Gale Warning 144, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
410 AM AKST Sat Feb 9 2019

.ANALYSIS AND UPPER LEVELS...
The synoptic set up persists with a highly amplified ridge across
the North Pacific to the Central Interior and a mature low
pressure system to the west, centered over Kamchatka and filling
on a northward track. Low clouds and patchy fog are noted across
the southern mainland with precipitation moving into the Kuskokwim
Delta as the next front moves to the coast. Winds have tapered
down across the Bering as the storm begins to weaken.

&&

.MODEL DISCUSSION...
Models are struggling with how to handle the pattern transition
tonight as the upper low over the Bering moves a strong shortwave
east. NAM was the outlier on the 00Z model run; therefore, changes
were made using the GFS which was a middle ground solution between
the inherited blends and ECMWF. Precipitation was hedged down
across Southcentral locations as models are trending further south
on a surface low that tracks south of the Alaska Peninsula to the
Gulf tonight into Sunday. Stronger winds are still expected around
this low, but the focus is further south. The main challenge
across the southwestern areas of the state continues to surround
gusty winds and precipitation type.

&&

.AVIATION...
PANC...VFR conditions are expected lower to MVFR later this
morning as the predominant mainland and Gulf ridge shifts its
influence back over the area this afternoon and evening. MVFR
conditions should be prevailing through Sunday morning; however,
there is a shift in stability with a low moving across the
southern gulf late tonight which may improve ceilings at times.
Winds should remain light under weak surface pressure.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Upper level high pressure will remain over the area through
tonight. On Sunday the ridge will slide east as a strong trough
moves in from the west. Most of the energy with this trough will
Push into the Gulf, with a closed low developing just south of
Kodiak Island Sunday morning. A decently strong surface low will
be vertically stacked under the upper low. High pressure will
rapidly build behind this low with Storm force winds over the
southern Marine zones. Further north, precipitation with this
system will reach the Kenai Peninsula early in the morning, and
push eastward across the north Gulf coast during the day. For
inland areas precipitation chances are not looking as promising as
they were on previous model runs, as the low is forecast to track
further south. Thus the Pops have been lowered a bit. On Monday
night the northern portion of the trough will cross the
Southcentral mainland, but should be quite weak and not produce
much precipitation.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
A warm front lifting north this morning is bringing areas of rain
to the lower Kuskokwim Valley. Ahead of the front, where
temperatures are hovering at or just below freezing, precipitation
is falling as snow or a mix of snow and freezing rain. The frozen
precipitation will quick transition to rain, however, as a warm,
southerly flow sets up behind the passing front. Tonight, a front
will move in from the west, changing rain back to snow from west
to east. Light accumulations are possible through early Sunday
with higher amounts along the windward side of the Kilbuck and
Alaska Range. A ridge will build in behind the front for the
second half of Sunday. Areas of fog are possible Sunday night into
early Monday morning, especially from Bristol Bay north and east
into the interior valleys as the ridge crests overhead and the
flow at the surface slackens.

Active weather then returns early Monday as an occluded front
attached to a strong surface low in the western Bering advances on
the region. Cold air at the surface will allow the precipitation
to begin as snow everywhere with the exception of the southern
half of the AKPEN. Increasing gusty, southeasterly winds along the
coast will produce areas of blowing snow on Monday, especially
over the YK-Delta. Precipitation is then expected to transition
to a brief period of a wintry mix of snow and freezing rain from
around King Salmon north to Bethel before changing to all rain as
warmer air moves in. The precipitation is expected to remain all
snow in the far interior southwest. The front moves inland late
Monday with colder air again advecting across the southwest from
west to east. This will change rain along the coast then back to
snow.

The prolonged southerly wind Sunday into Monday is expected to
cause water levels to rise along the coast from Kuskokwim Bay to
Hooper Bay. Currently, these levels are expected to reach near
HAT, give or take. Depending on the timing of this event in
conjunction with high tide, this may lead to some coastal erosion
along ice free shores. Stay tuned for updates.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
A storm force low tracking north along the coast of eastern
Russia continues to produce strong westerly winds and snow showers
across much of the Bering. A front associated with this low arcs
from the northern Bering south across the Pribilofs and central
Aleutians. This frontal system will continue to push east today
with a new surface low developing along it. This will help enhance
the southerly flow, pushing more moisture north over the eastern
Bering. Another rapidly deepening surface low will then approach
the western Aleutians on Sunday. This system will swing a warm
front across the western half of the chain, bringing with it
widespread precipitation and strong gales. As the front tracks
north and the trailing cold front pushes east, colder air wrapping
around the back side of strengthening low will produce a large
area of storm force winds, and possible a smaller core of
hurricane force winds, across the western Aleutians and Bering
Sunday night into Monday. Storm force winds are possible for the
Pribilofs late Monday as this system continues to lift north.

&&

.MARINE (Days 3 through 5)...
The active storm track in the Western Bering will continue Monday
through Wednesday as low after low moves northward along the
Russian coast. On Monday, a strong storm will cross the Bering Sea
and head towards the Bering Strait. This storm will bring strong
gale force winds from the east ahead of it, while behind the
front, southerly to southwesterly gale to storm force winds will
follow. This will be a broad area of storm force winds, and it is
expected to make its way into the Central Bering on Tuesday.
Westerly winds are expected to remain near gale force through the
Bering through Wednesday, when the next storm approaches from the
west. At this time, there is some difference between on the timing
and location of the next low, but it appears to be consistently
strong, so the potential for storm force winds ahead of the front
exists for the western Bering again on Wednesday.

Meanwhile, conditions in the Gulf of Alaska appear to be somewhat calmer
than the Bering for the 3 to 5 day period. High pressure building
in beforehand will weaken the trough that crosses the Gulf on
Monday. Behind this front, northwesterly winds will increase
through the Gulf, reaching gale force through the channeled areas
and the Barren Islands, but diminishing rapidly further away from
shore. There is some uncertainty whether these northwesterly winds
will weaken during the 5 day period, or whether they will
maintain gale force through Wednesday as a low develops in the
eastern Gulf.

&&

.LONG TERM FORECAST (Days 3 through 7)...
There is surprisingly good agreement between models at the
beginning of the long term forecast for what will be an active
storm period over the next week. A strong low pressure system
somewhere around 960mb will move northward along the western
Bering, bringing strong southerly to southwesterly flow for most
of the West Coast. With this low pressure system comes a large
slug of warm air, meaning that Monday will be warm, wet and windy
along the West Coast, which will then quickly be followed by more
seasonable cold temperatures on Tuesday. Conditions east of the
Alaska Range are a little more uncertain due to the fact that the
models are having difficulty resolving the strength and location
of the low that develops in the Gulf of Alaska. At this time, it
looks like a quick shot of precipitation (snow mixing with rain
further south) in the Monday time frame, then rapidly cooling with
gusty outflow winds beginning Tuesday.

Later in the week, the forecast becomes slightly more uncertain,
due to model differences on a developing low in the Western
Aleutians beginning Wednesday. However, a developing ridge ahead
of this front promises colder temperatures across the mainland
through Friday, with the possibility of outflow winds along the
coast in the usual windy areas. As for the Bering Sea, timing may
be uncertain, but stormy conditions are expected through the end
of the week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning 132 138 150 155.
 Gale Warning 160 165 172 174>181 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KH
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
MARINE/LONG TERM...LF