Gale Warning 748, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
500 AM AKST Sat Dec 21 2019

.ANALYSIS AND UPPER LEVELS...
Arctic air continues to drain southward. However, the bulk of the
coldest air remains locked north of the Alaska Range. Where the
skies were clear over night, radiational cooling occurred and a
number of locations in southcentral dipped into single digits and
below zero. On satellite imagery, there is a decaying frontal
boundary in western Alaska and a mature low in the North Pacific
with the leading edge of the cloud shield approaching Unalaska.
ASCAT/advanced scatterometer has detected gale and storm force
winds in the north Pacific associated with this low pressure
system. The jet core that is driving the Pacific storm was pegged
at 160 knots.

&&

.MODEL DISCUSSION...
Models remain in good synoptic agreement through Monday morning
from the Gulf Of Alaska to the North Pacific. Monday problems
emerge with a low near Bristol Bay. This low is headed eastward
but there is no consensus with the precise track yet. Overall,
next week looks more active with the potential snow for the
Anchorage Bowl.

&&

.AVIATION...

PANC...VFR conditions and light winds are anticipated this TAF
package.

&&

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

A weakening frontal system moving east across the mainland will
bring some clouds, but generally dry conditions with offshore flow
in the lower levels will prevail through today. Some light snow
with an upper wave and surface low over the eastern Gulf will
bring a little snow to the eastern Copper River Basin tonight.
Strong outflow gap winds across coastal locations in the northern
Gulf and NW gales across the Barren Islands will slowly diminish
through this evening. A triple point low develops along an
eastward moving front near Kodiak Island Sunday morning. This low
then heads slowly northeast and intensifies as the front moves to
the North Gulf Coast Sunday evening. These systems will initially
bring snow to Kodiak early Sunday morning which should then
transition to rain fairly quickly. Overrunning snow heads north
into Southcentral during the afternoon and evening hours on
Sunday. The brunt of precipitation(mainly snow) through Sunday
will likely be over the southern and eastern Kenai Peninsula and
Gulf Coastal locations. The deep cold airmass to the lee of the
Chugach/Kenai mountains will allow light snow to move inland as
moist southeast flow rides over the cold air.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

Southwest Alaska starts out with cold and dry weather in place.
Lows in interior areas of southwest AK will drop to the minus
teens tonight, with light flow from the Interior in place. This
will begin to change Sunday with the approach of a powerful low
pressure system in the Bering. This low will send a frontal system
into the southwest coast Sunday, bringing snow and increased wind
speeds, mainly for areas near Bristol Bay. This will cause blowing
snow with some visibility reduction possible. Interior areas of
southwest Alaska will still remain cold, with some increase in
cloud cover and light snow. Additionally, we are still looking
into elevated water levels along the coast, however the potential
looks low as of now for any surge.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

The powerful low anticipated for the Bering and Aleutians has made
its arrival, with the low center just now approaching the western
Aleutians from the southwest. It is well defined on satellite as a
mature, well wrapped low. As this low progresses east, it will
bring strong winds will cold air advection behind it. This is
where the main weather threat will be, with Hurricane Force winds
forecasted. The main core of these winds will remain over the
central Bering and are not expected to impact the Aleutian Islands
themselves. However, winds do look strong enough to keep the High
Wind Warning in effect for the Central Aleutians. We decided to
cancel the high wind watch for the Eastern Aleutians though, as
it looks like the low will be weakening by the time it reaches
there and the strongest winds will stay north of the islands.
Models were speeding the low up a bit and satellite does show it
moving pretty quick, so progressed it a touch quicker in the
forecast tonight. Otherwise, the forecast is on track with this
system.

&&

.MARINE (Days 3 through 5)...

Beginning the extended period marine forecast on Monday afternoon,
a weakening and departing gale force low in Bristol Bay will fall
apart by Tuesday morning. The Pacific storm track will shift
south of the Aleutian Chain through Thursday and move into the
Gulf of Alaska as a series of lows moves into the Gulf. Currently
the first will move into the Gulf by Tue and last through
Wednesday, possibly as a gale force low as it tracks north to the
Gulf Coast. A second low, possibly stronger, moves in sometimes
Wednesday/Wednesday night. Over the Bering, this pattern will
keep a cold, northerly or northeast flow over that area with areas
of freezing spray.

&&

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

The long term will kick off Tuesday with a deep pool of cold air
over the majority of mainland Alaska. A Bering low looks to track
across the northern Gulf Tuesday along the boundary of cold arctic
air spilling out of the state. Model guidance suggests a winter
precipitation event along the southern coast as the low moves
east. Another low in the Western Aleutians Tuesday is expected to
track across the Aleutian chain and into the northern Gulf on
Wednesday through Thursday, adding reinforcements with another
round of winter precipitation. Guidance is mixed on the exact
track of these two storms, but model guidance suggests that we
will be covered in cold air and odds for some wintry weather are
strong.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 185.
MARINE...Heavy Freezing Spray 129 140 180 181. Hurricane Force 413
173 175 177. Storm 411 412 165 170 171 172 174 176 178. Gale 120
121 130 131 132 185 138 139 351 352 414 150 155 160 179 180 181.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...RC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BJB
MARINE/LONG TERM...JA/LB