Small Craft Advisory 540, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
919 AM AKDT Thu Jul 25 2019

.ANALYSIS AND UPPER LEVELS...

A mature frontal boundary is pushing across the Bering and into
western Alaska. This system has potent shortwave energy associated
with it. There is an upper level low south of the Gulf of Alaska
with embedded impulses moving across portions of southcentral this
morning.

&&

.MODEL DISCUSSION...

There is good run to run continuity with the models in the short
term forecast period. The global models are in agreement with the
longwave pattern through the weekend.

&&

.AVIATION...

PANC...Anticipating IFR to MVFR ceilings this morning. Conditions
will steadily improve. Winds will be light this TAF period.

&&

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

An upper level trough rotating around the north side of an upper
low centered to the west of the Southeast Alaska Panhandle will
rotate very slowly east today over the eastern Copper River Basin.
As the upper low in the eastern Gulf tracks southeastward
tonight, the upper trough will become a cut off low and remain
centered over the eastern Copper River Basin through Friday. The
associated easterly wave at the surface will produce abundant
rainfall today and tonight before gradually tapering off to
showers on Friday.

A surface front pushing in from the west will reach Kodiak Island
early Friday morning and then continue north over the southern
half of the Kenai Peninsula through Friday afternoon. A secondary
trough will swing into the southwest Gulf Friday and then track to
the northeast, offshore of Kodiak Island Friday night as it
develops into a triple point low. The associated surface front
will rotate through the central Gulf Saturday to reach the
northern Gulf Saturday afternoon and evening while the surface low
continues to the northeast to become centered south of Seward.
This frontal system will bring rainy conditions to the Gulf
Coastal areas while southeasterly winds keep the typical
downsloping areas somewhat drier.

&&

.FIRE WEATHER...

The slow moving easterly wave over the eastern Copper River Basin
will bring abundant rainfall amounts (likely between 1 and 2
inches of rain) to that area today and tonight before turning over
to showers Friday. Elsewhere conditions will continue to be
seasonably cool and mostly cloudy with chances for light rain or
showers. Rainfall will increase over Kodiak Island Friday morning,
the southern and eastern Kenai Peninsula Friday afternoon and the
remainder of the Gulf Coastal areas Friday night through
Saturday. No fire weather concerns are expected in Southcentral
Alaska through the weekend.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1-3: Today through
Saturday night)...

Rain will continue to spread east today as a warm front lifts
across the Kuskokwim Delta this morning followed by a trailing
cold front later today. Lingering moisture within the Kuskokwim
Valley, a result of the light rain produced by the decaying
deformation zone across the interior Southwest yesterday, has
produced some patchy fog overnight. This will scour out later this
morning as the rain shifts east. Southerly winds ahead of this
system will also be on the increase today and become quite gusty
at times. Winds up to 35 mph are already occurring along the
coast this morning from Cape Newenham to Hooper Bay. These
stronger wind gusts should make it as far inland as Bethel.

Behind the front, an unstable, showery regime will set up Friday
and Saturday as the upper-level trough becomes negatively tilted
and slides southeast over the region. Areas around Bristol Bay and
the northern half of the AKPEN could see a round of heavier
showers Friday afternoon as a vorticity maximum coinciding with
slightly cooler air advecting in aloft helps to further
destabilize the atmosphere. The shower activity will decrease
through the day on Saturday as the trough slowly departs and a
weak ridge builds over Bristol Bay. A second trough over the
northern Bering may bring another round of showers to the
Kuskokwim Delta by late Saturday into Sunday, but forecast
confidence is low given model spread in position and strength of
the trough.

Fire concerns will be less than in previous days as a frontal
system brings widespread rain to the area today. Smoke from the
fires may become a concern again for areas near Aniak, Sleetmute,
and Red Devil by early Saturday as a gusty southerly wind
transitions to a light northerly wind. However, lingering cloud
cover, cooler temperatures and scattered showers should all help
to limit fire activity.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1-3: Today
through Saturday night)...

Southerly small-craft winds and areas of rain will continue into
the evening hours across the eastern Bering as a frontal system
moves east over the Southwest coast today. Gusty southerly winds
will also work through gap locations along the eastern Aleutian
Chain and southern AKPEN through this evening as the front tracks
east. A series of troughs moving across the Bering will produce an
area of westerly small-craft winds over the western Bering on
Friday and Saturday along with areas of showers for the central
Bering and Pribilofs.

&&

.MARINE (Days 3 through 5)...

Bering/Aleutians: Benign winds and seas expected. Brief ridging
will build over the Bering, between a trough centered over the
eastern Bering/Aleutians and a Kamchatka low. Winds will be
westerly in general, and while somewhat enhanced near the
inflection between the ridge and eastern Bering trough, will stay
well below gale force. A transition to southerly flow will begin
over the western Aleutians Monday as the Kamchatka low approaches.

Gulf of Alaska: A front will pass over the Gulf from west to east Saturday,
and winds will transition from southerly ahead of the front to
westerly behind. Expect broad cyclonic flow Sunday and Monday,
with winds and seas most likely below advisory level.

&&

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

Southcentral: A wet, active pattern will continue through early
next week. General low pressure in the Gulf will bring
precipitation to the northern Gulf coast through early next week.
How far precipitation propagates inland is a bit uncertain...
though model agreement has improved on the synoptic setup over the
past few runs, there's still enough uncertainty that smaller
scale features are difficult to resolve. Regardless, expect
relatively cooler, cloudier conditions through early next week.
Brief ridging will set up in the middle of the week, bringing
warmer and drier conditions to Southcentral.

Southwest/Bering/Aleutians: A low in the eastern Bering will shift
inland continuing wet, active weather for Southwest through Sunday
or Monday. A ridge will build over the central Bering early next
week, suppressing mixing and likely helping fog form over the
water and coastal areas of Southwest. Meanwhile, a low will
approach the western Aleutians from the Kamchatka Peninsula and
bring a return to wet, active conditions over the Aleutians by mid
next week, then progress eastward through the end of the week.

&&

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

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...JR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
MARINE/LONG TERM...AP