Small Craft Advisory 177, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
440 AM AKST Sat Mar 2 2019

.ANALYSIS AND UPPER LEVELS...
The latest Nighttime Microphysics satellite image has an area of
fog and low stratus over Prince William Sound and a second area of
fog over portions of western Alaska. The remnants of a frontal
boundary have moved into the AKPEN and Kodiak and are pushing up
Cook Inlet. There is a new vigorous low near Attu Island and the
latest ASCAT/Advanced Scatterometer has detected gale force winds
with this system. Looking aloft, one finger of the jet is over the
Bering Straight while a strong jet core is southwest of Shemya.
The radars at Bethel and King Salmon do not look very active but
there may be some below beam precipitation occurring with that
front slowly pushing through the state. The radar at Middleton
Island has detected showers this morning.

&&

.MODEL DISCUSSION...
The global models continue to be in good agreement through 00z
Tuesday with the major synoptic features. There are some minor
model differences with the upper trough trekking across Southwest
Alaska and Southcentral Alaska but the impacts would be
negligible. The main event is the new storm approaching the
Western Aleutians and the models are in sync with that one and the
next one that will be east of Japan and very quickly near Attu on
Tuesday.

&&

.AVIATION...
PANC...At 10:53Z or 1:53 AM AST a low deck was observed at PANC
and at 3 AM AST fog was observed at the National Weather Service
Office. Again tonight low stratus was observed on the Mt Baldy
webcam. With the melting that took place yesterday, there is
enough available low level moisture for fog development. This
situation is actively being monitored. If fog does form over the
airport, it is expected to dissipate late morning. The good news
is the remnants of a frontal boundary are currently moving up Cook
Inlet and this will mix the atmosphere up, resulting in a respite
in fog for PANC for tomorrow morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Upper level high pressure will remain over the area today. This
high pressure is fairly weak and plenty of low level moisture is
over the northern Gulf and the Prince William Sound area in the
form of low to mid level clouds and some snow showers, which will
continue through Sunday morning. An eastward moving upper level
trough will "top" the ridge tonight into Sunday morning. This
will bring increased cloud cover across the area. Most inland
areas will not see precipitation, except possibly the Susitna
Valley and the southern Kenai Peninsula. Precipitation will clear
out of the area by late Sunday afternoon as the trough moves east
and dissipates. High pressure will then build in from the west
Sunday night with clearing skies.

&&

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

A dying front over the Lower Kuskokwim Valley and Bristol Bay will
continue to keep that area under mainly cloudy skies for much of
the day as it inches eastward over the Alaska Range today and
dissipates. Behind the front, areas of fog are present across the
Kuskokwim Delta, which should break up somewhat with diurnal
heating late this morning. Any remnant precipitation is very
light. Temperatures for most areas should rise well into the 30s
again today along the coast with mid-30s inland.

Sunday will feature a mix of clouds and sun between systems. The
next front will approach from the west late in the day which will
help increase cloud cover once again, along with slowly ratcheting
up the southerly winds along the coast as well. Rain and snow will
begin moving into the Kuskokwim Delta around sunset Sunday
evening. Rain and snow are expected with the front moving inland
Sunday night, as temperatures hover right around freezing. Despite
the gusty winds associated with the front, those warmer
temperatures should keep there from being any blowing snow
concerns where precipitation remains all snow. Like its
predecessor, this front too will have trouble making too much
inland progress, though southeasterly winds will allow for an
upslope component to help with precipitation rates from Koliganek
westward through the day Monday. A low tracking well off the coast
Monday night will turn the winds out of the west behind it, which
will finally help the stalled out front resume its eastward motion
by Tuesday. The low will help continue to pump in warm air as
south to southeasterly winds continue through Monday. This will
help turn precipitation in many areas, even well inland, over to
rain during peak heating Monday afternoon. Those areas that stay
all snow should see only a couple inches of very wet snow from
this system.

&&

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

The leading front associated with a strong low is currently
pushing eastward across the Central Aleutians this morning. The
front is causing widespread gales with some embedded storm force
winds as it moves eastward. The center of the low is expected to
track just west of Attu this evening as it continues northward to
the coast of the Kamchatka Peninsula by Sunday evening. Along this
track, the north to south oriented leading front will move into
the Pribilofs late tonight, with a weaker portion of the front
reaching Unalaska Island Sunday morning. Winds with the front will
rapidly diminish over the eastern Bering Sunday night. Meanwhile
the wind field associated with the low itself will move into the
Western Aleutians late this afternoon, causing another round of
storm force winds through Shemya through much of the night. As the
low lifts northward, the winds will diminish there through the day
Sunday. A secondary low will develop along the weakening front
Sunday night over the North Pacific and intensify as it tracks
north from Unalaska by the Pribilofs Monday afternoon and into the
northern Bering Monday night. The low will help the front
continue eastward into Southwest Alaska. A showery weather regime
will set up over the western Bering once the Kamchatka low
departs and weakens on Monday. Another strong low looks to impact
the western Bering and Aleutians late Tuesday. More on that below.

&&

.MARINE (Days 3 through 5)...

Sub gales are generally expected over the Bering Monday, although
isolated gales are possible over the western and eastern Aleutians
near a weak low. A strong, broad low pressure system will move
into the western Bering Tuesday afternoon. Confidence is moderate
to high that upper end gales, potentially reaching storm force,
and high seas will persist through Thursday over the western
Aleutians, peaking overnight Wednesday into Thursday. The central
and eastern Aleutians are less likely to see storm force winds
further from the low center, however gales and higher seas ahead
of the associated front will track west to east on Wednesday
before gradually subsiding on Thursday as the front weakens.

Sub gales are expected for the Gulf through Tuesday north of high
pressure. There is a slight chance of gales near the Barren
Islands on Wednesday (mainly in the morning) west of a weak low.
Confidence is low at this time as models disagree on its strength
and position, which is typical for smaller scale features this
far in advance.

&&

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

A front associated with a weakening low over Siberia will move
into the eastern Aleutians and western mainland Alaska on Monday.
The precipitation will persist through Tuesday as another weaker
low will aid in transporting more Pacific moisture into the
region. The greatest uncertainty remains the precipitation type.
Continued southerly flow is expected throughout the event, however
surface temperatures will be just above freezing for many areas
away from the coast. Thus, it is difficult to determine which
areas will see a rain/snow mix and which will see all snow. If
models do verify colder than current guidance, then significant
snow accumulation could occur. However, given the aforementioned
strong southerly flow, confidence regarding accumulating snowfall
across coastal areas of the southwest mainland is low at this
point. As the front departs the western mainland, a strong low
will move into the western Bering and confidence is high that
moderate to locally heavy rain will track west to east across the
Aleutians through Thursday. The active pattern is expected to
continue into next weekend.

Generally fair skies expected across Southcentral Alaska Monday
under a ridge. As expected, the ECMWF solution came into more of
a consensus with the GFS regarding a low tracking west of Bristol
Bay on Tuesday. This is expected to bring widespread precipitation
to the region through Wednesday morning. As discussed above,
precipitation type is difficult to determine at this time, though
significant snow is likely over higher elevations. A ridge will
build in behind the front Wednesday afternoon through Thursday,
with the next system moving into Southcentral by Friday. Though
model timing agreement degrades, the overall active pattern with
likely precipitation should continue into next weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storms 413 411 178 177 176 175. Gales 414 412
170 172 173 174 179 181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
MARINE/LONG TERM...AP/KVP