Gale Warning 299, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
416 PM AKDT Mon Apr 8 2019

.ANALYSIS AND UPPER LEVELS...

A vertically stacked low is positioned over the central Aleutians
this afternoon, extending a trough south into the North Pacific. A
shortwave is present within the flow around this trough just
south of Cold Bay. An inverted trough is easterly oriented,
stretched from Bristol Bay over the Gulf of Alaska. South-southeasterly
flow over southern Alaska is bringing moisture and warmer air to
the southwestern mainland and Southcentral. At the surface,
conditions remain mild. A weakening front over the southwestern
mainland is bringing rain showers to the Kuskokwim Delta and
Bristol Bay which can be seen by radar. A surface mesoscale low is
spinning in the northern Gulf which is creating convective style
showers through the coastal waters and northern Gulf coast.

&&

.MODEL DISCUSSION...
The thing to know about the models today is that they are all
converging toward a common solution with the large low moving
through the area later this week. Yesterday there was a large
difference in track and strength but now they are indicating an
initial low crossing the central Aleutians into the Bering Sea Tuesday
night with a triple point low to the south of this first low. The
triple pint will rapidly swing northeastward bringing much
stronger winds to both the Bering Sea and Gulf of Alaska regions
for Wednesday night into Thursday. Confidence is greatly increased
from yesterday that this solution will work out.

&&

.AVIATION...
PANC...VFR conditions will persist. Light winds should continue
through early Tuesday morning. Wind should turn more southeast
during the morning Tuesday and could gust to the 10 to 15 kt
range.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Monday
night through Thursday)...

The area of active weather continues to be located in the Gulf of
Alaska. Currently a weak frontal boundary is beginning to push on
shore, which will bring rain showers and gusty winds with it to
the Anchorage area. Winds will mainly be confined to the Turnagain
Arm. Warm temperatures will keep the snow level above 2,000 feet,
so any snow will be confined to the mountains with very little
accumulation. Also of note with temperatures, above average
temperatures continue with the observation at Ted Stevens Airport
recording a daily high temperature record of 54F.

The next low will be a significant weather producer as it enters
the southwest gulf on Wednesday. The actual low center will move
northeast up the Alaska Peninsula. However, it will produce gale
force winds for places like Shelikof Strait, Kodiak Island and
Kamishak Bay. These winds will progress northward and increase in
to storm force winds Thursday, with gale to storm force winds
encompassing most of gulf and coastal areas in southcentral AK.
Forecast confidence with this system was a bit shaky yesterday,
but model data has improved since then so we are now confident in
the forecast. We will watch it closely the next few days.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

Rain will continue this afternoon along the AKPEN and Kuskokwim
Delta under a deformation zone. Scattered showers will linger this
evening into Tuesday as it weakens. As such, clearing is likely
along the coast Tuesday morning which will in turn bring the
chance of patchy fog. Areas of thicker, more widespread fog are
possible over interior regions on Wednesday morning with minimal
low level flow and clear skies overnight. A front will approach
the Bristol Bay coast through the day Wednesday and winds will
gradually increase. Gusts along the coast and in channeled areas
could exceed 50 mph by evening. These winds will diminish from
south to north. As a strong upper level jet develops south of the
AKPEN, confidence is growing for a more intense secondary low to
approach the same area on Thursday which has the potential to
bring even higher gusts.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

A weak low will continue to track south of the Aleutians, however
it will be far enough south that sub gales and low seas are
expected to persist through Tuesday morning. Another north Pacific
low will approach the Aleutians Tuesday evening. Latest model
runs have slightly weakened this low as it is transferring its
energy in the process of phasing with another low developing to
its east. That said, widespread gales are still likely Tuesday
night into Wednesday morning east of Atka. Winds will diminish
Wednesday afternoon under the low, then increase again to upper
gales late- evening into Thursday morning as the second low
approaches Bristol Bay. Gales are likewise expected across the
western Aleutians as cold air wraps around the original low.

&&

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

...Gulf of Alaska...

The forecast period starts out on a very active note, with
significant changes made to the forecast for Thursday into Friday.
The numerical guidance has come into much better agreement over
the last 24 hours, facilitating the need for these changes. In
short, sustained winds will rapidly increase to storm force for
most of the coastal waters Thursday afternoon, with a few
hurricane force gusts a distinct possibility for the Barren Islands
region, and just short of hurricane force elsewhere. Given good
fetch length, seas will build into the 15 to 25 feet range, as a
strong front crosses the region from southwest to northeast during
the day. Conditions will rapidly improve for Friday and Saturday.

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

An area of low pressure north of Adak Thursday morning will wobble
eastward while becoming absorbed into a new low racing into the
eastern Bering/western Bristol Bay region later in the day.
Sustained gales will be common for all locations during the day,
with seas averaging in the 15 to 20 feet range. The exception to
this will be from The Shumagin Islands eastward, where some
sustained storm force winds are likely, with some hurricane force
gusts not out of the question. Here, seas will top out in the 25
to 30 feet range. Conditions will gradually improve for Friday
into Saturday.

&&

.LONG TERM FORECAST (Days 3 through 7)...

The weather will become very active on Thursday, as a strong
frontal system crosses the region. This front will be attached to
an area of low pressure moving into western Bristol Bay. Very
strong dry advection wrapping into the low. This combined with a
strong 1.5 mb PV anomaly and favored left exit region jet
dynamics all point to a strong downward mixing potential
environment. Thus, some strong winds will develop near the Alaska
Range across southwest Alaska. Here, look for sustain winds of 30
to 40 with gusts to 55 mph to be possible.

For southcentral, the main wind impacts will be felt through some
passes along the Kenai Peninsula into the Turnagain Arm areas,
where sustained winds of 45 to 55 mph, with gusts to 75 mph may
develop. If the numerical guidance continues to portray this, a
High Wind Watch may be issued for the Turnagain through Portage
area. Some of these winds look to affect the southeastern half of
the city as well, with the highest winds of 30 to 45 mph, with
gusts to 60 mph seem reasonable.

This front will also bring some fairly widespread rainfall, with
the typical rain shadow locations likely just seeing some
sprinkles making it across the Chugach Mountains given the strong
southeasterly flow aloft. This down-sloping effect may give a
boost to the temperatures though, with warm conditions expected to
continue.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 155 165 170 171 172 173 174 175 176 179 413 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RA/EZ
SOUTHCENTRAL ALASKA...BB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP/KVP
MARINE/LONG TERM...PD