Small Craft Advisory 822, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
449 PM AKDT Sat Nov 2 2019

.ANALYSIS AND UPPER LEVELS...
A 100-110 kt westerly jet, pinched between the cold upper trough
over the Bering Sea and ridging over the NE Pacific, stretched
from the Alaska Peninsula to across the North Gulf and SE Alaska.
A fairly extensive cloud band, associated with a broad baroclinic
band, extended from the Alaska Peninsula to over the Northern
Gulf. Kodiak Island was receiving some light rain from this band
and Doppler Radar showed precipitation advancing northward in the
Gulf. Abundant low level moisture and shallow surface inversions
lead to widespread low stratus and fog across Southcentral,
especially in the Cook Inlet to Mat-Su corridor (including the
Anchorage Bowl). Low ceiling and some fog was also observed over
Bristol Bay. Generally cloudy conditions and light winds persisted
over the Aleutians. Southeasterly winds however were increasing
over the western Aleutians in advance of and approaching weather
front.

&&

.MODEL DISCUSSION...
Short term consistency between models is good in respect to the
synoptic fields. Stratus and fog development will continue to be
the main challenge, especially for Southcentral.

&&

.AVIATION...
PANC...Fog and stratus presents a significant forecast challenge.
While a lot of guidance indicates improving conditions this
afternoon and evening, observations do not reflect that. There
will be very little change in low level flow or stability until
around 15Z Sunday, so IFR/LIFR conditions will likely persist
until then. There will be a slight increase in northerly flow
during the day Sunday as a weak upper trough sinks southward along
with some marginally colder air. This might be just enough to
improve conditions, though would expect some fog and stratus to
remain in the vicinity of the terminal.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2: Tonight
through Monday)...
Southcentral will spend much of the next 48 hours in between an
area of low pressure and its associated front over the Gulf, and
polar high pressure over interior/northern Alaska. By Monday, the
high will move east into the Yukon, and the low moves west into
Bristol Bay. With this pattern in place, any chances of rain will
remain along the coast and over the Gulf, including Kodiak, Homer,
and Seward by late in the day Sunday.

Tonight, the fog and low stratus that has been stuck over much of
Southcentral today will persist, with only light northerly winds
perhaps moving the fog around, but not doing much to mix it out.
It won't be until later in the day on Sunday when the winds
increase enough with the approach of the Gulf front that there
will be more significant mixing and drying of the atmosphere away
from the coast. Thus, the fog and low stratus should not be as
widespread Sunday night as it is expected to be tonight. The winds
will increase Sunday night and into Monday through Broad, Isabel,
Mentasta, and Thompson Passes and down the Matanuska Valley on
north to northeasterly winds. This will be due to colder air gradually
filtering into the Copper River Basin as the aforementioned polar
high skims past the Basin and into the Yukon. The front along the
coast should weaken considerably through the day Monday as the
parent low shifts westward across the Alaska Peninsula. The
departure and weakening of the low and front should allow clearing
skies to be the common weather trend away from the coast through
the day, so sunshine is likely on Monday in Anchorage and points
north, though in Anchorage it may be filtered sun. Temperatures
area-wide will remain well above average for this time of year
everywhere except possibly the Copper River Basin on Monday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The big question for tonight is whether there will be any fog and
stratus that develops. For the Kuskokwim Delta, it looks like the
drier northerly winds will keep skies mostly clear and keep the
fog away. The Kuskokwim Valley is clearing slowly from the north
while winds increase, so expect mostly clear skies by later this
evening. However, there is potential for fog or stratus to develop
in some of the valley locations. Bristol Bay is more likely to
see the fog and stratus tonight into Sunday morning, but the
mitigating factor once again is the northerly winds. Thus, kept
the forecast at areas of fog instead of more widespread fog with
significantly limited visibility.

The biggest forecast question will be for late Sunday and Monday
morning in the Dillingham area where there may be some freezing
rain. The precipitation chances are increasing and the temperature
is the main question. It does look like temperatures in Dillingham
should warm above freezing by the afternoon so any freezing rain
that does occur should turn to rain by that time. It is also
possible that, despite the northerly winds, temperatures will warm
up fast enough that there is little-to-no freezing rain by the
time the temperature warms above freezing on Monday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The ridge axis over the central Bering Sea will remain largely in
place into Monday and then begin to weaken by Monday night into
Tuesday. This will keep a front approaching the Aleutians from the
west at bay for a while, but the western Aleutians will see the
winds increasing early next week due to the pressure gradient
between the front and ridge. The eastern Bering Sea will be
impacted on Monday into Tuesday by the same front moving through
Southwest mainland Alaska which was mentioned in that section.

&&

.MARINE (Days 3 through 5: Tuesday through Thursday)...
A moderately strong low south of the Alaska Peninsula may produce
gale force winds south of the Alaska Peninsula and Eastern
Aleutians through Tuesday. A strong low will move into the western
Bering Sea Tuesday and storm force winds are possible along and
in advance of its front across the western Aleutians and western
Bering Sea offshore regions Tuesday.

&&

.LONG TERM FORECAST (Days 3 through 7: Tuesday through Saturday)...
The models are in good agreement amplifying the ridge into the
Bering Sea at the surface and aloft Monday through Wednesday. As a
result strong low pressure and a front move into the western
Bering Sea and moderate low pressure remains south of the Alaska
Peninsula. The models then depart from yesterdays solution that
held the low south of the Alaska Peninsula, and now are trending
to a low over or crossing the Alaska Peninsula Wednesday as the
Ridge in the Bering retrogrades west and weakens. With this in
mind, and lacking consistency in the model solutions, we will
trend toward the ensemble solutions that are keeping a low in the
Gulf of Alaska and along or south of the Alaska Peninsula while
maintaining the high pressure over northeast Alaska. Over the
Bering Sea and Aleutians the trend will be to hold weak high
pressure over the west central Bering with moderate to strong lows
in the extreme western Bering Sea and Kamchatka Peninsula.

The models persist with bringing colder conditions to the Copper
River Basin Wednesday, with much colder air moving in Thursday.
Friday and Saturday solutions are hinting at a return to the
warmer air for the Copper River Basin, however, confidence in the
models is low at that time.

&&

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

&&

SYNOPSIS AND MODEL DISCUSSION...BC
SOUTHCENTRAL ALASKA...JW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...EZ
MARINE/LONG TERM...SA