwest of Southcentral
Alaska. Plenty of high clouds from the baroclinic zone associated
with the Arctic low will push across Southcentral Alaska. Most of
the area will not see any rain through Tuesday night, as heights
remain fairly high and the Alaska Range blocks some of the mid
level moisture needed for precipitation. Northern portions of the
area are the exception, with some chances of rain in the Copper
River Basin and the northern Susitna Valley. At the lower levels
the flow is offshore, and gusty winds will continue at some
locations, especially along the coast.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA...
Ridging sits just to the west of Southwest Alaska and it looks to
last through Tuesday. The ridge is bringing west to northwest
flow over the area that is allowing for some moderation of
afternoon temperatures, but they will still largely remain at or
above normals. This flow may also push in marine fog along coastal
areas in the morning hours. For the most part the ridging will
keep rain out of the area except for a disturbance moving through
the Lower Kuskokwim Valley that will likely bring some rain,
mainly on Tuesday. Tuesday night into Wednesday a front will push
in over Southwest Alaska bringing more widespread rain to the area.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS...
With ridging over the eastern Bering, light southerly flow and
fog cover much of the area. However, a new system is approaching
the area from the North Pacific whose front should make it over
the Western and Central Aleutians this evening. The main low
center will make it to the Western Aleutians Tuesday afternoon
with the front making it to the Pribilof Islands by this same
time. The front will then fracture with the main part pushing east
towards Southwest Alaska and draping back across the Eastern
Aleutians. On Wednesday the majority of the front will have pushed
inland.

&&

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

Wednesday morning, there will be a rather strong arctic trough
centered over the Brooks Range with a closed upper level low over
the western Bering Sea. In between will be shortwave ridging over
the eastern Bering Sea. Offshore flow will keep Southcentral on
the warmer side while westerly flow over Southwest will keep that
region more moderated. Rain will be relegated to the Alaska Range
and parts of the Talkeetna/Wrangell Mountains. This pattern will
persist through Wednesday morning before a front associated with
the Bering low moves into southern Alaska, spreading rain and
clouds eastward through Friday. This will be a moist and cooler
pattern after the hot and dry pattern most of southern Alaska has
seen the past week. By the weekend, uncertainty rises with just
how fast the low moves into the Gulf of Alaska and out of
Southcentral region, but the weekend looks to improve as outflow
winds ensue behind the departing low.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning...130 131 176 177 178.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PD
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...JA