Small Craft Advisory 350, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
518 AM AKDT Sun Apr 29 2018

.ANALYSIS AND UPPER LEVELS...
The surface low associated with the strong frontal system that
pushed across the Bering last night has now deepened to 971 mb,
become vertically stacked and is now tracking into the northern
Bering with a trailing cold upper trough rotating into the
western Bering and western Aleutians. The front which has been
bringing strong winds to the Alaska Peninsula overnight and
through the early hours is now pushing onshore over Southwest
Alaska. Over Southcentral Alaska, east to southeasterly flow and
gap winds strengthen out ahead of the frontal system in Southwest
Alaska while a secondary front stalls along the northern Gulf
coast.

&&

.MODEL DISCUSSION...
Although models continue to struggle with timing and track of the
gradually filling surface low as it tracks northeast through or
in the general vicinity of Norton Sound, the net result sensible
weather-wise for Southwest and Southcentral Alaska is pretty
similar for all the solutions. Following this system, synoptic
model agreement is moderately good through midweek as westerly
zonal flow persists across the area.

&&

.AVIATION...
PANC...VFR conditions will persist with breezy southeasterly winds
continuing through midday with winds increasing a bit more in the
afternoon and evening. Additionally, showers will increase in the
afternoon though will be mostly downsloped away. During the early
evening hours however showers will have a better chance to impact
PANC with the potential for conditions to very briefly drop to
MVFR as the main frontal band pushes through.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The windy and wet pattern continues. An occluded front over
western Alaska this morning moves through the Cook Inlet to MAT-SU
corridor this evening and through the Copper River Basin Monday
morning. Most areas will be generally windy with approach and
passage of this frontal system. Winds through favored gaps
(Turnagain Arm, Knik Arm, Along the Copper River, etc.) will
experience the strongest conditions with winds peaking during the
late afternoon to early evening hours. Gap winds will diminish
overnight, but will see a little resurgence on Monday afternoon
and evening as a secondary surface low/trough heads toward the
western mainland and in response increases pressure gradients
across Southcentral.

The precipitation pattern will be a little different with the
front today. Broad southwesterly flow in the mid to upper levels
will favor higher precipitation values with upslope conditions in
the northern Susitna Valley and along the Talkeetna Mountains.
Most lower elevations will see generally rain, though the northern
Susitna Valley and higher elevations will likely see a trend
toward snow. Chulitna north could see a couple of inches of snow
with several inches over the Talkeetna Mountains. Otherwise, most
areas in the shadow of the Chugach will not get much rain until
right around frontal passage. Coastal areas will generally once
again be the big winners. Precipitation across most areas will
tapper off tonight after frontal passage. The threat of showers
continues into Monday. A wave moving north across the Gulf brings
increased chances of rain to the North Gulf Coast and Eastern
Kenai Peninsula Monday night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A fast-moving front tracking northeast across SW Alaska this
morning will continue to advect mild air and moisture into the
region through midday. Widespread rain with a few isolated
pockets of mixed precipitation in interior valleys will diminish
during the afternoon hours as the front continues to push to the
east. Gusty southwesterly winds will develop behind the front as
colder air advects into SW Alaska behind a 971mb low tracking
northeast through the Bering. As the colder air moves in aloft
(850mb temperatures near -8C by 6z Mon) scattered snow and rain
showers will again develop Sunday night. These showers will become
more numerous Monday as a secondary surface trough slides through
the region. Any lingering rain and snow showers will diminish
overnight Monday as weak ridging builds in the wake of the trough.

A long-duration west to southwest flow with gusts approaching
45mph across the Bering Sunday and Monday will act to build seas
along the west coast. Although coastal flooding is not expected,
an SPS has been issued to address the hazard of high surf and
water levels from Kuskokwim to Hooper Bay, especially during high
tide Monday morning.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A 971mb low with westerly storm-force winds on its southern flank
today will continue to track northeast through the Bering today.
Strong upper-level support combined with colder air wrapping in on
the backside of the low will produce gusty westerly winds across
much of the Bering through Sunday evening. A second piece of
energy wrapping around the parent low will develop a weak surface
trough across the central Bering for Monday. This will enhance
the threat for snow showers around the Pribilofs Monday afternoon
and evening. By Monday afternoon, another, weaker low will begin
to develop near the western Aleutians. This will track toward the
central Bering by Tuesday.

&&

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

The largely east to west weather pattern currently ongoing across
Alaska will continue for the start of the long-term forecast
through the first week of May. A weak low over the central Bering
Tuesday morning will quickly track eastward and move into Bristol
Bay by Wednesday morning. While the surface energy dissipates,
the upper level energy will continue into Southcentral, resulting
in Wednesday afternoon showers for much of the area. Meanwhile,
another stronger low strengthens across the central Bering
Wednesday evening. This low will flip the pattern to a more
amplified one, which in turn will result in the weather remaining
more consistent day-to-day going into the weekend.

While there are large model differences in the details, such as
where precipitation will be or how strong the low or trough will
be for example, the one consistency between the models is that the
low or deep trough anchors itself along the Bering coast of
Southwest Alaska. That would keep Southwest Alaska continuously
chilly and unstable from Thursday onward. For Southcentral, the
weather will be somewhat warmer, but cloudy and wet as continuous
southerly flow off the Gulf keeps a steady stream of moisture
moving into the area. The wet pattern would be quite unusual for
this time of year given that this is typically the dry season.
Strong ridging builds over the western Bering by Saturday which
will further amplify and slow down the pattern.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storms...185.
		 Gales...177 178 179 180 181.

&&

SYNOPSIS AND MODEL DISCUSSION...JR
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
LONG TERM...JW