Small Craft Advisory 725, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
429 PM AKDT Wed Sep 27 2017

.ANALYSIS AND UPPER LEVELS...
The upper level low south of Kodiak is cut off from the trough in
the Arctic which has allowed some upper level ridging over the
interior of the state. Zonal flow is over the Bering Sea with an
amplifying ridge near Kamchatka. The jet stream remains running
well south of the Aleutians from west to east and then rotating
around the southern periphery of the low into Southeast Alaska.
The main surface low is moving northward toward Kodiak Island and
will remain just east of the Island into Friday.
A surface ridge in the western Bering Sea and over the western
Aleutians will edge eastward the next few days keeping the
northerly flow over most of the Bering Sea for a few days.

&&

.MODEL DISCUSSION...
On the synoptic scale, the models are in good agreement into the
weekend and then some significant differences begin to emerge.
One short term detail that will have an effect of the western part
of the Gulf, including Kodiak Island, is the structure of the low
moving into the area. The GFS is consolidating the energy into
one distinct center with the ECMWF showing a more elongated
center. The ECMWF solution is supported by the NAM which shows a
two distinct centers for the low that match the overall shape the
ECMWF is showing. It is likely that the NAM is the most correct
solution with the resolution difference being the reason the EC is
elongated and not with two distinct centers. Where this may have
an impact on the Kodiak area is with the winds around the low and
whether or not there will be a short break in the rain overnight.

&&

.AVIATION...
PANC...VFR conditions will persist even with a little rain moving
into the area by this evening. Winds should turn southeast
Thursday afternoon and may get a bit gusty at that time as well.
It looks like the airport will be right on the edge of the higher
gust area as they come out of Turnagain Arm.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
With an occluded front in the Gulf of Alaska, a wet pattern is on
tap for this evening over Southcentral Alaska. Both the Kenai and
Middleton Island radars are pinging into precipitation, with the
best and most uniform bands materializing over Prince William
Sound. An inverted trough will barrel through the Kenai Peninsula
tonight increasing the pressure gradient forces over the region,
resulting in gusty winds through Turnagain Arm, the Knik River
Valley, and Copper River areas through Thursday. From this event
the lion's share of the QPF is expect east and southeast of
Anchorage where the moisture will get wrung out by the Chugach
Range. As time elapses, the surface low will slowly weaken and
drift southeastward which will give way to a drying trend.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Dry northerly flow will dominate much of southwest Alaska through
Friday. The exception will be a deformation zone forming over the
Aleutian and Alaska Ranges that will bring rain into Friday.
Ridging looks to build in over southwest Alaska also on Friday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Ridging over the western Bering will slowly track east into the
central Bering on Friday, extending over southwest Alaska as
well. This will keep northerly flow for most locations in the
Bering and Aleutians until the ridge axis moves overhead resulting
in light winds.

&&

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

It looks like a sunny weekend is on tap for much of the Alaska
mainland this weekend as high pressure builds across southern
Alaska from the eastern Bering Sea. In the meantime, a pattern
change will begin to take hold across the western Bering Sea as
the arctic jet begins to strengthen as cold air builds over
eastern Russia. A the jet strengthens, the upper level pattern
will become more "zonal" and allow for multiple disturbances to
track off the coast of Russia and into the Bering Sea and
ultimately into Southwest Alaska. This pattern change should also
keep the subtropical jet well south of Alaska and Alaskan waters
which means that the warm and moist air that brought rainfall much
of the summer/fall will now be cut off from Alaska. Models are
struggling with timing, placement and intensity of features moving
off the coast of Russia but a very active pattern looks likely by
Monday of next week. Looking back at the nice weekend,
temperatures will likely be near or below freezing across most
inland locations while high temperatures climb into the upper 40s
to upper 50s.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...None.

&&

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