Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 230059 CCA
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
459 PM AKDT Sun Mar 22 2020

.ANALYSIS AND UPPER LEVELS...

High pressure over the eastern Bering continues to bring calm and
sunny weather across much of the state. In the Panhandle, a
surface low continues to drift off to the southeast. Between the
high in the west and the low in the Panhandle, a tightened
pressure gradient has caused gusty northerly wind through much of
the forecast area. Along the North Gulf Coast, channeling has
increased the wind strength and winds through Valdez were gusting
up to 45 mph this morning. Some blowing snow occurred through
colder areas like Thompson Pass overnight, but with warming
surface temperatures today, conditions have improved. Fog occurred
overnight in the Susitna Valley and along Cook Inlet, but has
since burned off this morning.
Out west, sunny conditions persist over most of the Bering Sea,
with clouds creeping in just south of the Aleutians. A trough
dipping down from the Arctic is bringing some clouds and westerly
winds to the Kuskokwim Delta, but little precipitation.

&&

.MODEL DISCUSSION...

Models are in fairly good agreement in the short term. Starting
Tuesday, there are some differences in the effects of the
northerly trough. NAM seems to be the quickest and brings the most
precipitation in, while the GFS lags slightly behind. Today`s
forecast attempted to strike the middle ground between those
solutions.

&&

.AVIATION...

PANC...Light winds and VFR conditions will persist.

&&

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

Strong northerly outflow winds will continue through the next 24
hours due to the tight pressure gradient between a surface ridge
extending across the interior of the state and an elongated trough
of low pressure over the northern Gulf. These winds will begin to
diminish in intensity tomorrow as the trough dissipates and a
ridge of high pressure extends across the western half of the
Gulf with more of westerly flow aloft developing.

Clear and dry conditions will also persist across the region due
to the ridge and northerly flow. A few mid and high level clouds
will skirt the northern portions of the Susitna Valley and Copper
River Basin tonight through Monday as a series of upper-level
shortwaves track east across the Alaska Range. Although it will
remain dry across much of the area, patchy fog is once again
possible overnight along Cook Inlet and around Talkeetna, as weak
surface winds have yet to scour away all of the lingering low-
level moisture.

A more significant shortwave moves across Southcentral overnight
Tuesday into Wednesday. This system will spread clouds over the
region along with areas of light snow for interior locations and a
mix of rain/snow for the Kenai Peninsula and Gulf coast. There is
still some model uncertainty as to how widespread the
precipitation will be, but given the uniform westerly flow and
lack of deep moisture advection, the bulk of the precipitation
will likely occur along the upslope areas of the mountains. A
second shortwave then drops south from the interior later on
Wednesday with better upper-level support. This will help maintain
the cloud cover across Southcentral and produce additional light
snow for the northern half of the Susitna Valley, Copper River
Basin, and higher elevations.

&&

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

A 1046 mb high over the Bering Sea will keep things quiet for the
next 24 hours for southwest Alaska. An upper level disturbance
will bring precipitation chances back to the Kuskokwim Delta on
Monday night. Temperatures should be cold enough for snow during
this event. A north Pacific low will lift into the Bering by
Tuesday afternoon and things will shift, as the high pressure of
recent days weakens. Warm air advection pushing onshore will
likely deliver some freezing rain chances late Tuesday night
before switching over to rain. An active pattern will keep
precipitation chances in the forecast through Wednesday and beyond
for Southwest Alaska.

&&

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

High pressure will keep much of the Bering and eastern Aleutians
quiet for the next 24 hours. A frontal boundary from a north
Pacific low will lift into the western Aleutians tonight and bring
precipitation and some gusty winds. As this boundary spreads
northeastward the Pribilofs can expect some rain and snow chances
Monday morning. As the parent low lifts across the western
Aleutians precipitation will increase for the eastern Aleutians
and the Pribilofs on Tuesday. As the system weakens into a series
of upper level troughs Tuesday night, precipitation chances in the
Bering will continue for the Pribilofs and eastward through
Wednesday.

&&

.MARINE (Days 3 through 5)...
Winds should not exceed small craft advisory through Thursday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Strong confidence remains that an upper level ridge will remain
over the southern part of Alaska through the middle of the week.
Early Tuesday morning, a North Pacific low will get caught up in
the backside of the ridge, which will bring it northwest across
the western Aleutians and into the Bering Sea. This low will
weaken the ridge, thereby flattening it, and will force the low
southeastward across the eastern Aleutians and right back into the
North Pacific through Thursday. Following this, zonal flow aloft
will be the dominant feature into Friday. Afterwards, an upper
level ridge will build across the Bering Sea until an upper level
trough upstream enters the western Aleutians Friday night. This
will bring precipitation to the western Aleutians/Bering and
across into the eastern Aleutians through Sunday. During this
time, an upper level trough looks to dip down from northern Alaska
and into Southcentral before becoming a closed off low Saturday.
If this solution holds, chances for precipitation will return to
Southcentral through Sunday.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales 130 and 131.
FIRE WEATHER...NONE.

&&

$$

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



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