Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 250125
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
425 PM AKST Sat Feb 24 2018

.ANALYSIS AND UPPER LEVELS...
The upper level short-wave and associated surface low which
brought another round of light snow to most of Southcentral
last night through this morning is exiting eastward across the
Gulf. Cold air advection is leading to strengthening gap winds
along the Gulf coast. Winds are particularly strong across the
western Gulf/Kodiak Island thanks to steep low level lapse rates
(7 to 8 degrees C/km on the 12Z Kodiak sounding), with stronger
winds mixing down from aloft. This unstable airmass extends back
westward into the eastern Bering Sea, Bristol Bay, and along the
Alaska Peninsula, where gusty winds and snow showers prevail.
Weak troughing persists across the rest of Southwest Alaska,
with a few lingering showers.

The next in a series of progressive storm systems is approaching
the Aleutians. A leading warm front is leading to quickly warming
low level temperatures, with rain overspreading the western and
central Aleutians.

&&

.MODEL DISCUSSION...
Models remain in good agreement and forecast confidence is
generally high over the next couple days.

&&

.AVIATION...
PANC...In the wake of today`s snow, there may be some localized
areas of fog or stratus (IFR conditions) in the vicinity of the
terminal. However, with increasing low level flow this evening it
does not look favorable for anything widespread or long-lived to
develop. Thus, have trended toward VFR conditions this evening.
The low level winds will weaken by Sunday morning, so will have
to watch for fog formation if we begin to cool down under clear
skies. For now, that is a low probability possibility and have
stuck with VFR conditions through Sunday afternoon.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A drying trend will continue overnight as leftover snow flurries
and showers come to an end. This will be in response to increasing
weak cold air advection and dry northwesterly offshore flow. A
strong upper jet will also continue to support strong westerly
offshore through southern Cook Inlet into Homer and Kodiak Island.
Sunday will be dry and quiet with attention quickly turning to
another low which will move into Cook Inlet from the west. This
will bring another shot of snow to Southcentral Sunday night
through Monday night. Currently, this snow event is looking to be
a more typical distribution which will favor the west facing
slopes of all the high mountain ranges. With rather high snow
ratios and favorable dynamics, this snow event may reach close to
advisory level snow amounts (although over a 24 hour period) for
some locations from Anchorage north to the Matanuska Valley. Snow
will quickly taper off Monday night, lingering longest near the
mountains.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2: Sunday and
Monday)...
Quiet weather is returning to Southwest Alaska for another brief
time between systems as weak high pressure moves over the area.
With onshore flow over portions of Bristol Bay, especially from
King Salmon south and through the Kuskokwim Delta, patchy dense
fog is possible in some areas tonight. Then on Sunday, the next
system moves into Southwest Alaska, as a portion occluded front to
the north, and warm front to the south, with the parent low
remaining over the Bering. This will bring yet another round of a
few inches of snow to all of Southwest Alaska overnight Sunday
night. For the upslope mountains, which will be the west sides of
the Kuskokwim and Alaska Ranges, amounts closer to a foot are
expected with this latest round of snow. Colder air moves in on
increasingly strong west to northwest flow during the day Monday,
resulting in an anti-diurnal temperature trend with the high
temperatures for the day expected early in the morning, then
falling throughout the day into Monday night. Because of the
strong northwest flow, snow showers will continue in the mountains
through much of the day, potentially continuing through much of
Monday night, since the flow off the Bering is expected to be
well-modified with moisture.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2: Sunday
and Monday)...
A strong area of low pressure is moving into the western
Aleutians this afternoon. It is bringing another round of warm air
east of the low`s center. The most hazardous weather associated
with the low will be after the center passes and the colder south
and west side of the low moves into the area. Very strong winds on
cold advection are expected tonight across the western and
central Aleutians. Fortunately, the low itself is not expected to
get very strong, only getting to about 980 mb at it`s strongest
point during the day Sunday. Thus, only occasional gusts to
hurricane force are expected along the Aleutians late tonight into
Sunday, though sustained winds to storm force (50 kt) will be
more widespread. The low will track generally eastward into the
Kuskokwim Delta Sunday night. With dynamic fetch (waves moving in
the same direction as the storm`s center for a long period of
time) expected on the south side of the low with the stronger
winds, look for seas exceeding 30 feet between the Aleutians and
the Pribilofs into Sunday night.

Once the low moves into Southwest Alaska, conditions will calm
down somewhat, with a much weaker low moving into the western
Aleutians late Sunday night into Monday morning. This weak low
will slowly track eastward through the central Bering through
Monday night, but no hazardous weather is expected from it.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The progressive pattern with zonal westerly flow will continue
Monday night into Tuesday with a couple more cold troughs tracking
across southern Alaska. West to northwesterly outflow will
increase across Southcentral Alaska and the western Gulf Monday
night following the passage of one trough. The next trough,
bringing additional cold air aloft with it, will swing into
Southwest Alaska Monday night and continue into Southcentral and
the Gulf Tuesday with another small shortwave following through
the northwesterly flow aloft late Tuesday night through Wednesday
morning.

Further out to the west, a rapidly deepening north Pacific low
will track north towards the western Aleutians on Tuesday and
then cross into the western Bering Tuesday night and Wednesday.
With the low still strengthening as it passes not far to the west
of Shemya, storm force or stronger winds are likely. In response
to the deepening storm, a strong upper level ridge will build over
the central Bering Tuesday and then continue to amplify as it
shifts east over the eastern Bering Tuesday Night and west coast
of Alaska Wednesday.

Forecast confidence decreases rapidly Friday through the weekend
due to uncertainty in how fast the large ridge will push east and
in what manner it will break down. Models, however, do agree on
general trend back towards active zonal flow for the first half of
next week.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm Warning 130 131 136 137 165 170 173 175 177 178.
 Gale Warning 120 132 138 139 141 150 155 160 171 172 174 176 179
180 185.
 Heavy Freezing Spray 181.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
LONG TERM...JR



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