Small Craft Advisory 196, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
424 PM AKST Sun Mar 4 2018

.ANALYSIS AND UPPER LEVELS...
A progressive pattern remains in place over Alaska and the Bering
Sea. There is an upper level ridge over mainland Alaska with an
upper trough over the Bering Sea. A north-south oriented front is
moving into southwest Alaska from the west with some precipitation
in the coastal areas moving inland. Offshore flow over
Southcentral Alaska is keeping outflow winds over the preferred
areas such as Whittier, Seward and Valdez. These winds are
beginning to weaken as the southwest front approaches. A showery
regime is in place within the trough over the Bering.

&&

.MODEL DISCUSSION...
The numerical models are in fairly good agreement through the
short term portion of the forecast (Tuesday afternoon). There are
some minor differences in how the models handle the speed and
precipitation with the front moving through Southcentral on
Monday. Forecast confidence is thus a little above normal.

&&

.AVIATION...
PANC...VFR conditions and light winds are expected. Some snow
showers are possible Monday afternoon and evening, but most likely
will be east of the airport.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2...Mon and
Tue)...
The pattern continues to be remarkably consistent. After Saturday's
snow, fog and low stratus set up through much of the morning
across Southcentral AK. Then, the next in the series of
shortwaves will move through tomorrow morning before we see
another round of fog and low stratus late Mon night into Tue.
First off, the stratus that plagued the area this morning has
mostly burnt off. It is still holding in some of the deeper
valleys such as the Knik and Copper River. It should clear mostly
out of the Knik Valley, but has good potential to hold on in the
Copper River Basin with light winds and increasing stability.

Monday's shortwave is currently over the West Coast. It will
track over the AK Range into Monday morning and move east into
Southcentral. The forcing associated with this system will be very
broad and weak as it passes over Cook Inlet. With westerly flow,
it will struggle to bring much moisture over the AK Range. Thus,
have continued the approach for the best chance of accumulating
snow to be along west facing slopes of the Chugach and Talkeetna
Mountains. Chose to limit much of Anchorage and the Kenai
Peninsula to just scattered snow showers. This shortwave
intensifies as it moves east over the northern Copper River Basin,
so can't rule out an inch or snow of snow in that area.

Monday's system will be followed by another weak offshore flow
event. So expect gusty winds once again Monday evening into
Tuesday through Whittier, Seward, Thompson Pass, and the other
usual suspects. By Tuesday afternoon, the next front is already
tracking across the Alaska Range. While not overly impressive,
this system will certainly have better lift and more moisture than
its predecessor. Thus, expect another widespread light
accumulating snow event across our region.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA...
The progressive pattern continues. There is a surface low over NE
Russia with a frontal boundary extending from it basically from
Nome to the AKPEN. The latest satellite image has a broad
associated cloud shield and the radar at Bethel (PABC) continues
to be active. Snow is definitely making it to the ground for
portions of SW AK. The radar at King Salmon (PAKC) has pinged into
a few showers, but the most active portion of the front is north
of Dillingham...which is what the models had projected. This
frontal boundary will decay tonight and tomorrow as it pushes
inland. Weak ridging will then move in before another front comes
on Monday night. This front will also impact the Kuskokwim Delta
and bring more blowing snow to the area. However, this system is
stronger with higher snow amounts and stronger winds expected.
This will result in reductions in visibility that could reach one
mile or less. There is some concern about potential blizzard
conditions, but it is still too early to make that call given the
vagaries of the models.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS...
The front over the eastern Bering will quickly push off to the
east. In its wake, there is weak progressive ridging. Down range,
a developing low near southern Kamchatka will mature. As this low
treks north-northeastward the frontal boundary will move into the
Bering bringing gales. This system will steer a fetch of warm
moist air from the south and looks to bring a mix of rain and snow
to the islands. The front will move east making it to the central
Bering and Aleutians Monday afternoon and the eastern Bering and
Aleutians by Monday night. Westerly flow with showers will be left
in the wake of this system through Tuesday.

&&

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

Beginning the extended period forecast Tuesday evening, the
region will be under the influence of a continued progressive wave
pattern as another trough moves across the state. This system
will be moving east across the Alaska Range, and this looks to
bring widespread light snow to Southcentral Tuesday evening into
Wednesday morning. That system moves east Wednesday, then
attention shifts to a much stronger and dynamic low moving east
across the Bering Sea. This powerful low will track an occluded
front into Southwest Wednesday, bringing widespread rain and snow
to the region. The forecast becomes trickier Wednesday night and
Thursday as a triple point low forms in the Gulf of Alaska along
the left exit of a powerful North pacific jet stream, and along a
rather sharp warm front/baroclinic zone. The general consensus is
that a powerful low will form in the Gulf, but placement is rather
disparate at this time. Regardless, this low has the potential to
bring widespread snow to Southcentral, including strong winds
along and near the coast, but until the placement of the low is
better known, this forecast will remain more general until details
can be hammered out. The upper jet will move south again behind
this strong low, so winter will maintain it's grip as colder air
settles in again over all of Southern Alaska.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...
GALES... 177 179 185
STORM... 178

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...MO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS
LONG TERM...JA