Brisk Wind Advisory 46, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
436 AM AKST Wed Mar 4 2020

.ANALYSIS AND UPPER LEVELS...

There is a high amplitude upper level ridge over the central and
western Bering. A sharp north to south oriented trough is over
eastern Alaska, slowly moving southeastward. Strong northerly flow
aloft is between these features, from southwest Alaska through
the eastern Bering and Aleutians. At the surface, there is a low
centered just south of Prince William Sound with a high over the
central Bering. Strong gap winds are occurring from the northern
Gulf through the eastern Aleutians. Satellite imagery confirms
cold advection is making its way through gaps in the eastern
Aleutians and Alaska Peninsula, as cloud streets are visible south
of the Chain. Scatterometer winds show gales with storm force
gusts south of the Peninsula and, earlier, showed storms across
the Barren Islands. Some showers associated with the low south of
Prince William Sound are occurring around the Sound and into the
Copper River Valley. There are also some showers over the eastern
Aleutians associated with the unstable northerly flow.

&&

.MODEL DISCUSSION...

The numerical guidance is in rather good agreement through
Thursday afternoon. The main forecast challenge will be winds
from cold advection and winds through bays and passes along the
eastern Aleutians, Alaska Peninsula, Gulf coast and Prince William
Sound. Forecast confidence is high.

&&

.AVIATION...

PANC...VFR conditions are most likely. Northerly winds could be
gusty at times.

&&

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

Outflow and local gap winds will be the main weather concern
through Thursday. An upper low moves slowly east across the Gulf
today then weakens and drifts south this evening as upper ridging
builds in from the west. A northerly jet on the backside of the
trough moves over Southcentral this evening. At the surface, cold
air continues to spill into Southcentral and through gaps in the
Aleutian Range which keeps a fairly strong thermal gradient
between the marine and continental air masses. This, combined
with building pressure gradients and increasingly favorable
northerly flow aloft, will strengthen outflow and gap winds this
afternoon into Thursday. The strongest winds will likely be along
the North Gulf Coast where winds will likely hit warning levels by
early this evening in the Valdez zone and through the Copper
River Delta. Winds will diminish in many areas later Thursday as
pressure gradients relax and the upper ridge moves over
Southcentral and terminates upper wind support.

Cooling temperatures and gusty northeast winds will likely keep
the potential for a wind chill advisory over the northern Susitna
Valley through tonight.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
(Today through Thursday evening)

A series of disturbances aloft will dive south, crossing the lower
Kuskokwim Delta, Bristol Bay, and the Alaska Peninsula (AKPEN)
through this evening. Here, areas of light snow will continue to
affect these locations through the late afternoon or early
evening. A ridge of high pressure building into the central Bering
on Wednesday will put an end to these after that.

Further east across the interior, this region will be sandwiched
between the advancing high pressure to the west, and a low near
Prince William Sound. As a result, breezy northerly winds will
persist through the afternoon, with a few areas of blowing snow
possible. These winds should diminish by this evening, with mainly
clear and cold conditions persisting.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
(Today through Thursday evening)

A few disturbances pass overhead, across the eastern Bering and
AKPEN, bringing a few snow showers to the region. These showers
become more robust, though, as they pass over ice free waters.
A respectable ocean delta-t spread (the difference in temperatures
at 850 mb, or roughly 4500 feet, and the ocean water
temperatures) are large enough for some weak instability to
develop. These "heavier" snow showers also get a boost from
orographic lifting as they move ashore across the northern
portions of the Peninsula, briefly reducing visibilities at
times. This is expected to continue through the afternoon, before
diminishing by late evening.

South of the AKPEN, downsloping winds off the Peninsula will
accelerate as gravity plays a role: helping the air to sink more
rapidly while increasing in speed. These increased winds will also
get funneled through bays and passes, where a few hurricane force
wind gusts remain possible today. High pressure situated to the
west and a low in the Gulf is also creating a tight pressure
gradient, helping augment this process. However, the Gulf low will
move east and weaken as the high moves into the central Bering
tonight and Wednesday, allowing winds to subside.

Further west, the main item of interest will be a low pressure
system currently southwest of Shemya. This low will continue its
approach towards the western Aleutians, with its associated
surface front moving into that region Wednesday evening through
Thursday morning. Sustained gales will precede this front, while
also being accompanied by a steady band of precipitation. Here, a
few storm force gusts are a distinct possibility. The low reaches
the western Bering by Thursday afternoon, with the front
stretching from the Pribilof Islands through the eastern
Aleutians. Although it'll be in a weakening state, both the low
and the front, some sustained gales remain possible.

&&

.MARINE (Days 3 through 5)...

The most active pattern will be over the Bering on Friday as a 995
mb low, just west of Saint Paul, slowly weakens on a southeasterly
track. This is followed by the next North Pacific low Friday
night which continues on a northeasterly track nearing the
Pribilof Islands late Sunday. Both of these systems are expected
to bring small craft winds with rain along the southern waters and
snow from the Pribilofs north. There is some uncertainty on wind
speeds with the second system; some adjustments may be needed to
increase winds around the core of low.

&&

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

Saturday through the beginning of next week, a wetter and warmer
pattern is expected as two low pressure systems move from west to
east from the Bering. The first low pressure system over the
central Bering on Saturday morning tracks quickly across the
southern mainland bringing the first round of snow. Temperatures
moderate into the 20s to lowers 30s with the frontal passage,
keeping precipitation snow for the southern mainland. Southern
Bering and Gulf locations, including the Alaska Peninsula, Kodiak
Island and southern tip of the Kenai are expected to warm enough
to change snow over to rain. The second system follows quickly
behind the Saturday storm, tracking across the Bering Saturday
night. This storm will likely pull a warmer maritime air mass
further north Sunday into Monday across Bristol Bay. There is high
uncertainty on the evolution of the second storm with models
varying on the track and strength of this system from run to run.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...

PUBLIC...Blizzard Warning 131.
		 High Wind Warning 131.
		 Wind Chill Advisory 145.

MARINE...Storm Warning 127 130-132 150.
		 Gale Warning 119-121 126 128 129 136-138 155 165 170
		 172-178 352 411-414.
		 Heavy Freezing Spray Warning 119-139 141 150 165 179
		 180 414.

FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...CRK
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
MARINE/LONG TERM...KH