Small Craft Advisory 225, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
454 AM AKDT Wed Mar 15 2017

.ANALYSIS AND UPPER LEVELS...
A highly amplified pattern remains locked in place over the region
this morning, with a longwave trough spanning from the North Pole
across the mainland and Gulf of Alaska while a stout upper level
ridge continues to dominate the Bering Sea. This means more of the
same in terms of sensible weather as clear, cold, and windy
conditions persist across the bulk of the southern mainland. Winds
are following a familiar diurnal trend to the past few days, with
some of the gustiness subsiding overnight but poised to return
during the afternoon as daytime heating helps some of the stronger
winds to mix down from aloft. Strong gap winds are also present
along the Pacific side of the Alaska Peninsula beneath a 100+ knot
jet streak helping to dig the mainland trough. These winds are
poised to be enhanced further today by the latest and most potent
in a series of arctic shortwaves diving down the spine of the
Alaska/Aleutian Ranges. A broad low spinning over the gulf is
beginning to spread scattered snow showers over portions of the
coast including Cordova as the associated moisture finally begins
to overcome the copious amounts of dry air in place at the
surface given the recent pattern.

&&

.MODEL DISCUSSION...
Gap winds and localized gusts are once again the primary forecast
challenge today as the persistent longwave pattern promotes good
synoptic agreement amongst the models. The morning forecast
package continues to utilize Hi-Res NAM guidance to better capture
these features.

&&

.AVIATION...
PANC...VFR conditions and northerly winds will continue through
Thursday morning, with gustiness once again trending upward
during the afternoon owing to increased mixing associated with
daytime heating.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Expect one more day of widespread gusty winds driven by arctic
air over Southcentral and tight pressure gradients. Winds will
strengthen through the day across southern Cook Inlet, the
western Gulf, and Kodiak Island as a strong vorticity maximum
moves through aloft helping to drive arctic air southward through
this region. Although the more northerly direction of flow is not
ideal for gap winds on the west side of Shelikof Strait, there is
certainly enough pressure gradient to support northwesterly gap
winds. Also expect some transfer of very strong winds aloft as
the vort-max moves through, so have upped gusts to hurricane
force.

Meanwhile, a surface low crossing the northern Gulf will spread
some snow showers across the Prince William Sound area and
possibly northward into portions of the Copper River Basin.
However, with the strong offshore flow maintaining a dry boundary
layer in most areas expect little or no accumulation. Additional
lows will rotate around the Gulf, but it looks like they will take
a further south track.

Winds will finally begin to diminish across the region Thursday
through Thursday night as the low complex over the Gulf sinks
south and eastward. With less and less wind each night and a very
cold air mass in place expect a downward trend in temperatures.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Cold advection will be felt a little more today as a disturbance
drags down the brunt of the arctic air from the interior. Gusty
northerly winds will increase today, peaking in the
evening/overnight hours before slowly tapering off through
Thursday. Expect gusts to get in to the 40 mph range, making for
decently cold wind chill values, but not to advisory level. Late
Thursday night a weak disturbance/front from the northern Bering
will possibly bring some light snow to the Kuskokwim Delta. On
Friday, high pressure slides toward the mainland from the Bering
Sea giving a reprieve from the wind.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
High pressure sits over the central Bering, separating two
synoptic weather regimes. To the west, southeasterly flow with a
weak disturbance passing today, followed by a stronger front and
rain late Thursday. To the east, cold northerly flow promoting
snow showers toward the Alaska Peninsula. This pattern holds
through Thursday when the high begins to slide eastward toward the
mainland.

&&

.LONG TERM FORECAST (Days 3 through 7)...
A front will affect the western and central Aleutians through the
weekend with small craft and gale force winds. This front will
also be associated with periods of rain and snow. By early next
week high pressure will build south across the Bering with a
drying trend for most of the Bering and Aleutians.

Southwest AK will be cool and dry through Tue, except for a few
snow showers affecting the Kuskokwim Delta beginning on Fri.
Gusty northerly winds through the Aleutian Range will diminish on
Fri.

Low pressure rotating around the Gulf of AK, combined with high
pressure over the mainland, will bring periods of windy
conditions to channeled terrain of southcentral AK through Fri.
Impulses moving around the Gulf low will then bring some snow to
the north Gulf coast on Sat that has a chance of moving inland on
Sun. Although models are starting to indicate this inland snow,
confidence remains fairly low. The trajectory of the low moving
through the gulf, and associated impulses producing precipitation,
are difficult to pinpoint and will be watched closely during the
next few days.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None
MARINE...Gale Warning 119 120 121 126 127 128 130 131 132 136 137
					  138 139 140 150 155 177 178
		 Heavy Freezing Spray 121 130 131 132 136 137 138 139 141
							  150 165

&&

SYNOPSIS AND MODEL DISCUSSION...CB
AVIATION...CB
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MTL
LONG TERM...DS