Gale Warning 206, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
402 PM AKDT Mon Mar 11 2019

.ANALYSIS AND UPPER LEVELS...
A broad upper trough extends from over western Alaska to the
northern Gulf. Widespread rain and snow showers were evident
across the North Gulf, and the Kenai Peninsula north to the
Susitna Valley. Cooling temperatures aloft kept most of the
showers over Southwest Alaska as snow with generally mixed rain
and snow showers across the Eastern Bering Sea and Alaska
Peninsula. A surface low was present near Adak with its occluded
front extending east to Unalaska. Rain was evident near the low
center and along the front over the central and eastern ALeutians.
Colder air wrapping around the backside of the low brought snow
showers and gusty north winds to the western Aleutians.

&&

.MODEL DISCUSSION...
Models are in good agreement through Thursday afternoon. However,
with such a broad cyclonic pattern, they will generally struggle
with meso-scale features (showers, local winds, etc.). Confidence
is moderate to high with the next storm force low moving north
across the Gulf Tuesday night and Wednesday.

&&

.AVIATION...
PANC...Generally should see VFR conditions though ceilings may be
in the lower end below 5000 ft tonight. Gusty south winds should
diminish late tonight.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A cool upper trough continues to shift east this evening with
cold air advection seeping through the Alaska Range and moving up
Cook Inlet. A more moist southerly onshore flow continues along
the coast and into Prince William Sound, with those showers also
forming along the Kenai Mountains/Turnagain Arm and moving north.
Quite a bit of warm air in the low levels will keep precipitation
mainly in the form of liquid until later this evening as it turns
to all snow. However, little to no accumulation is expected
except along the Hillside and into the Mat Valley/Northern
Susitna. Light accumulations will also fall over the mountains.

Tuesday will be mostly dry as the next low moves into the Gulf of
Alaska, and upper ridging builds aloft ahead of it. Onshore flow
along the coast, and a return of cold air behind this first
trough, will favor mostly snow (mixed with some rain at times)
along the coast before the front moves along the coast Wednesday
as a storm force front. As a wrapped up occluded low,
precipitation will heavily favor western Prince William Sound
given the strong eastward component of low level flow. This will
also favor strong downslope flow, so interior locations will trend
warmer with some breaks in sun at times by Wednesday afternoon.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2/Tonight
through Wednesday night)...
A weak low over interior western Alaska will retreat northward
tonight, with snow shower activity over Southwest Alaska
gradually diminishing. There won't be much of a break between
storm systems though, as a low along the Aleutians tracks to the
eastern Bering Sea late tonight. A leading occluded front will
clip portions of Bristol Bay (mainly from Dillingham north and
west) late tonight into Tuesday morning, then continue northward
to the southern Kuskokwim Valley and the Kuskokwim Delta. Expect a
quick burst of snow as this front moves through. Gusty southeast
flow will then move in behind the front causing temperatures to
rise through the 30s. The low and front will ultimately settle in
just off the Kuskokwim Delta coast, so expect periods of light
snow through Wednesday along the coast. A deep low will track into
the Gulf of Alaska on Wednesday which will cause the gusty
southeast winds to die down over Southwest. Most of the
precipitation will remain over the Gulf, with perhaps just a few
showers making it over the mountains into Southwest Alaska.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The low pressure system along the central Aleutians this afternoon
will track quickly to the eastern Bering Sea late tonight.
Precipitation spreading out ahead of the low may start as snow,
but expect a quick turn-over to rain along the southern Alaska
Peninsula and eastern Aleutians this afternoon through evening.
The upper level trough overhead of this low will amplify over the
northwest Pacific as a jet streak dives down the back side of the
trough. As a result, arctic air will spill southward behind the
surface low, changing precipitation back to snow along the
Aleutian chain. Gusty winds and snow showers will settle in
across the entire region on Tuesday and persist through Wednesday
night.

&&

.MARINE (Days 3 through 5)...
We are still expecting storm force winds with a low pressure
system in the Gulf of Alaska into Thursday morning. Models differ
slightly in the placement of the low, but due to the setup of the
system we have high confidence storm force winds will be present.
Another low enters the Gulf on Saturday and we have low confidence
in its track at this time due to poor model agreement. However,
its looks like small craft to gale force winds will be present.
Meanwhile in the Bering, it will be quiet with moderate northerly
flow. This does mean the ice pack could grow in zone 185 and along
the coast near Nunivak Island.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Models are agreeable to start the longterm, but quickly fall
apart going into the weekend. General low pressure will be present
over the eastern Bering Sea. Two rounds of low pressure will be
impacting the Gulf of Alaska, with one of them already present to
start the long term Thursday morning. The next will move in from
the south on Saturday. However, there is considerable
disagreement in the placement and timing with the second low
pressure system. What this means for the extended forecast is a
broad brush approach using an ensemble of models to get very
general timing and and placement of weather. This also means low
forecast confidence in the long term. So, we will remain in an
active weather pattern for the next week or so, but we will have
to work on the details over the coming days.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 139 155 165 172>176.
 Heavy Freezing Spray 181 185.
FIRE WEATHER...NONE.

&&

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