Gale Warning 220, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
522 PM AKDT Tue Mar 26 2019

.ANALYSIS AND UPPER LEVELS...
The old Bering Sea storm has moved into eastern Russia and is
continuing to weaken this afternoon. This leaves a fairly tight
southerly pressure gradient over the Bering Sea and a washed out
front over southwest mainland Alaska. An upper level ridge is
building over Southcentral Alaska today with a jet streak around
115 kt at 250 mb over western Alaska. This ridge will give way
briefly to a short wave on Thursday and then another ridge will
build into mainland Alaska from the Southwest after that.
Therefore, this current ridge is not the one that will persist
that will be referenced later in the discussion.

&&

.MODEL DISCUSSION...
Models remain in very good agreement with developing a blocking
ridge over the state late this week and keeping the low track in
the western Bering Sea. The biggest item to note in regards to the
model is that there has been resolution of the discrepancy in the
short wave over southwest mainland Alaska on Wednesday night and
Thursday. Yesterday, the GFS model was indicating the chance of
precipitation over Southwest mainland Alaska, but the NAM was
pushing to 500 mb ridge axis over that same area keeping it dry.
Today, the NAM has ceded that position to the GFS and both sow a
stronger short wave that has the potential for some precipitation
in Southwest mainland and some clouds spilling into Southcentral
as well.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

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

A high amplitude upper ridge is continuing to build over the
state resulting in the warm and nice weather across the region.
It is so warm and nice that a weak sea breeze developed in Homer
this afternoon, and Seward and Valdez both pushed above 50
degrees. Some mid level clouds will move in tonight, but more
clearing should develop and result in another nice day Wednesday.

The next weak shortwave trough will move east Thursday bringing
increasing mid level clouds and threats for snow near the Alaska
Range, otherwise, expect continued dry weather for inland areas.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
(Tonight through Friday afternoon)

A ridge over the eastern Bering will provide generally clear and
calm conditions for Southwest on Wednesday. Fog and low level
stratus are likely around the Bristol Bay area overnight tonight
through early Wednesday morning thanks to weak winds and ample
moisture. By Wednesday evening, an upper level trough will lift
over Southwest, providing enough of a disturbance to generate
precipitation over the Kuskokwim Delta Coast. As the upper level
trough tracks eastward, precipitation will eventually develop
across much of the Kuskokwim Valley and greater Bristol Bay area for
Thursday morning. Temperatures at this time are expected to be
cold enough for snow, though a rain/snow mix is possible.
Precipitation will gradually taper from west to east Thursday
afternoon, and a surface ridge will return over Southwest for
Friday.

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
(Tonight through Friday afternoon)

Southwesterly flow will persist over the Bering through the
evening. A weak upper level shortwave will lift over the Pribilofs
tonight bringing a chance of snow showers and a generally showery
regime over the northwestern Bering will eventually diminish as a
surface ridge builds over the central Bering for Wednesday
morning.

By Wednesday afternoon, a front associated with a Kamchatka low
lifts over the western Aleutians bringing another round of warm
southerly flow. The front is well-occluded and while winds will
start as gale- force, they will quickly weaken as the front moves
over the central Bering for Thursday morning. By the afternoon,
an embedded wave will bring another swath of gale-force winds just
west of Adak. This trend of southerly flow will continue over the
western Aleutians through Friday afternoon as an upper level jet
supports an embedded surface wave over the Rat Islands and Adak.

&&

.MARINE (Days 3 through 5/Friday through Sunday)...
There is high confidence in benign conditions from Southwest
Alaska coastal waters to the Gulf of Alaska, with a strong upper
level ridge sitting overhead. For the rest of the Bering Sea and
Aleutian chain, confidence is fairly high in southerly gales
on Friday. As we head through the weekend into early next week,
confidence drops with track of another deep storm. Guidance does
indicate the center of the storm will remain south of the Aleutian
Chain. Based on this, would expect additional periods of gale
force winds along the Aleutians and southern Bering Sea.

&&

.LONG TERM FORECAST (Days 4 through 7/Saturday through Tuesday)...
A strong closed blocking upper level ridge will set up shop
directly overhead of mainland Alaska. Models attempt to slowly
weaken the ridge early next week, but carry a healthy amount of
skepticism since models bias is to break these ridges down too
quickly. In any case, there is high confidence that this ridge
will provide dry weather and continued above normal temperatures
for Southwest and Southcentral Alaska through at least early next
week. With strengthening inversions underneath the upper ridge,
fog will be a threat. Will have to wait until we get closer in
time to determine whether the local scale environment favors fog
development.

More active weather will persist upstream of the ridge, primarily
across the western Bering and Aleutians. A deep trough and strong
subtropical jet over the west Pacific will support continued
development of deep lows over the northwest Pacific. These systems
will weaken as they approach the western Aleutians. While there is
some uncertainty in handling of specific storms, there is high
confidence in the general weather. Largely, it will be a
continuation of what we are seeing in the short-term, with periods
of gale force winds and rain.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales 176-178 411.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KO
MARINE/LONG TERM...SEB