Gale Warning 32, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
523 AM AKST Tue Jan 1 2019

.ANALYSIS AND UPPER LEVELS...
The latest round of the series of lows impacting our forecast
area rings in 2019. This New Year's low is another powerful one,
producing hurricane force wind gusts in multiple locations. This
low is the last of a series of lows that have been attached to an
area of broad upper level low pressure over the Bering Sea. The
firmly entrenched trough set the table for these lows to develop
into powerful systems. Our forecast area has also been sandwiched
between this area of low pressure and an upper level ridge to our
east, creating this active pattern.

Today we can expect a shift in the pattern which will end this
train of strong lows. The ridge of high pressure pushes off over
the Canadian Rockies while the area of low pressure lifts north,
transitioning us to a more zonal pattern. This will allow some
smaller lows to move quickly west to east across our forecast area
that will be embedded in this fast paced flow. However, they will
not be able to develop into the deep, powerful lows we have been
seeing with the absence of the longwave trough.

&&

.MODEL DISCUSSION...
Models are performing better today. They have good agreement with
the track of the low currently pushing through our area. All take
the track almost straight north through western Alaska. Models
were generally correct with the strength of winds this latest
system. However, models overestimated the strength of the system
in terms of precipitation in southwest Alaska. Continuing the
trend as of late, the quality of model guidance falls apart after
about 48 hours. So, that coupled with the active weather means we
concentrated on the first 48 hours in today's forecast.

&&

.AVIATION...
PANC...VFR conditions will persist for the TAF period. Winds will
continue to be an issue. Light winds early this morning will be
the cause of low level wind shear as winds aloft are still strong
out of the southeast. Winds will once again descend to the surface
later this morning to produce gusty winds out of the southeast for
the remainder of the TAF period.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2/Today
through Thursday night)...
A strong front will push on shore of Southcentral early this
morning. Gusty southerly winds will then spread inland, with the
strongest winds early to mid morning. Winds will then diminish a
bit most places, but remain gusty all the way into Wednesday. The
Kodiak Island waters on up to Cook Inlet will see another round of
storm force southerlies today thanks to cold air wrapping around
the south side of the low tracking northward across Southwest
Alaska. Pressure rises will also contribute to the strength of the
winds.

With a mean southerly flow through the lower atmosphere,
precipitation will be favored along south facing mountain slopes.
However, with increasing instability there could be a few showers
just about anywhere. The winds will help mix warm air down to the
surface (just like on Monday), with temperatures climbing to the
upper 30s to lower 40s for much of Southcentral. Thus, the
predominant precipitation-type near sea level will be rain.

As the low exits to Interior Alaska tonight, flow will shift to
southwesterly and colder air will slowly make its way across
Southcentral. The continued gusty winds will help keep surface
temperatures elevated near or above freezing. Thus, expect a slow
transition to snow, with many areas remaining rain or a rain/snow
mix for tonight. Winds will finally begin to die down Wednesday
through Wednesday night while even colder air will advect into the
region from the west. Thus, precipitation will eventually turn to
all snow. A series of upper level short-waves will continue to
traverse Southcentral through Wednesday night. Based on the the
track of these and the southwest low level flow, this will favor
snow accumulation for Anchorage and the Mat-Su as well as the
Valdez/Cordova areas in eastern Prince William Sound.

&&

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

Ending the train of storms that have been impacting Southwest
Alaska for the better part of a week now, a final strong area of
low pressure is currently tracking into the Bristol Bay area
between King Salmon and Dillingham. The low is moving northward,
but at a fairly slow pace, so Southwest Alaska will be impacted by
the low through tonight. Thus far, the storm has fallen short of
expectations for the most part, with few areas seeing snow drop
visibilities even to 1 mile. The strongest winds stayed up in the
Aleutian range, where the Coville site gusted to 76 mph around 1
am this morning. As the low lifts northward into Interior Alaska
and weakens tonight, the flow will flip out of the west to
northwest as colder air moves into Southwest Alaska. On this wind
direction, upslope snow will develop on the west sides of the
Kuskokwim and Aleutian ranges, including areas from Bethel east,
Sparrevohn, Iliamna, and on down to King Salmon. The snow is not
expected to be heavy, but will likely leave some minor
accumulations. Elsewhere, the primary weather story will be the
return to much more seasonable, wintry temperatures. Today's highs
will likely occur in the morning, with a slow descent beginning
thereafter depending on how quickly the storm moves out of the
local area and how quickly the clouds dissipate. The coldest air
is really more likely to move in tonight so that by Wednesday,
high temperatures are at least 10 degrees below today's forecast
highs, and across the Kuskokwim Delta, closer to 20 degrees
colder. Other than some lingering mountain snow showers on
Wednesday morning, parts of Southwest Alaska should see a decent
amount of sunshine as the area gets a break in between systems.
The next front moves into the coast late Wednesday night into
Thursday, but it should be emphasized that unlike the past number
of storms, this one is expected to be weak and the impacts
minimal.

