Small Craft Advisory 472, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
429 PM AKDT Mon Jun 24 2019

.ANALYSIS AND UPPER LEVELS...
An upper level ridge remains over the Eastern half of the domain
while a weak front is approaching the Pacific side of the Eastern
Aleutians/Alaska Peninsula. Dense fog and low stratus held on
through much of the morning hours across SW AK. However, it is
finally starting to abate as full June sunshine works on it from
above. There are plenty of lows clouds and some light rain over
much of the Aleutians and Bering Sea courtesy of weak low pressure
continuing to fall apart out there. The Kenai radar is starting to
pick up some returns from thunderstorms that have already formed
in the Copper River Basin and some showers over the Susitna
Valley.

Most of the upper-level (30,000') jet activity remains well away
from the mainland. The most coherent portion of jet support is
just south of the Western Aleutians and runs from west to east at
105 kt. Otherwise, only a weak fingers of 65-70 kt are flowing up
and over the ridge centered over Bristol Bay.

&&

.MODEL DISCUSSION...
Models remain in very good agreement lending to high forecast
confidence through most of the week. The specific areas of concern
would be how strong the southwest winds off the Cook Inlet become
tonight and how far inland they can push. Other fine-scale details
that remain challenging to pin down would be if any fog/marine
stratus were to redevelop tonight.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. Smoke will
increase through the overnight hours with southwest flow.
Uncertainty is fairly high with how much it might reduce
visibility at the terminal Tue morning.

&&

.FIRE WEATHER...Swan Lake Fire...Western Kenai Peninsula:
The pattern will continue to support warm temperatures, plenty of
sunshine, and an outside chance for thunderstorms for the next 2
days. The biggest concern for tonight remains a potent push of
southwest winds off the Cook Inlet. A weak trough sliding up from
Kodiak Island should help to ferry these stronger winds inland
over the entire fire through the evening. Much like Sunday, this
could aid in some convective development. It should also usher in
some higher RH values with some marine influence. Into Tue, a
stronger ridge of high pressure will being to build in. This will
once again make the wind forecast very challenging as local
influences will take over. Subsidence will increase with this
ridge of high pressure leading to warming (even hot) temperatures
and less chance for any thunderstorms (even over the mountains) by
late Tue.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through
3/Tonight through Thursday)...
The hot and mostly dry weather pattern will continue. A ridge of
high pressure overhead will shift eastward tonight and Tuesday as
a weak upper level short- wave moves through. This may produce a
few more clouds on Tuesday. Showers and thunderstorms will be
confined primarily to interior Southcentral, from the Susitna
Valley eastward across the Copper River Basin.

An even stronger ridge will build into Southcentral from the west
Wednesday through Thursday. The combination of strong subsidence
underneath the ridge combined with offshore low level flow will
lead to hot and dry conditions for all of Southcentral, including
along the coast. The flow will be strong enough to keep sea
breezes at bay until later in the day. This will allow
temperatures for Seward, Whittier, and Valdez to keep rising
through the afternoon hours. The hottest day in the next few will
be Thursday, with even hotter temperatures possible as we head to
Friday and Saturday. Daytime highs will likely approach and
possibly exceed record levels in some locations.

One specific concern in Southcentral is the track of smoke from
the Swan Lake Fire on the western Kenai Peninsula. Strengthening
southwesterly flow is bringing more of the smoke northward to
Anchorage and the Matanuska Valley today. As the atmosphere
stabilizes overnight into early Tuesday morning the smoke will be
trapped closer to the surface. Thus, will likely see deteriorating
visibilities and a more noticeable smell of smoke. Winds higher
up will also carry some smoke eastward from the fire across the
eastern Kenai Peninsula. The overall wind pattern will remain the
same until Tuesday night into Wednesday when flow should shift
back to coming out of a northerly direction. This will lead to
improvement in Anchorage and the Mat Valley, while areas south and
east of the Swan Lake Fire will see an increase in smoke.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Wednesday Night)...

The weak ridge along the Bering Sea coast will be nudged east in
response to the Bering Sea low and advancement of its front toward
the Bering Sea coast. This will result in more mixing of the
lower atmosphere and thus mitigate and reduce the extent of the
fog over the Bristol Bay region, although the low level stratus
will remain over the region. The push of more stable air across
southwest Alaska will remove any threat of significant
thunderstorm activity over the southwest mainland the next several
days.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: Today
through Wednesday Night)...

The big picture for the Bering Sea is the low now over the central
Bering Sea and it's associated front. This vertically stacked low
will slowly drift north then west through Wednesday. Along the
front a low forming over the eastern Aleutians will move north
and the frontal boundary will persist along 170W. This will hold
the stronger, though sub gale force wind, over the eastern Bering
Sea through Wednesday. There is widespread low stratus and fog
over the entire Bering Sea.

&&

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

...Bering Sea and Aleutian Coastal Waters...

A weakening front will stretch across the eastern Bering through
the Alaska Peninsula, with small craft criteria winds
accompanying it. These winds drop below this criteria for Friday
and Saturday, as high pressure builds in.

Further west, an area of low pressure centered well west of Shemya
on Thursday, will reach southern Siberia by Saturday morning. Its
associated front will bring little fan fare to the western Bering
and Aleutians, with periods of rain being the main impact from
this system.

...Gulf of Alaska...

High pressure will remain in control through the period, slowly
weakening by Saturday. This will keep the region dry with winds
remaining below headline criteria.

&&

.LONG TERM FORECAST (Days 3 through 7)...
(Thursday through next Monday)

The forecast is starting to get somewhat more clear for the
weekend into the start of next week. What does look to remain in
place is very warm temperatures for much of the southwest
mainland into southcentral, with some interior showers of
thunderstorms possible for the southcentral interior locations
beginning again this weekend. Things are still pretty murky
though for Sunday and Monday as the general trend is for a pattern
shift, breaking down the ridge of high pressure over these areas
while going to a more zonal flow. This would allow some
disturbances to cross these regions with increasing rainfall
potential at times. However, how quickly this occurs is still in
debate as the ECMWF model breaks the ridge down much quicker than
the GFS, with the Canadian much closer to the GFS. Thus, prefer a
longer period of dry and warm conditions continuing with the
general premise that a change will occur sometimes towards early,
or more so the middle, of next week.

Further west across the Bering and Aleutians, areas of showers
across the eastern Bering and Alaska Peninsula through Friday
morning along a weakening front, before a short wave ridge of high
pressure builds in, bringing drier conditions to this area.
Another area of showers along an approaching front are expected for
the western Bering and Aleutians during this period.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Advisory 145.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MSO
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SA
MARINE/LONG TERM...PD