Small Craft Advisory 150, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
435 AM AKST Thu Feb 15 2018

.ANALYSIS AND UPPER LEVELS...
An upper level trough over eastern mainland Alaska continues to
push off to the east towards the ALCAN border this morning. Snow
has tapered off over Southcentral while light snow continues over
the Copper River Basin. An upper level ridge is building in
behind the departing trough leading to clearing skies with
widespread areas of fog developing over southwest Alaska and more
recently over the Cook Inlet and the Kenai Peninsula. Further
west, an upper level trough is digging NE across the Western
Aleutians with an associated surface low and frontal system
sweeping across the Central Bering towards the southwest mainland,
bringing gale force winds and rain to the area.

&&

.MODEL DISCUSSION...
Models have come into decent agreement with the evolution and
progression of the longwave pattern over the next couple of days,
with high pressure building in over the central and eastern
portions of the mainland and a more progressive and stormy
pattern out west. Recent model runs have steered away from a more
northward storm track as systems move from the Bering into the
Gulf, which would deflect storms to the south keeping
southcentral in a high and dry pattern heading into next week.

&&

.AVIATION...
PANC...Snow has tapered off overnight as the longwave trough
pushes east, though a rapidly building ridge behind it will trap
low level moisture leading to IFR/LIFR Cigs and the likely
development of fog by 15Z. With fog already developing over Kenai,
conditions are obviously ripe for widespread development over the
Cook Inlet area and into the Anchorage bowl. The densest fog may
take some time to develop this morning as left over low stratus
will slow cooling at the surface, but the building ridge combined
with recent precipitation will eventually take over and should
lead to widespread fog development this morning before lifting in
the afternoon.

&&

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

An upper trough and associated surface front will clear the Copper
River Basin this afternoon. Snow and snow showers will likely
continue with these features as it pushes east. Low stratus and
fog will likely hang around upper Cook Inlet, Anchorage Bowl, and
MAT-SU Valleys this morning with improvement this afternoon. Areas
of stratus and fog could redevelop again tonight across the
Anchorage Bowl and perhaps as far as Palmer in the Mat Valley as
light winds and upper ridging strengthen surface inversions.
Brisk/strong outflow winds will develop over the eastern Kenai
Peninsula/Western Prince William Sound and the North Gulf Coast
this morning and should peak this afternoon before weakening
overnight.

A surface front spreads rain to the western Gulf tonight. The
north progression of the front should stall Friday as a strong
triple point low develops and pulls the front southeast. So
precipitation, mostly snow, will likely only make it as far north
as the Kenai Peninsula before the surface low carries it
southeast. Pressure gradients will once again build along the
Gulf coast and give rise to another round of outflow winds Friday
night.

 &&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Some areas of lingering cloudy conditions and fog will persist
through this morning, as the residual moisture from the previous
system remains over some areas which cleared out overnight prior
to fog developing. Our focus quickly shifts to an approaching
front pushing into the southwest Mainland starting this afternoon.
This system will weaken as it progresses eastward through Friday,
bringing widespread precipitation to much of the area and mainly
in the form of snow. However, frontal speed will temporally limit
any snowfall accumulation potential, with just light amounts
expected. By Friday evening a weak area of high pressure will
build in over the mainland, and bring another round of clearing
skies and drier conditions through Saturday morning.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A 979mb low will continue to track northward through the central
Bering through tonight bringing widespread gusty winds and
precipitation to much of the Bering and Aleutians through this
evening. The associated front currently stretching from the
Pribilof Islands through the eastern Aleutians will continue to
spread gusty winds and precipitation over the eastern Bering/
Aleutians and Alaska Peninsula into Friday morning. Right on its
heels is another gale force system working its way into the
western Aleutians by this afternoon, and spreading strong gusty
winds and precipitation eastward into the central Bering/Aleutians
overnight tonight into Friday morning.

&&

.LONG TERM FORECAST (Days 3 through 7)...
As a decaying front across the Anchorage area slides East on
Friday afternoon, only a slight decrease to temperatures and
increase of clouds are to be expected. Temperatures aloft will
cool through that time but begin to rebound into the weekend and
beyond. Skies are expected to clear out by the early weekend. Now
that we are back into the season of the sun helping to aid in
warmth, daytime temperatures will quickly rise. Diurnal swings of
20 degrees, or more, are not out of the question. Interior and
river valley areas of the Copper River Basin should see night
temperatures drop well below zero as any warmth radiates out
overnight. Clouds will increase Sunday afternoon with an
approaching front from the West. However, guidance has a harder
time figuring out how far the front will move to the east. If it
has enough oomph to overtake the ridging over the area, we may see
snow Monday afternoon into the evening hours. The GFS is showing
the strongest of these signals. The EC is indicating a much weaker
front with light snow, and the Canadian is showing nothing.
Regardless, the nature of ridging and troughing will continue
progressively through this weekend and into next.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Heavy Freezing Spray Warning 181.
         Storm Warning 175-177 413.
 Gale Warning 165 170 173 174 178-181 185 352 411 412 414.&&

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

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1016 AM AKST THU FEB 15 2018

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

1012 AM     SNOW             5 ESE WASILLA           61.56N 149.32W
02/15/2018  M2.5 INCH                           AK   CO-OP OBSERVER

1012 AM     SNOW             SUTTON                  61.72N 148.88W
02/15/2018  M2.0 INCH                           AK   TRAINED SPOTTER

            SNOW BEGAN AT 345 PM. DURATION WAS 6+ HRS.

&&

LF

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
152 PM AKST THU FEB 15 2018

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

0151 PM     SNOW             POTTER VALLEY           61.05N 149.79W
02/15/2018  M2.3 INCH        ANCHORAGE          AK   PUBLIC

&&

KH