Small Craft Advisory 206, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
434 PM AKST Fri Mar 9 2018

.ANALYSIS AND UPPER LEVELS...
A broad trough with multiple embedded vortices is the main upper
level feature today. A weakening storm moving north across the
Alaska Peninsula is the key feature. Satellite imagery shows
widespread open cell cumulus, indicative of showery unstable
conditions, extending from south of the Alaska Peninsula to across
much of the central and eastern Gulf of Alaska. Lightning strikes
were registered over the Gulf and along the Gulf coast.
Widespread snow showers were also reported over the North Gulf
Coast and over the Kenai Peninsula. Strong east winds with low
visibilities in blowing snow continued across Turnagain Arm and
through Portage Valley into the afternoon hours. Out west, strong
and gusty northerly winds dominate much of the central and eastern
Bering Sea, Aleutians, and Alaska Peninsula. Storm force and
locally higher gusts were also observed through gaps in the
southern Alaska Peninsula. Widespread snow showers were also
observed over much of the central and eastern Bering Sea.

&&

.MODEL DISCUSSION...
Models are adequately handling the weakening storm over the Kenai
Peninsula and next front heading east across the Bering Sea this
weekend. Model consensus is very poor with next triple point
heading north across the Gulf this Saturday and Sunday. Generally
used a weakened version of the 12z NAM.

&&

.AVIATION...
PANC...Generally VFR conditions. Gusty southeast winds across the
airport complex this evening should hold until about midnight
before diminishing.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The strong storm that impacted the entire region yesterday is now
in the weakening phase, and is in the process of crossing over the
Kenai Mountains into the Cook Inlet area. Strong winds and heavy
snow are continuing along the eastern Kenai Peninsula, and can be
expected to continue through the night with significant additional
snow accumulations. Another impact as this storm is crossing into
Cook Inlet is the redevelopment of heavy snow around the Kachemak
Bay/Homer area. Gusty southwest winds have also developed, and
several hours of heavy snow and blowing snow can be expected
before conditions improve by later this evening. Meanwhile,
significant instability and heavy snow showers will continue along
the rest of the north Gulf Coast including Valdez and Cordova
tonight. In fact, the atmosphere is so unstable that a few
thunderstorms are likely along the coast through tomorrow morning.

This storm will slowly weaken in place across the western Gulf
through the day Saturday, so more snow showers can be expected,
especially over the coastal areas. By Saturday night, showers will
diminish as a whole new storm starts to move into the area from
the southeast. The track and timing of this storm is still very
much up in the air, but it does look like the Prince William Sound
and Copper River Basin areas will see more snow move in during
the day Sunday. The western edge of the snow is uncertain, but it
can't be ruled out that it stretches all the way westward to the
Seward and Anchorage areas. Stay tuned to future forecast updates.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The mainland lies right on the edge of the decaying system over
Southcentral Alaska, which will lead to lingering snow overnight
tonight, mainly for Bristol Bay and the Kuskokwim Valley. The
combination of freshly fallen snow from the last front and
stronger winds on the backside of the low pressure system are
bringing reduced visibility in blowing snow to the Kuskokwim
Delta Coast. A blowing snow advisory has been issued. Conditions
should stay around one-half mile visibility or less until early
Saturday morning when the winds begin to lighten up.

As the low in the Gulf pulls away, winds will slacken and upper
level clouds will clear. These conditions combined with recent
low-level moisture, and a touch of return flow (warm advection)
should lead to widespread stratus/fog over at least Bristol Bay,
if not the Kuskokwim Valley on Sunday morning.

The next frontal boundary rolls in on Sunday, and should bring
widespread accumulating snow to much of the mainland. At this
point it doesn't look like much, especially compared to the last
system, but should be high probability.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Widespread cold advection snow showers will continue for the
eastern Bering Sea through Saturday morning. The showers will be
heavy at times, and combined with the strong wind, will drastically
reduce visibility for short periods of time, mainly along the
Alaska Peninsula.

The next warm front is already making its way into the western
Bering Sea. The front will move west to east across the Bering,
with a robust warm sector, bringing snow then rain to the
western/central Aleutians. There is still some question about how
far east the warmest air makes it, but the current forecast has
both the Pribilof Islands and Alaska Peninsula turning briefly to
rain on Sunday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long term forecast begins Monday with a deep but narrow upper
level long wave trough bisecting mainland Alaska and extending
south to nearly 30N. A surface low will move from the Northern
Gulf into Prince William Sound bringing another round of snow to
coastal areas and the mountains, though the inland areas west of
the Kenai and Chugach Mountains look to remain mostly snow free as
the bulk of the moisture and energy should remain far enough east.

A progressive pattern will continue across the region as we head
into the middle of next week as a strong westerly jet moves over
the Aleutians and pinches off the upper level low well to the
south of our area. Temporary ridging will build in over the
southern mainland Tuesday and Wednesday morning bringing a short
break in the stormy pattern before another trough digs in across
the Eastern Bering, spinning up another low that looks to move
across Western Alaska and eventually Southcentral by Thursday. The
models begin to diverge some at this point with the track of the
low center, but all agree that a decent amount of moisture will be
associated with this system and will be aided by a strong
southerly upper level jet pumping moisture in from the North
Pacific. This storm also looks to be a bit warmer than the
previous ones we've seen the past couple of weeks, meaning
precipitation types could be challenging with rain possibly mixing
in with snow at sea level locations. Stay tuned as details become
clearer regarding this system next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Warning 125. Winter Weather Advisory 155.
MARINE...Gale Warning 160 165 170 171 172 173 174 175 176 177 178
179 180 181.
Heavy Freezing Spray Warning 160 180 181 185.

&&

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