Small Craft Advisory 462, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
500 PM AKDT Tue Jun 12 2018

.ANALYSIS AND UPPER LEVELS...
The Arctic trough that has been over the area the past few days
is moving eastward and exiting the region leaving drier conditions
behind it. Cooler temperatures aloft with warmer temperatures
towards the surface near the ALCAN border are causing a bit of
instability. The upper level wave sitting over Southcentral is our
main weather driver causing some showers to still develop across
the north Gulf coast this afternoon and will continue through the
evening.

A ridge over eastern Russia and the Bering continues to bring high
pressure dominating the area with dry, northerly flow. A small
shortwave over the Y-K Delta earlier today that brought a few,
now diminishing, showers is dropping down towards Bristol Bay
increasing mid-level cloudiness.

&&

.MODEL DISCUSSION...
Models are in good synoptic agreement with major features and
timing of upper level waves. There is much better agreement today
between placement and intensity of the North Pacific low moving
towards the central and eastern Aleutians on Thursday. The NAM is
the preferred model for the forecast period due to its decent run
to run consistency.

&&

.AVIATION...
PANC...VFR conditions will persist. Gusty south-to-southeast
winds will taper off by midnight this evening. The shifting
pressure gradient should allow an Inlet Breeze to develop
tomorrow.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Scattered showers will develop this evening as low pressure sends
short waves from the Alaska Range to the Gulf. Isolated
thunderstorms will be confined east of Glennallen along a thermal
ridge axis that extends across the southern Alcan border. Showers
are expected to diminish across the region after peak heating,
however scattered activity will continue across the Copper River
Basin as weak troughing lingers along the eastern Alaska Range.

A short wave ridge building from the southwest Gulf will bring
sunny skies across much of the region on Wednesday. The next front
organizes over the North Pacific Wednesday night and swings a
boundary to the southern Gulf late Thursday. This front paces
quickly to the southern mainland spreading rain across the Kenai
Peninsula Friday morning then inland by midday Friday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The region remains situated between high pressure anchored over
eastern Russia and an upper-level trough slowly digging southeast
toward the Alaska Panhandle. This has set up a northerly flow,
bringing dry and stable air to much of the interior of Southwest
Alaska. Farther south, a weak shortwave sliding south of Cape
Newenham this evening will enhance the areal coverage of low
stratus and patchy fog overnight for locations along the northern
coast of the AKPen. A second shortwave breaking off of the
unseasonably strong 500 mb low positioned over the Arctic coast
will dive south late Wednesday into Thursday. This system will not
progress as far south as the system early Monday, but will
instead slide east after clipping the YK Delta and northern
forecast zones. A weak surface front will push south of Bethel,
however, bringing a reinforcing short of drier air and gusty
northerly winds for the second half of Thursday.

Also on Thursday, an occluded front associated with a strengthening
low in the north Pacific will move north along the eastern
Aleutians and AKPen bringing increased cloud cover and rain to
the region late Thursday through Friday. Gusty easterly winds are
also possible beginning late Thursday night, especially in gap
locations east of the Alaska Range, in advance of the front.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Low stratus and patchy fog will continue through Wednesday across
much of the Aleutian chain as high pressure and a persistent
northerly flow remain the dominant weather features over the
Bering. By Thursday, a developing low will advance toward the
eastern Aleutians. This system will quickly strengthen as it heads
north with an occluded front moving over the eastern Aleutians
and AKPen Thursday. Gale-force winds and seas as high as 18 feet
along the Pacific side of the central and eastern Aleutians are
also expected on Thursday as the low tracks north.

&&

.LONG TERM FORECAST (Days 3 through 7..Fri through Tue)...
Besides some convection and a strong Arctic trough over last
weekend, June has started out very Summer-like across much of
Southern AK. But things are about to take a turn to a much
cloudier, rainy, and slightly cooler set-up. The well-advertised
front will make its way into AK from the North Pacific on Fri.
This front will have pack a little extra "punch" as it wraps in
some extra-tropical remnants of a former tropical storm. So expect
very wet conditions along the Gulf Coast late Fri and continuing
into Sat. It will also bring a healthy amount of QPF to SW AK as
the front slings through there. Places in the lee of the Kenai and
Chugach Mountains will see somewhat reduced precipitation values
with some downsloping, but they will also see some impressive
channeled winds. From the Barren Islands, to the Turnagain Arm,
the Knik River Valley, and the Copper River Basin, gusty
southeasterly winds are in store.

This system will reorient the entire longwave pattern. A broad
trough will become well established over the Eastern Bering. This
sets the entire southern portion of the state up with moist,
southerly flow. While this certainly doesn't mean continuous rain
for the area, it will spell a marked increase in cloud cover.
Then, as waves of energy pinwheel through the base of the trough
and move south to north towards southern AK, each will have the
potential to bring steady rain. This will be especially true for
the Gulf Coast (Prince William Sound, Cordova, etc.). This pattern
really looks to hold on through much of next week (June 18-22).
Overall, fire weather concerns will be relatively low during this
time.

&&

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

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
LONG TERM...MSO