Small Craft Advisory 188, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
533 AM AKST Tue Feb 25 2020

.ANALYSIS AND UPPER LEVELS...

An upper level ridge axis lies along 61N from Russia to the Yukon
border. A stacked 973 mb storm force low in the North Pacific
south of Kodiak Island continues its march northeastward, the
first bands of precipitation are reaching Kodiak. Another 977 mb
stacked low sits in the North Pacific southwest of Shemya.

&&

.MODEL DISCUSSION...

Models have generally agreed on the path of the low as it tracks
into the Gulf of Alaska this morning. Some disagreement arises as
the low approaches Middleton Island Thursday morning, with the GFS
keeping a more westward track. The North Pacific low southwest of
Shemya is also fairly consistent on the recent runs with some
deviation in its dissipation on Wednesday night into Thursday
morning.

&&

.AVIATION...
PANC...VFR conditions and gusty northerly winds will persist
through the day today.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
(Today through Wednesday evening)

A low south of Kodiak Island continues to produce storm force
winds ahead of the front for the Barren Islands, Shelikof
Straight, and the southern coastal waters of Kodiak Island.
Speaking of Kodiak, the trend over the last several hours at the
airport has been for winds to gust to near 60 mph with snow and
blowing snow, reducing visibilities to less than one mile. This
trend should continue through about noon, before winds
decrease as the low pressure center approaches. Extending to the
northeast from this low, towards Prince William sound and the
Valdez Narrows/northern Gulf Coast, is an approaching front.

The Middleton Island Doppler radar shows the precipitation
associated with this front making inroads into the Copper Basin
and coastal locations. Meanwhile, the Thompson Pass observations
continue to show winds peaking in the 60 to 65 mph range, which is
likely causing some blowing snow and reduced visibility issues.
Here too, winds should slowly decrease through the afternoon,
before diminishing more quickly this evening as the front
approaches.

For the remainder of Southcentral, winds have occasionally been
gusting above 20 mph near Palmer, as the tight pressure gradient
induced by the approaching front and cold air continuing to funnel
through the passes from the Copper Basin interact to allow for a
Venturi Effect (the increase in wind speeds due to the air
being forced through a more narrow outlet) to keep
this persisting from time to time for the next few hours.

Snowfall from the approaching system should encompass all of
Prince William Sound, the eastern 2/3rds of the Kenai Peninsula,
and at least eastern portions of the Anchorage Bowl/Matanuska
Valley. The snowfall and winds will continue to diminish on
Wednesday, as the low moves into the central Gulf and weakens,
with surface convergence also diminishing as frontolysis (the
dissolving of a front) ensues, with orographic lift/onshore flow
continuing to help give localized boosts to the precipitation
along the coast and the southern and eastern slopes of the
mountains.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 2)...

At the onset of the forecast period, the pattern features a
1040 mb surface high over the interior with a mature low of
971 mb south of the Alaska Peninsula. The enhanced pressure gradient
will result in gusty winds over Bristol Bay and portions of
Southwest Alaska. The models do wrap some moisture into the AKPEN
with this system but most of the region will remain dry this
forecast period. Temperatures will continue to run slightly below
normal.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 2)...

A storm force low moves south of the eastern Aleutians and Kodiak
this morning. There is a second mature low south of Attu Island
with a frontal boundary bisecting the Bering and the Aleutian
chain. This front will bring a second wave of unsettled weather to
the region. However, as time elapses the models show the low
decaying and slowly pushing eastward this forecast period. Broad
cyclonic flow will continue to impact the chain with intermittent
precipitation.

&&

.MARINE (Days 3 through 5 Thu through Sat)...
Winds look to remain below gale force from Thursday through Friday
morning. Later Friday a strong system will move into the western
and central Aleutians, and into the Bering Friday night and
Saturday. This system will bring gale to possibly storm force
winds across the western and central Aleutians and most of the
Bering Sea. On Friday night there is also a chance of some
westerly gales through the Barren Islands area.

&&

.LONG TERM FORECAST (Days 4 through 7 Fri through Mon)...
On Friday morning the pattern will consist of an eastward moving
trough over western Alaska, an east to west oriented ridge across
the central Bering, and a deep trough southwest of the western
Aleutians. On Friday the western Alaska trough slide east across
the area and weaken. A deep upper low in the western trough will
move northeast into the western Aleutians Friday night then into
the Bering on Saturday. This will turn the flow aloft to southwest
over the eastern Bering through southern Alaska, with a fairly
consolidated jet pushing northward. This will result in a fairly
active pattern Sunday and Monday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 131 171.
MARINE...Storm Warning 130 131 132 136 138 150
         Gale Warning 119 120 127 128 137 139 155 160 165 351 352
                      411 412
         Heavy Freezing Spray 139 179 180 185
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...LTB
SOUTHCENTRAL ALASKA...PD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS
MARINE/LONG TERM...BL

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1136 AM AKST TUE FEB 25 2020

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

1130 AM     SNOW             1 ESE KODIAK            57.79N 152.39W
02/25/2020  E5.0 INCH        KODIAK ISLAND      AK   OTHER FEDERAL

            SPOTTER REPORTED 4-6 INCHES OF SNOW AS WELL
            AS SNOW BLOWING AND DRIFTING.

&&

MV

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1137 AM AKST TUE FEB 25 2020

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

1130 AM     SNOW             2 SE KODIAK STATION     57.74N 152.50W
02/25/2020  E3.5 INCH        KODIAK ISLAND      AK   OTHER FEDERAL

            SPOTTER REPORTED 3-4 INCHES OF SNOW ALONG
            WITH BLOWING AND DRIFTING SNOW.

&&

MV