Small Craft Advisory 947, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
502 PM AKST Mon Dec 9 2019

.ANALYSIS AND UPPER LEVELS...
The surface low dropped to a central pressure close to 950 mb
today and it moved out of Bristol Bay toward Nunivak Island. The
front associated with this low is slowly moving from south-to-
north through Southcentral Alaska today. This front is the source
of the strong winds and heavy rain over the region.

&&

.MODEL DISCUSSION...
Models are still doing well with the synoptic pattern into late in
the week. The exception is the GEM model which is significantly
different by Thursday night and is not being incorporated into the
forecasts.

&&

.AVIATION...
PANC...Gusty southeast winds should have moved into the airport by
late this afternoon. These winds are expected to persist through
the evening and then significantly diminish around midnight. There
is the potential for MVFR ceilings after midnight.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2: Monday
night through Wednesday)...

Low pressure continues impact Southcentral Alaska, bringing high
winds and heavy rain to areas of our forecast area. Specifically,
winds have been gusting down Turnagain Arm to Hurricane Force at
times. A high wind warning remains in effect until 600PM AKST
tonight as a result. Other areas around the Anchorage Bowl
experiencing windy conditions are the upper hillside, Eagle River
and Palmer/Wasilla area. Winds will die down tonight as the low
pushes north.

As far as precipitation goes, coastal regions have been receiving
quite a bit of precipitation in the form of rain with the very
warm temperatures we have been seeing today. Some areas - mainly
the Kenai Peninsula - have received us much as two inches of rain,
including a spotter report near Homer of 1.9 inches earlier today.
Rain will continue through the rest of the day. This amount of
rain (also melting the snow) has prompted the River Forecast
Center to issue a flood advisory for the Anchor River until 1215PM
tomorrow. We are expecting rain to taper off tonight as the low
pushes north, though streams will remain high into tomorrow.

After we get past tonight, we'll catch a brief lull in the weather
before the next system comes in Wednesday. The next round of
weather will arrive in similar fashion with another low sending
weather towards the coast out of the Gulf of Alaska. This next low
will be located farther east and will not be as strong as what we
are seeing today. What this means for our forecast area is more wind
and rain midweek.

&&

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

A 954 mb low just south of Nunivak Island will move offshore into
the Bering through Tuesday morning. Meanwhile, winds will
diminish by midday Tuesday for coastal locations. An area of
blowing snow between Kipnuk and Hooper Bay, as well as on Nunivak
Island, will develop overnight Monday and should taper off by
Tuesday morning. Tuesday will otherwise be a quiet period for
Southwest Alaska before another north Pacific low enters the area
on Wednesday. Forecast guidance suggests precipitation crossing
the Alaska Peninsula Wednesday morning, however the continued
northern extent of precipitation is somewhat uncertain based on
the storm's track. Highest amounts of rain are offshore at this
time, but any shift in the storm's path could affect this. Extensive
warm air from the Pacific suggests a mostly rain event at this
time.

&&

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

The low pushing offshore in western Alaska will bring strong winds
to the north Bering through Tuesday night. Strong cold air
advection in the western Bering will be responsible for snow
showers across much of the Bering west of the Pribilofs through
Wednesday.

&&

.MARINE (Days 3 through 5)...

...Bering Sea and Aleutian Coastal Waters...

Thursday the models have a weakening low near Bristol Bay/Eastern
Bering and a mature system near Kamchatka with a surface low
ranging from 971 mb - 975 mb. Friday this low is near Attu
Island/Shemya and the models bring it eastward. Expect gale force
winds to materialize near the Aleutians. Light to heavy freezing
spray is expected near Nunivak Island on Thursday and again on
Saturday.

...Gulf of Alaska...

A low will move into the region bringing widespread small crafts
and the potential for gale force winds. Given the long fetch
length, seas are expected to build to 20 to 25 feet on Thursday.
The rough seas will linger into Friday. Currently, the expectation
is that the seas will subside on Saturday but as the new model
runs become available that may change. Stay tuned.

&&

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

From the onset of this forecast period, the global models are not
in sync projecting the track and the intensity of a low near the
mainland and a second low near Kamchatka. The NCEP RMOP (National
Centers for Environmental Prediction Relative Measure Of
Predictability) displays large swaths of low confidence territory
from the Bering to the Gulf Of Alaska and over the mainland at
72hrs and beyond. However, a few items can be gleaned from the
models. Expect more cyclogenesis and unsettled weather for the
Bering and the Aleutians. For the southern tier of the mainland,
temperatures will be near or slightly above normal.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NPW 101 125.
MARINE...Gales 119 120 125 130-132 136-139 160 165 177-181 185 351 352
               411 412 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...BB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
MARINE/LONG TERM...PS