Small Craft Advisory 110, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
634 AM AKST Sat Feb 3 2018

.ANALYSIS AND UPPER LEVELS...

The upper level col centered right over Southcentral is
diminishing this morning as ridging begins to take over. A broad
upper level low over much of the Bering continues to keep
conditions unsettled over the southern Gulf and it is extending
westward through much of the Aleutians. It is in this area where
the cold air over Alaska and warmer air meet, resulting in the
precipitation.

Across Southcentral, cold and quiet conditions persist this
morning. The only weather hazard threats, strong winds and
marginally cold wind chills, are abating this morning. Over the
Matanuska Valley, where the wind has been nearly non-stop for over
a week, the winds are beginning to taper down. As long as very
cold air over the Copper River Basin remains present, which is
most certainly still occurring, then a prolonged period without
wind is unlikely. However, with the northeasterly flow abating in
the upper levels, there will be less forcing to help push that
cold air down the valley. A similar situation is also present
through Thompson Pass, Valdez, and the Copper River Delta with the
forcing diminishing with time.

&&

.MODEL DISCUSSION...

The models all remain in good agreement through the short term,
though by the start of the workweek, with the weather pattern
turning to lows moving in from the data-sparse Pacific, model
agreement and forecast confidence rapidly decrease. The primary
forecast challenges remain the extent of precipitation and
visibility reduction issues from Kodiak westward across the
Aleutians, and the gap winds ongoing over portions of mainland
Alaska.

As far as the next front moving north on Monday goes, the
GFS remains by far the fastest of the models with moving
precipitation northward first through Kodiak, then north along the
Gulf Coast. It's solution was largely thrown out as this pattern
has been very persistent and the slower NAM/EC solution looks more
reasonable.

&&

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

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The longwave pattern features a dome of high pressure over
Northeast Russia with ridging that has moved south of the Brooks
Range and a second amplified ridge axis over the East Pacific.
There is a low south of the Western Aleutians that has ejected a
series of shortwaves towards Kodiak. Over the Anchorage Metro Area
and the Mat-Su Valleys, expect more dry conditions with brisk
mornings and afternoon highs near the 20F benchmark. With the
ridge influencing the domain, the pressure gradient is re-
orienting. The winds near Palmer and Wasilla will remain gusty
today albeit less harsh than days earlier. The worst is over for
this week-long wind event. There is still a pool of cold air over
the Copper River Basin, but there have been enough shifts in the
synoptic pattern to justify more optimistic conditions in the
Matanuska Valley. Sensible weather-wise, Kodiak will be the most
active region of the AOR this forecast period as the next wave of
moisture continues to march towards the island. There is some
question as to whether this next system will start as a rain-snow
mix or start as snow. There is high confidence in a QPF event for
Kodiak. However, a skosh lower confidence level on mode of
precipitation especially for the city of Kodiak and some of the
coastal locations. For the higher elevations of Kodiak Island such
Erskine Mt, it's a slam dunk for a snow event. Even if
precipitation is all snow at the city of Kodiak, the warm
temperatures at the surface will limit snowfall accumulations.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
Dry conditions, generally sunny skies, and offshore flow will
continue this weekend as a gale force front over the Eastern
Bering rides along high pressure that will persist over the
Mainland. This will bring gusty northerly winds, especially to
Bristol Bay today, but otherwise very little impact is expected to
the region from this front. Instead, clear skies and light winds
will allow for temperatures to fall into the 20's to below zero
in the Kuskokwim Valley again tonight, with single digits further
downstream in the delta.

Warmer temperatures and chances for snow are then expected to
return to the region by late Monday as the Mainland ridging
retreats far enough north to allow a gale force front to move
inland. This front will bring temperatures above freezing along
with gusty north-east winds and a rain/snow mix to Bristol Bay
through Monday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
Widespread rain showers along with gusty east winds will continue
over most of the Bering/Aleutians today as an elongated front
slowly diminishes along the edge of the Mainland ridge. After this
front moves out of the Bering on Sunday, the focus will then
quickly shift to another gale force complex low that will spread
rain/wet snow into the Eastern Aleutians and AKpen into Monday.
With weakened ridging over the Mainland, this low will be allowed
to take a much more northerly track into the Bering. This will
allow for warmer temperatures, a shift to southerly flow, and an
end to the persistent northerly cold air advection that will
persist through early next week.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The extended portion of the forecast beginning Sunday night will
feature the blocking high currently over the southern Chukchi Sea
shifting eastward to mainland Alaska and undergoing a gradual
weakening trend. This subtle pattern shift will coincide with a
frontal system approaching the Gulf on Monday. Most of the
guidance at this time suggests that the influence of the high
pressure to the north should be enough to weaken the approaching
front and divert the bulk of the energy from this system off to
the east, keeping the next precipitation threat limited to coastal
locations as inland Southcentral remains dry. The dry pattern
then looks to continue for much of next week as some semblance of
upper level ridging remains over mainland Alaska through Friday
despite model differences regarding the exact placement. This will
also allow temperatures to gradually moderate during the week,
although this trend may be a little slower to materialize over
inland valleys as steep surface inversions remain in place.
Meanwhile, the eastward shift of the blocking high will allow
broad troughing to be established over the Bering Sea by early
next week. This will usher in a more active pattern as various
disturbances rotate through from the north Pacific bringing
periodic threats for precipitation and stronger winds.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale Warning: 120 130 131 132 138 150 155 160 165 170 179
                       180 351 352 413 414.
 Heavy Freezing Spray: 121 126 127 128 139 160 180 185 414.

&&

SYNOPSIS AND MODEL DISCUSSION...JPW
SOUTHCENTRAL ALASKA...PJS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK
LONG TERM...CB