Area Forecast Discussion
Issued by NWS Anchorage, AK

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

000
FXAK68 PAFC 241307
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
507 AM AKDT Sun Mar 24 2019

.ANALYSIS AND UPPER LEVELS...
An upper level jet over the Bering continues to drive an occluded
front into the eastern Bering. A second front associated with a
North Pacific low is approaching the western Aleutians this
morning. And the ASCAT/advanced scatterometer which is a satellite
instrument has already detected storm force winds with this low.
A few showers have been detected by the Bethel radar (PABC) as the
remnants of a frontal boundary move across Southwest AK, however
significant accumulations were not observed. Temperatures across
the area have stayed warm. Yesterdays highs include 53F at
Wasilla, 50F at Palmer, 49F at Gulkana and 48F at Anchorage. Rain
and above normal temperatures continue across the North Gulf Coast
from a surface low that moved inland yesterday evening. A front
associated with a North Pacific low will be the key precipitation
and wind driver as it lifts across the Southcentral coast today.

&&

.MODEL DISCUSSION...
For initialization purposes, the 6:26Z ASCAT pass was compared to
the placement of the progged surface lows at 6Z for the NAM, GFS
and ECMWF. The models did really well with the surface low south
of the Gulf of Alaska and capturing the wind shifts associated
with the front moving through the eastern Bering. The synoptic
features of the NAM, GFS and ECMWF are in sync through 6Z Tuesday
and then some divergence becomes apparent with the new low near
northern Japan, the surface low near NE Russia, and the centers
of anticyclonic circulation in the North Pacific at the surface.
The GFS ensemble members are reasonably well clustered early in
the forecast period, but not as harmonious as some of the previous
runs in the past week.

&&

.AVIATION...
PANC...Generally expecting VFR conditions this TAF package.
Overnight, the cigs at PAMR and PANC ranged from 5,000 to 11,000
feet. Gusty winds were recorded at PANC for multiple
observations. The expectation is that the winds will lay down
around 12Z this morning and then pick up again this afternoon.
However, there are some confidence issues with the early portion
of this TAF package, and it is possible that the gusty winds may
linger after 13Z.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A front in the northern Gulf will slowly push inland today. Most
of the precipitation with this front will fall along the coast and
coastal mountains. Fairly breezy winds are expected over the
northern Gulf coast and through Turnagain Arm. As the front pushes
inland later today, southerly winds will increase across
Anchorage as well as the the Knik and Copper River valleys. This
front will push off to the northeast tonight, and upper level high
pressure will begin to build into the area. Conditions will become
dry on Monday across Southcentral as the ridge continues to build
strongly into the the Gulf and southern Alaska. Some patchy fog
is possible near Cook Inlet late Monday night with light winds
and clearing skies. Near the coast, offshore winds will develop.
These are not expected to be very strong as the air mass is fairly
and thus the winds will not be re-enforced by cold air.

&&

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

A fairly active pattern will continue through Monday as a series
of fronts push east from the Bering across the SW mainland. The
first front is already pushing across the Kuskokwim Delta coast
with a band of precip showing up on the Bethel radar over Nunivak
Island and Toksook Bay and SE winds ramp up above 30 mph. Precip
along the coast should remain mostly snow with temps at or just
above the freezing mark with colder air moving in aloft. The front
moves further inland through the day as it loses support and
dissipates bringing only light showers east of the Bethel area.

There will only be a quick break in the weather Sunday night
before a warm front well out ahead of a strong Bering Sea low
pushes north across the SW mainland. The warm front will be
accompanied with strong SE winds and a surge of warm air. Strong
cross barrier flow will lead to downsloping on the west side of
the Alaska and Aleutian ranges leading to unseasonably warm
temperatures for locations like King Salmon and Iliamna, where
high temps on Monday will likely break the 50 degree mark. A
strong cold front is expected to push across the coast by Monday
afternoon. Precipitation should remain mostly rain with warm
surface temps remaining until frontal passage, where snow may mix
in Monday night, but accumulations are not expected. The front
looks to rapidly weaken and fall apart as it moves inland, running
into an upper ridge upstream. By Tuesday, conditions should dry
out through the day as high pressure builds in at the surface.
Temperatures will return to normal as colder air filters in aloft
behind the front.

&&

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

A weakening surface low north of the Bering will continue to
produce southwesterly gale force winds across a large swath of the
western Bering through this morning before diminishing briefly
this afternoon. Attention turns to a rapidly strengthening surface
low approaching the western/central Aleutians from the North
Pacific. Satellite imagery shows the system rapidly developing a
couple hundred miles south of Attu moving northeast. The low is
ingesting cold air off of Siberia while being supported by a
strong 150 kt upper jet, forming in the favorable left-exit region
of the jet. The low is expected to cross the Aleutian Chain
between Attu and Adak Sunday night and enter the western Bering,
deepening to nearly 950 mb. Strong gale to storm force southerly
winds will spread across most of the Bering tomorrow night while a
core of even stronger southwesterly winds is expected to push
across the central Aleutians, especially near Adak, tomorrow
night. Cold air wrapping around the base of the low is expected to
enhance winds in this area, with gusts expected to be hurricane
force, thus a High Wind Watch was issued for Adak for tomorrow
night. The low will track north out of the Bering by Monday
afternoon, though gale force winds will remain across most of the
western Bering through Tuesday. Cold air under an upper low will
dominate the Bering leading to blustery and showery conditions.

&&

.MARINE (Days 3 through 5)...

Gulf of Alaska... Expect generally benign conditions, with winds
diminishing and seas subsiding as pressure builds.

Bering Sea... Winds will diminish and seas will subside Tuesday as
the former storm force low continues to fill and shift northward.
Then, expect generally benign conditions, with one small caveat. A
low currently roughly 800 miles off the coast of Japan will track
northeastward through Thursday. Its expected trajectory is highly
uncertain, and it`s possible that it will track far enough east to
bring gales to the western Aleutians and Bering Sea Thursday.

&&

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

Confidence remains high that the long term period will begin with
an upper high over Southcentral that will slowly drift eastward,
and with a low upstream moving from the northern Pacific eastern
Siberia. Thus, expect dry weather, warm afternoons, and
relatively cold nights driven by limited cloud cover over
Southcentral and the southwest mainland. That said, with ample
surface moisture and atmospheric stability, there will also be
potential for morning fog, especially in Southcentral which could
decrease the diurnal temperature range. Farther west, a shortwave
trough will bring a brief round of precipitation and south winds
from west to east Wednesday, likely fizzling before reaching the
AKPEN.

Forecast uncertainty increases substantially Thursday. The
aforementioned low will either shift towards the Sea of Okhotsk,
or take a more eastward track towards the Kamchatka Peninsula.
The latter track would yield a wetter, windier pattern for the
Aleutians...and which progression actually occurs will depend on
what happens upstream, i.e., how far east the high over
Southcentral shifts. Unfortunately, models have little consistency
between runs, between models, and between ensemble members. So for
this forecast package, continued a blend with pops slowly
increasing from western Aleutians towards the AKPEN through
Saturday. Be sure to monitor the forecast as it will probably
change over the coming days.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Watch 187.
MARINE...Gales 155 165 170 172 173 174 180 181 411 414.
 Storms 175 176 177 178 179 185 412 413.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...PAMBER
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KVP
MARINE/LONG TERM...MM


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.