Small Craft Advisory 802, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
446 AM AKDT Sun Oct 27 2019

.ANALYSIS AND UPPER LEVELS...
A highly amplified pattern continues, as a full latitude trough
dominates the western half of the Bering, with a 980 mb low
positioned south of Nikolski, which is the remnants of a former
typhoon. Further east, a ridge extended into the Copper Basin
from the eastern Gulf. In between these systems, a deep tropical
connection, down to near 20N, continues. A couple of disturbances
embedded in the flow are helping fuel "enhanced" surges of this
moisture.

&&

.MODEL DISCUSSION...
Overall, the models remain in good agreement through the middle
of next week. However, there are a few smaller scale differences,
mainly with regard to the areas of surface low pressure riding
northward in the flow. This has played a role with the strength
of the winds affecting southwest Alaska. It also affects how far
into Anchorage does the Turnagain winds make it, as some of the
latest hi-res models show northwest to northeast winds under 15
mph being prevalent, while others bring in southeast winds of 30
to 40 mph. In either case, the models have struggled in
consistency with the strength of the surface winds.

&&

.AVIATION...
PANC...Winds remain a challenge through the forecast period, as
this morning's analysis shows a stationary surface trough roughly 5SM
southeast of the field. LLWS will continue to be an issue within
2000 feet AGL, with an added concern being wind variability in
direction as the surface feature to our southeast influences the
wind fields from time to time.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2/Today
through Monday night)...
The overall forecast for the next couple days remains on track
with widespread wind and rain across much of the western Gulf
and Southcentral. The biggest forecast challenge is winds in
the Anchorage area, particularly along the Anchorage hillside.
Pressure gradients support "down Inlet flow" for much of today and
tonight, meaning the Turnagain Arm jet will bend southward as it
exits Turnagain Arm. Under this scenario winds along the upper
hillside will generally be lighter than Turnagain Arm. However, a
surface wave tracking up the cold front along the Southwest Alaska
coast this afternoon/evening will weaken the down Inlet flow and
lead to strengthening winds along Turnagain Arm and the upper
hillside. The surface wave is pretty far west, but could see some
warning level gusts on the hillside. Some guidance shows some of
these winds spreading into other parts of Anchorage. However, with
some down Inlet flow remaining, think the lee side trough and
northwest flow will persist across the lower elevations of
Anchorage. Winds will then diminish overnight before peaking again
as the cold front passes through Monday morning. At this point in
time pressure gradients will support gusty east to southeast winds
moving across much of Anchorage. This also seems like the most
likely time to reach high wind levels (75 mph or higher) along the
Anchorage hillside. Bottom line, the High Wind Warning has been
extended through midday Monday and there will be fluctuations in
the winds through then.

After the cold front pushes onshore and weakens during the day
Monday, winds will diminish some, but gusty south to southeast
winds will persist across much of the region. As the Bering Sea
trough shifts eastward, a series of upper level short-waves will
rotate through Southcentral. With more uniform southerly flow,
expect wet conditions for most of the region. The one notable
exception will be the heart of the Copper River basin, which will
likely remain dry for this entire event.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1-3: Sun-Tue)...

Strong winds will continue over Southwest Alaska this morning,
especially out of Kamishak gap and along the coastal areas,
before beginning to taper down by this evening as the pressure
gradient weakens across the region. A fast moving surface wave
will move up along the Southwest coast near Hooper Bay by this
afternoon before continuing northward, which will bring a quick
round of heavier precipitation. This wave will also bring gale
force winds to Bristol Bay, which will weaken to small crafts by
this afternoon. Areas south of the AKPEN will see a brief period
of storm force winds this morning, which will diminish after noon
as the surface wave moves out of the area. Gap areas will also
likely see stronger gusts during this period.

A showery pattern will continue across the rest of the area
through the evening hours. Another wave will move northward from
the AKPEN overnight into Monday morning, which will bring a second
round of heavier precipitation across the Bristol Bay region.
However, the exact placement is still a bit uncertain with this
feature. Southwest can expect to stay under a showery pattern
through Tuesday afternoon, with any new precipitation likely to
fall as rain. By late Tuesday, cooler temperatures will move into
the Kuskokwim Valley as arctic air moves in. This should be about
the same time that precipitation is diminishing over the area, but
there could be possible snow for a brief period before the
precipitation ends.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

Gale force winds over the western Bering on the backside of a low,
centered east of Adak, will weaken to small craft by Monday
morning as they move into the central Bering. Widespread rain will
accompany this low system. Weak winds and cyclonic flow
positioned west of the Pribilofs this morning will continue to
move into the eastern Bering through Tuesday morning.

&&

.MARINE (Days 3 through 5: Tuesday through Thursday)...

A North Pacific low approaching the south side of the Alaska
Peninsula Wednesday morning will produce gales in that area from
Wednesday into Thursday morning over the Gulf. A potential barrier
jet Thursday morning may also briefly produce gale force winds
Thursday morning. Elsewhere, gales are not expected through
Thursday in the Bering/Aleutians.

&&

.LONG TERM FORECAST (Days 3 through 7: Tuesday through Saturday)...

A surface trough of low pressure centered off the coast of the
Kuskokwim Delta will move inland Tuesday. Widespread shower
activity is expected out ahead of this feature, in both Southwest
and Southcentral. The approach of the low, despite its weakening,
will keep Turnagain Arm and Upper Hillside winds gusty through the
day, though without much else to speed up the winds, strong winds
are not expected.

The next North Pacific low will approach the Alaska Peninsula
early Wednesday morning. The low is expected to track northeast,
as associated rain tracks well ahead of the center of the low,
thanks in part to the remnants of the low that moves into Southern
Mainland Alaska. The low center tracks up Shelikof Strait on
Thursday, and becomes a diffuse area of low pressure over
Southcentral by Friday. Along this track, warm, wet, and windy
weather is likely to continue in Southcentral potentially into
Friday. As is typical for the long-term forecast, the details of
all of this are highly uncertain and will be refined in future
forecasts.

Despite the uncertainty in the details, the models are in decent
agreement that behind this low there will be a significant
pattern shift in the late Friday or Friday night period. The shift
will consist of significantly colder and drier weather with strong
outflow winds across Southern Alaska as an area of high pressure
builds in through the weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 101, Flood Advisory 125, Winter Weather Advisory 145
MARINE...Storm Warning 130 131 132
         Gale Warning 119 120 125 136 137 138 139 141 150 160 176 177 178 185 351
                      352 411 412 413
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PD
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...JW