Small Craft Advisory 179, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
447 PM AKST Mon Feb 27 2017

.ANALYSIS AND UPPER LEVELS...
An upper level trough is currently diving across the southwest
mainland this morning. Ahead of this trough, light snow showers
have been occurring across portions of Bristol Bay and the
Kuskokwim Valley. This trough has also supported light snow across
the Anchorage Bowl and northern Kenai Peninsula this morning and
afternoon. Strong cold air advection behind the trough is
supporting showers along the northern AKPEN along with gusty
northerly winds. Meanwhile an amplified ridge is intensifying
across the western Bering Sea and supporting generally clear skies
north of the Aleutian Islands.

&&

.MODEL DISCUSSION...
Models have had a difficult time capturing the precipitation that
developed over the Anchorage Bowl this morning. The NAM did the
best job of capturing the precipitation development and intensity,
but was several hours late. For the short term, the NAM was
favored for Southcentral for its ability to capture downslope
winds well. Models are in good enough synoptic agreement across
the Bering and Southwest mainland and a blend of models was
favored.

&&

.AVIATION...The current low stratus deck is expected to slowly
lift during the evening hours and approach VFR by later this
evening. Expect northwesterly flow to increase in speed during
the overnight hours.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A forthcoming pattern change will bring Arctic air back down into
the area. A weak disturbance that brought light snow to the Cook
Inlet region is the leading edge of digging upper-level trough
that will usher in a new air mass for the foreseeable future.
Some low and mid-level clouds will linger overnight and into the
morning hours but generally clouds will be going away in favor of
clear sky sooner rather than later. The influx of cold air along
with low pressure developing in the Gulf will ratchet up gap winds
in favored areas along the north Gulf coast. Seward, Whitter, and
Valdez will all see gusts around 50 mph in the next day or two,
which will keep their temperatures inflated near current levels
while the remainder of the mainland goes into the deep freeze.
The light northerly winds developing tonight, combined with lingering
clouds, will keep the overnight lows from falling too far tonight.
However, the air mass will not be denied, low temperatures by
Tuesday night will likely fall to zero or below in most places
around Southcentral AK.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Showers will taper off tonight as dry air follows behind the
shortwave digging south into the North Pacific. Then cold air
and clear skies will be ushered in over the area Tuesday and
Wednesday from the north as high pressure settles in over the
Bering. The high pressure will also bring northerly winds to
southwest Alaska.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
High pressure will settle in over the central Bering by Tuesday
morning bringing northerly flow over the eastern Bering and
southerly flow over the western Bering. The ridging will help
to stall a front that is approaching the Western Aleutians from
the west and leave a stationary boundary over the islands into
Wednesday. This system looks to be bringing up enough warm air
to remain as mostly rain.

&&

.LONG TERM FORECAST (Days 3 through 7)...
By the beginning of the extended forecast period Thursday much of
the region will have already undergone a transition in the overall
pattern, with a broad upper level trough over much of the Mainland
and Gulf, and strong ridging out west over the Bering Sea and
Aleutians. This general setup will persist through early next
week, which will consist of colder air filtering down from the
arctic and strong outflow winds over parts of the Southern Mainland.
Models remain in good agreement with the overall pattern into the
weekend. As expected though, there is more uncertainty with
regards to the finer details, especially with respect to low
amplitude shortwave troughs diving south toward the Gulf of Alaska
coast Friday through Monday.

All three major global deterministic models, (the ECMWF, Canadian
GDPS, and GFS) along with their respective ensembles, are also
depicting a rather significant bora polar air outbreak across
much of Mainland Alaska. There is potential of seeing 850 hpa
temperatures reaching as low as -20C to -30C across the Southern
Mainland with cold offshore flow along the coast. The March sun
should moderate some of the cold air at the surface, but the
reality of this situation is it will be quite cold and well below
average for the next 7-9 days, dominated by dry offshore flow and
cold interior temperatures.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Heavy Freezing Spray Warning 129 130 138 139 141 150 160
                                      165 180 185.
	     Storm Warning 130 131.
 		 Gale Warning 120 121 127 128 129 132 136 138 139 150 175
                      176 177 178.

&&

SYNOPSIS AND MODEL DISCUSSION...EN
SOUTHCENTRAL ALASKA...MTL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...TP