Small Craft Advisory 224, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
350 PM AKDT Fri Mar 16 2018

.ANALYSIS AND UPPER LEVELS...
The remnants of a frontal boundary extends from a low near Cape
Newenham to across the Southwest Mainland to over northern
Southcentral. Areas of snow and blowing snow were evident over
the Delta, snow over the lower Kuskokwim Valley, with a mix over
Bristol Bay. Broad southwesterly flow in the mid to upper levels
continued snow over much of the Susitna Valley and along the
Talkeetna Mountains. The low near the eastern Aleutians kept temps
on the warm side with rain along the eastern Aleutians/western Ak
Peninsula. While to the north gusty northeast winds with snow
continue across the Pribilofs. A low and associated frontal
boundary brought gale force southerly winds and rain to the
western Aleutians.

&&

.MODEL DISCUSSION...
Models overall are in fairly good agreement through Sunday
afternoon. The trend has been to slow down the progression of the
front moving east across the Bering Sea this weekend. The main
impact across Southcentral is to hold the heavier snow potential
for the Susitna Valley and Talkeetna Mountains until Sunday night.

&&

.AVIATION...
PANC...Gusty south winds will end this evening. Lower clouds
and/or visibilities are possible Saturday...mainly in the morning.

&&

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

A bit of lingering snow in the northern Susitna Valley and Hatcher
pass are all that remain of the storm that moved through yesterday.
Showers will continue to diminish in coverage and intensity
throughout the evening, as weak ridging builds into the area from
the south. This ridging, combined with neutral temperature
advection and residual low-level moisture, means it is probably
going to be hard to get rid of the clouds around Cook Inlet,
though. In fact, patchy areas of fog can't be ruled out. Saturday
will be a pretty benign day, with some breaks of sun possible by
afternoon and mild temperatures near 40. By Sunday, however,
another storm starts to move towards the area with showers
increasingly likely throughout the day and more widespread mixed
precipitation possible for the Monday morning start of the work
week. The only places that will likely remain cold enough for all
snow are Hatcher Pass and the northern Susitna Valley. Stay tuned
to future forecast updates.

&&

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

The low now near Kuskokwim Bay and the associated front inland
along the Kuskokwim River Valley will continue north as it weakens
tonight. The upper level ridging briefly pushes in from the Gulf
of Alaska and the flow behind the front will remain southerly,
helping to keep the moist onshore flow in place and increasing the
chance for areas of fog. A large strong low anchored over the
northwest Bering Sea will swing a front across the Bering Sea to
the Bering Sea coast Saturday morning/afternoon bringing another
shot of precipitation to southwest Alaska overnight and tomorrow
morning. The upper level flow after this front moves inland and
dissipates will be out of the southwest, thus expect a
continuation of showery weather through the weekend over
southwest Alaska.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

A low over Unalaska will weaken into a trough as it slides off to
the southeast. The front associated with the low anchored over
the northwest Bering Sea will push into the eastern Aleutians
overnight then to the Alaska Peninsula area Saturday and Sunday.
Ample warm advection in advance of the front will keep all
precipitation for the Central and eastern Aleutians to the Alaska
Peninsula predominantly liquid.

Further west, the low now near Shemya moves to the northwest
Bering sea this evening. The associated front from the low through
the central Aleutians rapidly moves east across the Bering Sea
and Aleutians. The typical cold advection will occur post
frontally resulting in the gusty west winds along the western to
Central Aleutians. A secondary wrapped occlusion sweeps into the
western Aleutians late tonight bringing another shot of snow and
blowing snow to the Shemya area. Another storm will be moving into
the southern Kamchatka Peninsula area late Sunday. The warm front
will clip the western Aleutians bringing with it a shot of snow.
Between this low and the remnants of the previous front high
pressure moves over the Aleutians with a ridge to Bristol Bay.

&&

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

The mid/long term forecast begins Monday with an upper level
trough and associated surface low situated over the NW Bering
with a front extending out from the parent low and moving east
into Southcentral. Strong SW flow aloft will push moisture up the
Cook Inlet favoring the Susitna Valley and surrounding mountain
ranges with precipitation again. Warm air ahead of this storm
system will lead to a mix of precipitation types as it crosses the
southern mainland Monday, with snow briefly mixing in later in
the day as cold air advects in behind the departing front before
the precipitation shuts off.

In the wake of this system, a digging trough moving out of Asia
will lead to rapid building of a ridge over the Bering Sea Tuesday
through Wednesday. This will usher dry Arctic air from Siberia
southward across mainland Alaska and into the Gulf, leading to
below average temperatures and strong winds through the usual
terrain gaps along the Gulf coast and across the open waters of
the Gulf. Depending on the amount of cold air advection moving
into the interior, hurricane force gusts are not out of the
question through the typical wind funneled areas, including
Thompson Pass and Valdez, Tuesday through Thursday.  Models
diverge on whether this blocking ridge holds in place through the
end of next week or breaks down allowing the storm track to
meander back east into Southcentral again. Regardless, all models
show ridging and drier conditions through at least Friday of next
week over the eastern two thirds of mainland Alaska

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 178 185. Heavy Freezing Spray 181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...BC
SOUTHCENTRAL ALASKA...AMD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SA
LONG TERM...KVP