Small Craft Advisory 94, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
447 PM AKST Mon Jan 29 2018

.ANALYSIS AND UPPER LEVELS...
An upper level blocking ridge remains over the northwest Bering
today and is the main weather feature for the state. An upper
level tough stretches out of the Yukon Territory and into the
eastern Gulf of Alaska. this combination is causing strong upper
level northerly winds over Southwest Alaska with some of that
support extending into Southcentral Alaska as well.
The very tight pressure gradient at the surface combined with the
upper level support is the reason for the gusty winds in
Southcentral and Southwest Alaska (including the Alaska Peninsula).

&&

.MODEL DISCUSSION...
With the blocking ridge over the Bering Sea and eastern Russia
keeping the pattern stable, the models are all locked into the
same overall solution. A small difference that may make a
difference in winds over Southcentral Alaska Tuesday into Tuesday
night is associated with the track of a 500 mb low moving from the
Alcan border tonight to near Kodiak late Tuesday night. The GFS
and NAM both track this low over Prince William Sound while the
ECMWF moves it over Anchorage and Cook Inlet as it moves
southwestward. The difference this makes will be in the amount of
upper level support the winds have from northern Cook Inlet
through the Matanuska Valley with more upper level support with
the GFS/NAM solution.

&&

.AVIATION...
PANC...VFR conditions will persist through Tuesday. Gusty northerly
winds will also persist, though they are not expected to be quite
as strong tonight into tomorrow as they were overnight last
night.

&&
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
With low pressure to the south and high pressure continuing to
build in over the northern part of the state, outflow winds look
to continue through the early part of the week. However, the upper
level support has shifted somewhat to the west which will diminish
the winds from the highest amounts seen last night. On Tuesday,
an upper level low will move over the Gulf from the northeast
which will form a surface low that will track toward the western
Gulf Tuesday night. This will increase the pressure gradient
again which will reinforce the outflow winds for western portions
of Southcentral Alaska like the Matanuska Valley.

This setup will keep precip away from most of Southcentral Alaska
with the exception of Kodiak. As the low develops in the Gulf it
will bring a stream of moisture to the island bringing snow
Tuesday night into Wednesday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The forecast remains on track as no significant changes are
expected given this stagnant pattern. A shortwave will track
through the Bristol Bay area this evening and cross the Aleutian
range into the North Pacific tonight. Some localized gusty winds
will persist through thursday over a few spots where the
inversion breaks. Otherwise, expect dry conditions to persist
through Thursday given the offshore flow pattern. Although cold
temperatures will persist, wind speeds will remain light enough to
preclude any headline concerns.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
With the ridge of high pressure continuing to dominate much of the
region, the only real item of interest will be strong gap winds
along the Alaska Peninsula and far eastern Aleutians tonight as a
shortwave crosses the Aleutian Range into the north Pacific
tonight. While winds aloft remain strong with 850 mb winds of 40
to 50 knots seen in model forecasts, area soundings area showing
a strong inversion persisting. Thus, most of this energy won't be
realized. The exception to this being along and south of the
mountains along the chain/AKpen, where orographic lifting will
weaken the inversion along the higher elevations, with downward
momentum transfer being maximized south of these locations where
increased gravitational friction will give a boost to the wind
gust potential. As the shortwave moves away from the region late
tonight, winds will begin to subside, but remain gusty. With no
change in the synoptic pattern seen for several days, dry
conditions will prevail aside from a few hit and miss flurries.

&&

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

Beginning the long term forecast period Wednesday night, there
will be a rather stout high latitude omega block over Eastern
Siberia with an elongated trough stretching from the Eastern
Aleutians to the Canadian Maritime. A very stout arctic surface
high will be in place over eastern Alaska, with a continuation of
the current dry, cold offshore flow pattern. Precipitation will be
relegated to Kodiak Island, but it is expected to be all snow, and
there may be some decent accumulations, especially along the
eastern part of the island. With time, the omega block will shift
east over northwest Alaska which will effectively elongate and
shear the upper trough over Alaska. By late Friday into Saturday,
a North Pacific warm front will lift north into the Gulf of
Alaska, bringing much heavier precipitation to Kodiak Island (snow
changing to rain). This is where uncertainty grows rather quickly
among the global models. The GFS has been consistently progging
the front to reach the North Gulf Coast by Saturday while the
ECMWF and Canadian GDPS favor a slower progression given the
strength of the arctic high. In fact, the ECMWF never progresses
the front farther north than Kodiak, keeping all of mainland
Alaska and the coast dry. For now, an approach favoring the ECMWF
and the ECMWF ensemble is preferred. However, it is not out of the
question that the GFS verifies with warming temperatures by early
next week...and increasing chances for precipitation (favoring the
coast). Stay tuned...

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gales 127 128 130 139 150 155 180.

&&

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