Small Craft Advisory 305, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
505 PM AKDT Fri Apr 19 2019

.ANALYSIS AND UPPER LEVELS...

Broad cyclonic flow continues across mainland Alaska as a fairly persistent
upper low center continues over the Southwest mainland. Cooling associated with
this feature was evident on soundings across the mainland with
850 mb temperatures dropping into -10s(C) over the Southwest and
-8(C) over Anchorage.

At the surface, weak low pressure dominates much of the Southwest mainland
to Southcentral. Unstable conditions with cold air moving in aloft brought
fairly convective showers (mainly snow) to the Gulf of Alaska and
coastal Southcentral. The heavy band of snow which brought
accumulating snow from Western Prince William Sound to the
Anchorage Bowl has narrowed and is lifting north with the upper
trough. Pressure rises on the backside of the surface trough
brought very gusty south winds across the Copper River Basin.
Cloudy conditions with flurries or snow showers continue over much
of the Southwest mainland and Bering Sea/Aleutians.

&&

.MODEL DISCUSSION...

Synoptically, models differ most on the handling of the gale low center
heading north into the Gulf Saturday/Sunday. The NAM seems to the the northern
and eastern most outlier of the model solutions. That said, will be leaning closer to
the GFS/EC models. This will still require hand edits to grids to get desired
Pop/QPF/snow amounts.

&&

.AVIATION...
PANC...
Gusty southerly winds continue across the airport complex into Saturday
morning before diminishing. VFR conditions will likely prevail, but passing snow
showers may briefly lower ceiling/visibilities to MVFR/IFR through tonight.

&&

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

A cold upper low will exert more influence on the region as it
moves north along the Western Alaska Range. Snow showers are
already forming in a convectively unstable environment along the
Kenai Peninsula and these will lift north and form farther east
along the Gulf Coast. Some coastal areas will see some heavy
bursts of snow tonight, especially favored locations like Thompson
Pass. Upper ridging will begin to build Saturday as a warm
front/low moves into the Gulf of Alaska. This low will bring more
moisture and an increase in easterly flow to the coast with
heavier snow moving into the Western PWS/E Kenai including
Turnagain Pass. Strong down-inlet flow will also develop along
the Southern Kenai Peninsula and will likely result in a brief
period of blowing snow Sat evening/Sat night before the front
moves north. Inland areas will also see a threat for snow, but the
front will quickly move overhead which will likely introduce
southeast winds favoring a quick cutoff to precipitation. That
said, there will be a chance for a quick 1-2" snow from Anchorage
to the Southern Susitna Valley Saturday evening/night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3/Tonight
through Monday)...
The cold weather pattern will continue through the next few days
and beyond. An upper-level low lifting northward across Southwest
Alaska tonight will produce snow showers, mainly over interior
Bristol Bay from about King Salmon north and east. Otherwise,
expect continued mostly cloudy skies with isolated showers.

A storm tracking into the Gulf on Saturday now appears likely to
initially take a much farther east track than previous forecasts
indicated. Thus, it now looks like Southwest Alaska will not see
any impacts from this system until late Saturday night or Sunday
morning. At that point in time the low will track into Cook Inlet,
with moisture spreading westward across the Aleutian and Alaska
Ranges. A deformation band will set up in the corridor from
Iliamna to Sleetmute, with at least a few inches of snow likely
along or near this axis. Further west along the Southwest coast,
another round of cold air will lead to gusty winds and snow
showers.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3/Tonight
through Monday)...
Expect very little change in weather over the Bering Sea and
Aleutians as a blocking ridge remains anchored over the western
Bering and a trough over the eastern Bering. A series of upper-level
short-waves will focus shower activity and also help drive
another round of Arctic air southward Saturday night through
Monday. If anything, expect an increase in shower activity as we
head through the weekend. With such cold air aloft, precipitation
will be primarily in the form of snow, though there could be a mix
of rain and snow at times along the Aleutian chain.

&&

.MARINE (Days 3 through 5)...
A series of weak lows will move through the region early next
week. Models are in good agreement that these lows will stay below
gale force, however there is a chance for a few isolated areas
that could briefly reach gale force winds in the Gulf.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long term forecast, beginning Monday night, looks to have a
broad, complex low over the southern mainland. This setup will
keep the region unstable with showers over the area. There is some
inconsistency among the models on when the pattern will shift,
but the general idea is that the low will push off to the
southeast sometime Wednesday with high pressure moving in. The
result for the most locations on the southern mainland will be
that showers clear out. By the end of the week, there is high
model disagreement. Ensembles are preferred at this time.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE... GALE 119
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BC
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SB
MARINE/LONG TERM...MM