Gale Warning 286, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
447 AM AKDT Tue Apr 9 2019

.ANALYSIS AND UPPER LEVELS...

Generally calm conditions are the rule across Southern Alaska this
morning. Shower activity that produced thunderstorms yesterday
evening continues across the Copper River Basin and Susitna
Valley. Rain is also off-and-on along the North Gulf Coast. A pair
of weak lows are also present. The stronger of the two is tracking
well south of Kodiak Island. The other is a swirl of clouds
northwest of Dutch Harbor. Otherwise generally mostly cloudy to
cloud skies persist for much of the area as southerly flow
transports Gulf moisture into Southern Alaska. The only features
of note in the upper levels consist of the upper level support for
the weak low south of Kodiak Island, and broad troughing over the
western Bering. The subtropical jet is primarily tracking in
zonal flow to the south of the Aleutians.

&&

.MODEL DISCUSSION...

The models are coming into better agreement with the track and
strength of a North Pacific low that will reach peak intensity as
it approaches the Alaska Peninsula and eastern Aleutians on
Wednesday night. Much beyond that however, increasingly
significant differences appear and quickly become worse with time.
Among those differences include the strength of the low as it
tracks into the eastern Bering. The GFS is the strongest with a
central pressure near 960 mb. The 06Z NAM is much closer to the
model consensus than its 00Z counterpart, yet it is still among
the weakest solutions with a peak intensity of 968 mb. The
significance of this difference mainly includes how strong the
winds near Kodiak Island get when the leading front passes by
Wednesday evening. It will also impact how strong the winds get on
Thursday through Turnagain Arm and the gaps. While the front
will be quite strong regardless of the model solution, the
expected track of the parent low in a cyclonic loop should
mitigate the impacts and how strong the peak winds associated with
the front get on Thursday. While forecast confidence is improving,
there still remains enough disagreement that it's about average.

&&

.AVIATION...
PANC... Rain showers moving over the area will continue into the
early morning hours. Temporary gusty conditions are possible as
well. The showers will diminish through the early afternoon, then
some redevelopment is possible with afternoon heating. All
activity will end towards sunset.

&&

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

A weak frontal boundary draped along the southern mainland slowly
diminishes through the morning. Light rain showers, with snow
showers along higher elevations taper off by early afternoon.
Another front along the southern Gulf moves east by late
afternoon. A ridge builds across Southcentral this evening keeping
the region dry through Wednesday. The exception to this will be
across Kodiak Island and the southern Kenai as a North Pacific
front lifts north to the Bering. East to southeast winds begin to
increase across the western Gulf and northerly flow for Cook Inlet
Wednesday evening with pre-frontal showers before midnight. The
frontal boundary makes quick progression after midnight with gusty
gale force winds developing across much of the Gulf along with
moderate rain.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...

A weakening deformation zone aligned over Southwest continues to
bring precipitation to the interior Bristol Bay region up to the
lower Kuskokwim Valley. A ridge building to the east will bring
the chance for fog this morning in Bristol Bay...this will depend
on whether there are enough breaks in high clouds to cool surface
temperatures to the dewpoint. Showers will diminish this afternoon
and steady south flow will cause high temperatures in Bristol Bay
and the Kuskokwim Delta to trend several degrees warmer than
yesterday. Farther inland, lingering cloud cover will limit
heating somewhat. A low approaching the central Aleutians from
the north Pacific will spin a front into the AKPEN Wednesday. This
front will be relatively inconsequential in terms of
precipitation, however expect strong southeast winds, associated
with the front, with gap winds potentially gusting to 40 kt. In
addition, warm air advection and downsloping will bring
temperatures to the upper 40s in low lying areas of Southwest.
Another front with a much deeper moisture fetch will approach
Southwest Thursday. Expect another round of strong winds with
this, with gusts again possibly reaching around 40 kt, but expect
widespread precipitation over Southwest.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2: Today
through Thursday)...

The quiet weather ongoing across the Bering this morning will come
to an end late this afternoon as the first of a pair of lows moves
out of the North Pacific and into the central and eastern
Aleutians tonight. As the first low weakens and tracks west, a
second even stronger low will track between Dutch Harbor and Cold
Bay on Wednesday night. This low will have storm force winds to
its south as it reaches peak intensity Wednesday night. Widespread
gale force winds are expected along the Pacific side of all of the
Alaska Peninsula and eastern Aleutians. Strong southwesterly onshore
winds will also impact Bristol Bay, which may result in some
coastal flooding concerns. Otherwise most areas can expect gusty
soaking rains through Thursday across much of Southwest Alaska.
With the models rapidly diverging on the track of the low by this
point, larger changes to the forecast are very possible for
Thursday and beyond regarding the low track.

&&

.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 Warning: 150-176, 179-185, 412-414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JPW
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MM/JPW
MARINE/LONG TERM...PD