Small Craft Advisory 434, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
445 AM AKDT Thu May 31 2018

.ANALYSIS AND UPPER LEVELS...

The longwave pattern features a broad area of troughing that spans
from the Eastern Bering across Southwest Alaska and into the Gulf
Of Alaska. The remnants of a surface low circulation are
southeast of Kodiak. Currently, there is a ridge over the Western
Aleutians. The latest satellite imagery has a widespread area of
low level and mid level clouds from the Alaska Peninsula to
Cordova. The four radars monitoring the area of responsibility
all have something on them. The Kenai radar just has isolated
showers, but the radar at Bethel and Middleton Island are much
more active.

&&

.MODEL DISCUSSION...

Models are in good consensus through Sunday with the major
synoptic features. The NAM GFS and ECMWF have converged one the
solution that brings the new low which is currently east of Japan
towards the Western Aleutians. Then moves the low north of the
chain and into the Western/Central Bering. The global models are
in sync with both the intensity and timing. The NCEP RMOP/Relative
Measure Of Predictability for the Western Aleutian low is handily
in high confidence territory. For the low south of Kodiak the
models steer it into the Gulf of Alaska and slowly pushing
southeastward.

&&

.AVIATION...
PANC...VFR conditions expected this forecast period. The radar for
Kenai (PAHG) has detected s few showers over the Cook Inlet. Added
VCSH to the TAF to account for the possibility of them approaching
the aerodrome.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
Most areas will begin to see a gradual clearing trend today as the
Gulf low slowly exists the area and weakens. This will will allow
for warmer and drier conditions from the interior and Yukon
Territory to move into the area, along with a strengthening
thermal trough that will be the focus for convection into this
weekend. After breaks in the clouds form over much of
Southcentral later this morning, expect diurnal shower development
over most areas north of the Kenai with isolated thunderstorms
over the Copper River Basin. The thermal trough will then begin to
intensify on Friday and Saturday, allowing for more widespread
thunderstorm development around the Copper River Basin and Susitna
Valley, as well as the potential for isolated thunderstorms from
Eagle River area into the Matanuska Valley on Friday and possibly
Saturday. Otherwise this pattern will allow for more seasonable
temperature with sea breezes expected along the usual areas along
Cook Inlet and the North Gulf Coast into this weekend.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Cyclonic flow on the eastern periphery of the weakening Bering low
will continue to support cool and showery conditions today across
the southwest mainland. Extensive cloud cover and onshore flow
will generally limit thunderstorm potential this afternoon,
although a few isolated strikes will be possible in the Lower
Kuskokwim Valley if the area can get a few breaks of sunshine to
help destabilize the atmosphere. Diurnal convective activity
should be more prevalent across the region by Friday and
continuing into Saturday as the pattern transitions to a warmer
offshore flow regime and the thermal trough is reestablished from
the Kuskokwim Valley into Greater Bristol Bay. This will yield
more widespread thunderstorm potential over the course of the next
few afternoons/evenings.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A relatively quiet pattern will continue through Friday morning as
the weakening low supports scattered to numerous showers across
the eastern half of the Bering while transient ridging promotes
even more benign conditions out west. Attention then turns to an
unseasonably strong low poised top enter the western Bering on
Friday. The associated front should be strong enough to produce
a narrow swath of storm force winds as it enters the Western
Aleutians, with more widespread storms then developing Friday
night into Saturday in cold advection on the back side of the
system. The front will track east across the Bering through
Saturday afternoon, bringing a quick shot of heavier rain to much
of the chain before weakening rapidly by the time it reaches the
Akpen late Saturday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Models have come into somewhat better agreement with regards to
the progression of the upper level pattern this weekend through
early next week. The deep, vertically stacked Bering low will
gradually fill as it meanders around the western Bering through
the weekend. The weakening associated frontal system will reach
the eastern Bering and Alaska Peninsula Saturday night and then
stall out and shear apart along the Southwest Alaska coast on
Sunday. A frontal wave will develop along a trailing section of
the front south of the Alaska Peninsula Sunday night but will
track off to the east well south of the Gulf Monday and Tuesday.

The broad upper level low over the Bering will progress gradually
east to be centered over central Bering Monday with a trough
elongating east Tuesday to stretch across the Alaska Peninsula
and into the western Gulf. The entire pattern will then continue
to shift to the south and east with upper level low centered over
the Alaska Peninsula and western Gulf Wednesday through Friday.
Of the all the various model solutions from yesterday's runs, this
one will bring the coolest overall weather. Easterly flow to the
north of the low will bring persistently showery weather to
Southwest Alaska while troughs and fronts rotating through the
Gulf will bring rain to the Gulf coast and cool, generally cloudy
onshore flow further inland to Southcentral Alaska.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...GALE 413 411 175 176. STORM 177 178.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...DEK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
LONG TERM...JR