Small Craft Advisory 153, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
449 AM AKST Fri Feb 16 2018

.ANALYSIS AND UPPER LEVELS...
The upper levels over Alaska are dominated by a longwave trough/ridge
couplet with the ridge axis located over Southcentral extending
north into Northern Alaska and the trough axis located over the
Eastern Bering Sea. A triple point low is located over the
Northern Bering with an associated front sweeping across the
western mainland bringing snow to the Kuskokwim River Valley and
south into the Bristol Bay area. Over Southcentral, low stratus
and patchy fog persists throughout the Cook Inlet area even as a
cirrus shield spreads east into the region. Further west, a strong
gale force low is barreling east across the Western Aleutians and
Bering, bringing strong winds and heavy rain/snow to the area.

&&

.MODEL DISCUSSION...
The models are in lock step with the overall pattern as ridging
sets up over central and eastern portions of the mainland,
diverting the main storm track to the south while an active
pattern persists over southwest and the Bering. There is some
disagreement with an upper level trough moving through on Sunday
with some models keeping the trough intact and further north,
bringing snow to southcentral, while other solutions have the low
splitting off to the south over the Gulf, which would keep most
of the region dry.

&&

.AVIATION...
PANC...Stratus will continue to be the main issue this morning as
low level moisture is trapped under an elevated subsidence
inversion due to ridging aloft. Northerly winds are helping to
keep the boundary layer somewhat mixed, limiting fog development,
but LIFR Cigs will be present through the late morning with little
forcing to clear things up. Cigs should lift some later this
afternoon with increasing solar insolation this time of year, but
ridging builds back in tonight leading to the potential for more
fog and stratus, though offshore northerly flow may dry things out
enough to keep this from happening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
An upper trough just west of Kodiak Island will close off into an
upper low over the Gulf around noon today as it squeezes
underneath the upper high over Southcentral. This low will then
rapidly move east-southeast across the Gulf this afternoon and
evening. Precipitation with this system will fall over Kodiak this
morning, with the precipitation shield possibly getting as far
north as Homer. The upper ridge will then re-assert itself over
southern Alaska. This should provide enough northerly flow to
clear out the stubborn cloud deck over the Cook inlet area.
Another trough will push into the area from the west on Sunday,
with precipitation reaching Kodiak Island in the morning. There
are some model differences in how this system is handled Sunday
afternoon. The GFS and NAM are repeating what today's system is
doing, in splitting the energy and closing off a low over the
Gulf. The other models bring enough of a trough across the
Southcentral mainland to bring some precipitation inland. For now,
the forecast splits the difference with some "chance" and "slight
chance" Pops over the area.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The active weather pattern looks to continue through the weekend,
starting with the ongoing system tracking further inland over the
southwest Mainland this morning. Snow has remained the dominant
precipitation type for much of the mainland, and is expected to
persist through this afternoon. However, there is a chance for
some rain to mix in with the snow south of King Salmon today.
Some gusty winds will develop for a few locations on the Bristol
Bay coast. However, coverage remains limited for any mention of
blowing snow in the forecast zones.

Otherwise, another short-wave ridge will build over the region for
tonight through Saturday time frame. The next system that will
affect the area will track into the southwest Mainland late
Saturday night into Sunday, with winds and precipitation potential
rising once again.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A series of low pressure systems will continue to affect the
region through the weekend. As the initial Bering Sea low exits
to the north this morning, the next system and its associated
front will quickly stall over the western portion of the
Aleutians and Bering. This system will bring gale to storm force
winds mainly over the central Aleutians and Bering today before
diminishing as the front weakens. The second system of interest
tracks into the eastern Aleutians from the north Pacific overnight
tonight into tomorrow morning and continues to progress north-
northeastward into Sunday before pushing inland.

Quickly following on its heals, the next system developing south
of Shemya will intensify as a 970mb low on Sunday, with another
front arcing east and southward through the west central
Aleutians. Each front will bring an increase in precipitation
coverage and intensity, as well as increasing winds, most of which
will be gale to occasional storm force.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The remnants of the front will push through south central Alaska
Sunday night resulting in increased chances for snow. A low will
be over the north Gulf Coast, but has been the theme of this
current pattern, this low will be deflected to the southeast by
the high pressure over the eastern mainland and Yukon Territory.
Out over the Bering Sea as one low is exiting to the northwest,
another is sliding north across the western Aleutians Sunday
night. The associated front pushes into the northern Bering Sea
arcing south across the eastern Aleutians. The warm front will
push northeast across southwest Alaska by Monday with the
potential for rain or a rain snow mix over southwest Alaska for
the early part of next week. The warm air is progged to push well
inland over the upper level ridge to the Brooks Range through
Tuesday and Wednesday, thus a continuation of this wetter and
warmer trend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm Warning 177.
Gale Warning 132 150 155 165 170-176 178-181 185 352 411-414.

&&

SYNOPSIS AND MODEL DISCUSSION...KVP
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...SA

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
110 PM AKST FRI FEB 16 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1249 PM     SNOW             DILLINGHAM              59.06N 158.53W
02/16/2018  E4.0 INCH                           AK   LAW ENFORCEMENT

            AROUND 4 INCHES OF SNOW FELL OVERNIGHT THURSDAY.

1249 PM     SNOW             ILIAMNA                 59.78N 154.87W
02/16/2018  E5.0 INCH                           AK   OTHER FEDERAL

            FLIGHT SERVICE ESTIMATED 4-5 INCHES OF SNOW FELL LATE
            THURSDAY NIGHT INTO FRIDAY MORNING.

1000 AM     SNOW             N KING SALMON           58.74N 156.54W
02/16/2018  M4.0 INCH                           AK   LAW ENFORCEMENT

            4 INCHES OF SNOW FELL FROM 11 PM THURSDAY NIGHT TO 930
            FRIDAY MORNING.

&&

DPERCY