&&

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

Despite there being a strong low moving into Southwest Alaska,
this represents the quietest the Bering Sea basin has been in
quite some time regarding where potentially hazardous weather may
be occurring. A secondary much weaker low, the remnants of the
giant low that hit the western Aleutians with hurricane force
winds several days ago, is now centered between the Pribilofs and
Unalaska this morning. This low will soon be absorbed into the big
low over Southwest Alaska, becoming a cold front as a result.
However, as it does so, it will phase with some upper level
energy, which will enhance the pressure gradient behind the low as
it passes Unalaska. This will cause gale force winds with gusts
above storm force to impact many of the Eastern Aleutian islands
this morning. Snow showers may also impact those areas at the same
time, which may cause brief periods with near whiteout conditions
across the area today. That said, the combination of the small
size of the low and that it will be rapidly weakening should keep
any hazardous conditions to only brief periods. Once the low
dissipates later today, essentially the entire Bering will be
under a polar air mass. Frequent spinups of small, weak meso-
lows that may briefly bring winds up to small crafts, but tracking
those small, weak lows is very difficult. A more consolidated low
tries to develop across the northwestern Bering late Wednesday
night. Otherwise most of the area can expect seasonably cold
conditions with frequent ocean-effect snow showers through into
Thursday.

&&

.LONG TERM FORECAST (Days 4 through 7)...

Southcentral:

Beginning the extended period forecast Wednesday night, there
will be a series of low amplitude shortwaves in southwest flow
aloft moving across the region. These will not be strong lows, but
with much colder air aloft (850 hpa temps around -10 to -12C),
there will be the possibility of snow across all parts of
Southcentral, although snow will generally be light. The threat
ends late Thursday with cold high pressure developing for the
weekend. This will result in cooling temperatures and eventually
below average temperatures,in conjunction with clearing skies. By
Monday, threats for coastal precipitation increase, but it looks
like colder high pressure may dominate inland weather heading into
early next week.

Southwest/Bering Sea:

Over the mainland, Arctic air will push southwestward through the
weekend, and conditions will trend colder and drier day after
day. An upper trough will persist over eastern Siberia, and expect
weak shortwaves to continue rotating around the base of the
trough Thursday. This will bring showers over the Bering and
Aleutians, possibly even into Bristol Bay and the Y-K Delta
Thursday. The upper trough will amplify Thursday into Friday and a
cut off low will form, bringing potential for gale force winds
over the western Aleutians Friday into Saturday. The forecast
becomes more uncertain Saturday, with run to run consistency poor.
In general, models point to a stronger low developing north of
the jet stream, bringing another round of strong winds to the
Aleutians Sunday or Monday. That said, much will depend on the
track of the low which models have had a tough time resolving.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Small Craft...121 175 176 177 178 185
         Gale...120 125 128 129 136 137 139 140 141 155 160 165
         170 171 173 174 179 180 351 352 413 414
         Storm...119 130 131 132 138 150 172
         Brisk Wind...181
         Heavy Freezing Spray...185

&&

SYNOPSIS AND MODEL DISCUSSION...BJB
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JPW
LONG TERM...JRA/MM

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
1141 AM AKST Tue Jan 1 2019

AKZ121-032045-
Western Kenai Peninsula-
Including the cities of Kenai, Soldotna, Homer,
and Cooper Landing
1141 AM AKST Tue Jan 1 2019

...MINOR FLOODING POSSIBLE ON THE ANCHOR RIVER NEAR ANCHOR
POINT...

The Anchor River near Anchor Point is above bankfull.

PRIMARY CAUSE: Warm temperatures and precipitation caused a possible
ice jam.

REASON FOR WARNING/ADVISORY:
A small ice jam may cause minor flooding on the Anchor River near
Anchor Point. The situation may improve once temperatures drop
and precipitation ceases.

EXPECTED IMPACTS: Low lying areas such as the campground may be
impacted by conditions about a foot above bankfull.

Ludwig