Small Craft Advisory 548, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
920 AM AKDT Tue Jul 30 2019

.ANALYSIS AND UPPER LEVELS...

There is an upper low near southeast Alaska with remnant moisture
producing isolated showers in the vicinity of Cordova and
Montague Island. There is a ridge axis extending from the north
Pacific into southwest Alaska. There are a few shortwaves riding
over the ridge axis. There is a second upper low near Shemya that
supports a frontal boundary at the surface. There is a jet core
pushing through the Aleutian Islands and another jet core over the
northern Bering.

&&

.MODEL DISCUSSION...

There has been a shift toward a more rainy pattern for
Southcentral Thursday with a digging upper trough. Synoptically,
models remain in good agreement through the short term.

&&

.AVIATION...

PANC...VFR conditions and light winds are expected through the
TAF period. Shallow ground fog formed yesterday morning near PANC.
Its possible that shallow ground fog will develop again this
morning and the situation is being actively monitored. Current
thinking is that the fog will not impact the tarmac at PANC.

&&

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

Upper level ridging is building into Southcentral today and will
bring in some overall warmer temperatures and sunnier skies
through tomorrow. The exception today will be the Copper River
Basin which will see some continued shower activity this afternoon
and evening with a chance for an isolated thunderstorm as well.

Wednesday night into Thursday will bring in a brief change to the
weather as a front associated with an Arctic trough in northern
Alaska will move through the Susitna Valley and then the Copper
River Basin. At this time a low undercutting the Gulf of Alaska
will push some moisture into the Gulf coast region and bring a
quick shot of some rain.

&&

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

High pressure currently over southwest Alaska will continue the
warming and drying trend through midweek. This high will also keep
weather quiet over the area. Wednesday the weak low that is currently
in the Bering will reach the southwest coast, bringing cloudy
conditions and showers with it. The low will be short lived as
zonal flow will quickly bring in a short wave ridge on Thursday.

&&

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

Low pressure is currently moving through the Bering Sea as
expected. It is producing showery precipitation as it goes. Behind
the low is a shortwave ridge that will last for about a day as it
progresses east. As high pressure goes over the Bering, low level
stratus and fog already present can be anticipated to hold in
place. Later in the week a more substantial low pressure system
with gale force winds will enter the Bering Sea.

&&

.MARINE (Days 3 through 5/Thursday through Saturday)...

Confidence is high that a strong storm will push a front into the
western Aleutians late Wednesday. Along and ahead of this front
gale force winds are likely starting near the western Aleutians
Wednesday and spreading to the Yukon-Kuskokwim Delta coast late
Friday.

&&

.LONG TERM FORECAST (Days 4 through 7/Friday through Monday)...

We start the long term period with a large low over the northwest
Bering Sea with a front draped across the eastern Bering Sea
through the eastern Aleutians. Model agreement is good with
bringing this low north to the Arctic through Sunday as weak high
pressure builds in over the southern mainland from the Gulf of
Alaska. As this system vacates the Bering Sea, weak low pressure
slides into the western and northwestern Bering Sea Monday. Weak
low pressure also moves into the eastern Aleutians. The models
vary on the placement and intensity of these lows, though they are
consistent with them being on the weak side.

In the upper level, a ridge over the central Bering Sea amplifies
from the north Pacific into the southwest mainland Friday, then
rapidly slides east as another upper level low and trough move
into the northern to central Bering Sea Saturday. That low and
trough move into the Arctic as the ridge flattens Sunday. For the
southern mainland this pattern is conducive to warmer drier
weather through Saturday. Southwest Alaska, the Bering Sea and
Aleutians can expect periods of windier and wetter weather.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

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