Small Craft Advisory 527, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
447 PM AKDT Sat Jul 7 2018

.ANALYSIS AND UPPER LEVELS...
Low pressure continues to dominate the Bering Sea/Aleutians as
low pressure and a strong front advance eastward. Satellite
imagery shows a swath of dense marine stratus along the front,
which is encompassing most of the Bering Sea and Aleutians. The
upper-level low continues to deepen which is being supported by a
140 kt jet stream at 300 mb. Near the surface, a trough extends
from the low over the eastern Bering. The front is producing light
rain and fog along the western coast of mainland Alaska and AK
Pen. Overnight, fog extended into the southwest mainland reaching
Bethel, Dillingham and Koliganek. Sunny skies, and warm
temperatures are still the trend across Southcentral Alaska as
high pressure persists in the Gulf of Alaska. Gusts have started
to pick up along the North Gulf Coast signifying the beginning of
the end of the sunny summer-like conditions that have been
experienced for the last week. An increased pressure gradient
along the coastline is creating gusts through Turnagain Arm and
into Anchorage. Under the ridge, widespread stratus has taken hold
covering most of the Gulf. Fog and light rain are also inching
into Prince William Sound and coastal areas around the Gulf.

&&

.MODEL DISCUSSION...
Model agreement remains very good into early next week with the
very slowly moving Bering low as it begins to dominate the weather
over the mainland. As a result forecast confidence remains good
into Monday, with few significant changes needed to what was
already in the forecast today. The biggest model disagreement in
the forecast period doesn't really appear until the middle of next
week as differences begin to arise in the handling of energy
rotating around the Bering low from Russia, which is hampering
forecast confidence at the moment beyond Tuesday.

&&

.AVIATION...
PANC...Gusty southeasterly winds continue increasing this afternoon
into early this evening as the pressure gradient along the
Chugach continues to tighten. These winds may drop off a bit
during the overnight hours, however they will increase again
Sunday morning as a frontal system moves through the Gulf. These
winds will continue to bring areas of LLWS for any approaches from
the west. Ceilings may briefly drop below 6000 ft with a period of
rain midday Sunday, but expect prevailing conditions to remain
6000 ft or higher.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The latest satellite image continues to show mostly clear skies
across the Anchorage Metro Area and the northern portion of the
Cook Inlet. The leading edge of the cloud shield associated with
the next frontal boundary is already at King Salmon. There is
already a healthy amount of stratus over Prince William Sound and
the Gulf Of Alaska. Expect an increase of southerly winds and
onshore flow as a low enters the region from the west. The pattern
will change tonight and Sunday as the Bering front moves into the
Gulf. This storm will put the kibosh on the blue skies. The
pressure gradient will increase and there will be an uptick in
winds. Expecting southeast winds for Anchorage. There is a very
good chance that Anchorage will see rain tomorrow but its not a
slam dunk. Generally speaking, increasing chances of rain are
expected for inland areas, while steady rain will develop along
the coast.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A pattern shift is well underway as an occluded front marches
into the southwest mainland. As of late this afternoon, the cloud
shield stretches from Aniak down to King Salmon with precipitation
falling east of Bethel south into Bristol Bay. Rainfall will
advance into the interior tonight as the front moves to the
northeast. Behind the front, a rainy and cool, fall-like weather
pattern takes hold across the region as a series of shortwaves
swings around a low tracking east across the Bering. A persistent
west to southwest flow will advect plenty of moisture into the
region and colder air advecting in aloft with each passing
shortwave will provide the instability to fuel widespread showers
through Monday. The low will track inland by Monday evening. As
it does, the onshore flow will slacken and showers will begin to
diminish, especially along the west coast. One more short-wave
does dive through the central Bering and across the eastern
Aleutians late Monday. This will enhance the northwesterly flow
keeping clouds and showers going over the AKpen through Tuesday.

High surf and minor storm surge are still a concern along the
southwest beginning Sunday, especially in Kuskokwim and Bristol
Bays. A special weather statement is still in effect to highlight
these hazards.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The well-advertised low will continue its trek across the Bering
through the weekend. This will leave just about the entire Bering
under NW to SW flow. Several gale warnings are in effect through
the weekend. Widespread showers will develop tonight over the
Central and Eastern Bering as some colder air wraps into the
system. Several pieces of energy will then rotate from the north
into the back (west) side of the low Sun into Mon. These will only
serve to reinforce abundant showers and near gale-force winds as
some cold air advection increases instability. Well behind this
system, over both the western Bering and Western Aleutians,
widespread areas of fog and low stratus are expected through early
next week as warmer air from eastern Russia advects over the
cooler ocean waters producing a stable marine layer.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long term forecast periods begins Tuesday evening with a deep
upper level low over the state of Alaska. This low will be rather
impressive from an anomaly standpoint with 500 hpa heights around
-2 to -2.5 sigmas. This low will be in the process of weakening
 with a continued moist onshore flow supporting clouds and
 rain/shower threats through Wednesday.

The global numerical models diverge thereafter with quite a bit of
noise muddling the Thu-Sat timeframe as arctic upper level energy
drops through the Bering and phases with a migratory cutoff low
over the North Pac. All models show an eventual phasing, but
differ greatly on timing. The net result is there probably will
be a brief break in the wet/cloudy weather sometime late Wed into
Thursday, but eventually the trough will simply replace the
weakening low and bring more rain and clouds to Southern Alaska
by Friday and into the weekend. Long story short, expect a
typical mid-summer pattern for Southern Alaska consisting of
mostly clouds and chances for rain along with seasonal
temperatures.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...None.

&&

SYNOPSIS AND MODEL DISCUSSION...RA/DEK
SOUTHCENTRAL ALASKA...PS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
LONG TERM...JA