Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 150156
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
456 PM AKST Wed Feb 14 2018

.ANALYSIS AND UPPER LEVELS...
The 500 mb ridge has moved eastward to near the Alcan border with
a trough over Southwest Alaska providing enough lifting in
southwest flow for widespread light precipitation. This trough
continues to progress eastward and will move over Southcentral to
the Copper River Basin overnight. The next upper level ridge is
amplifying in the eastern Bering Sea today and will move over
Southcentral by tomorrow afternoon. A deep upper level low remains
anchored near the Kamchatka Peninsula, allowing the ridge to
amplify over the Bering Sea to its east. The surface gradient
along the north Gulf coast has diminished, bringing outflow winds
to an end. However, winds will increase again tomorrow with the
building ridge.

&&

.MODEL DISCUSSION...
For the second day in a row the 12Z and 18Z model runs have
brought a much better semblance of consensus on the low tracks
and the expected central pressures. This is the case for both the
Gulf of Alaska and Bering Sea regions into the weekend. Models all
remain consistent with the surface ridge moving over the mainland
part of the state early in the weekend and edging eastward to the
Alcan border by the end of the weekend.

&&

.AVIATION...
PANC...Periods of snow will affect the airport this afternoon and
evening, lowering to MVFR conditions and perhaps briefly down to
IFR. Ceilings and vis should improve quite a bit in between bands
of snow. Mid and upper levels will rapidly dry out behind the
upper trough axis after midnight, so it looks favorable for
stratus and fog to develop, with IFR or even low IFR conditions
possible between 12z and 18z. Forecast is conservative
(optimistic) for now, but will re-evaluate fog potential as this
system evolves this evening.


&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A shortwave is pushing through Southcentral Alaska from the west
which is bringing snow to the area that will track east through
Thursday morning. The wave looks to move through relatively
quickly which will help keep total snow amounts low. Behind the
shortwave, high pressure will build in from the west which will
clear out the snow and cloud cover Thursday. Thursday night into
Friday another system will approach the area from the southwest
bringing rain and snow to Kodiak Island. However, with the low
tracking east through the southern Gulf, little precip will make
it further north to the rest of Southcentral Alaska.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
(Tonight through Friday)
The weak surface front which brought light snow to much of
Southwest Alaska is about to exit the region, as it`s currently
aligned with the Alaska Range. Much drier air with clearing skies
will overspread the region overnight, allowing temperatures to
plummet, with most locations being about 10 to 15 degrees cooler
than last night. The departing front will also allow for a
decreased pressure gradient. With partly cloudy skies and low
level moisture remaining from the recent snowfall this will
provide a good radiational cooling setup. Thus, look for areas
of fog to develop this evening into the overnight hours while
expanding in coverage.

Our attention then turns to another approaching front for Thursday,
with the latest model guidance showing a coastal arrival in the
mid afternoon time frame, continuing eastward while weakening
some for Friday. Widespread precipitation will once again
accompany this front, most of which will be in the form of snow.
However, frontal speed will temporally limit any snowfall
accumulation potential, with just light amounts expected.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
(Tonight through Friday)
Clearing skies have overspread much of the eastern Bering through
the AKpen, with light winds in place as well. Was tempted to add
patchy fog to the forecast for the Peninsula. However, winds
should become southeasterly overnight while increasing in speed
some compared to the Mainland, with mixing helping mitigate this
potential. Otherwise, look for a storm force low to continue
moving northward through the western Bering, sending a front
eastward through he chain. Strong gusty winds and increasing
precipitation coverage/intensity will precede this front as it
continues its eastward trek, with more showery precipitation
behind it and winds dropping off to gales the further away from
the low one travels.

&&

.LONG TERM FORECAST (Days 3 through 7)...
As a decaying front across the Anchorage area slides East on
Friday afternoon, only a slight decrease to temperatures and
increase of clouds are to be expected. Temperatures aloft will
cool through that time but begin to rebound into the weekend and
beyond. Skies are expected to clear out by the early weekend. Now
that we are back into the season of the sun helping to aid in
warmth, daytime temperatures will quickly rise. Diurnal swings of
20 degrees, or more, are not out of the question. Interior and
river valley areas of the Copper River Basin should see night
temperatures drop well below zero as any warmth radiates out
overnight. Clouds will increase Sunday afternoon with an
approaching front from the west. However, guidance has a harder
time figuring out how far the front will move to the east. If it
has enough oomph to overtake the ridging over the area, we may see
snow Monday afternoon into the evening hours. The GFS is showing
the strongest of these signals. The EC is indicating a much weaker
front with light snow, and the Canadian is showing nothing.
Regardless, the nature of ridging and troughing will continue
progressively through this weekend and into next.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Heavy Freezing Spray Warning 181.
         Storm Warning 177.
         Gale Warning 173 174 175 176 178 179 180 181 185.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...SS



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