Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 082254 CCA
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
154 PM AKST Fri Dec 8 2017

.ANALYSIS AND UPPER LEVELS...
The remnants of the low that brought rain and snow to much of the
South Mainland on Thursday is beginning to slowly weaken as it
makes landfall. Over the Gulf, a weak low that developed under the
deep southerly jet is beginning to bring widespread rain to much
of the Gulf coast northward into the Copper River Basin. The good
news for Gulf Coast is that a break in the widespread
precipitation that has plagued the area for much of the week is
beginning to move northward through the Gulf and should bring
improving conditions by this evening. Just to the west, clearing
skies with a very moist boundary layer is allowing for low
stratus/patchy fog to develop around Cook Inlet northward into the
Susitna Valley, which has been dense at times already this
morning over the Anchorage Bowl. Over the Southwest mainland, a
weakening upper trough is bringing one last round of snow showers
from Bristol Bay into the Kuskokwim Delta as it tracks northward
into the western interior. One last low is located just south of
the AKpen, which will also track northward along the jet today and
bring rain/snow to the AKpen by this afternoon.

&&

.MODEL DISCUSSION...
The models remain in generally good agreement into Saturday with
both the low south of the AKpen and its associated trough moving
through the Gulf, as well as the storm force front moving through
the Western Aleutians on Saturday. Starting Sunday, the models
begin to break down with regards to the timing of an intensifying
low that will quickly move from the Gulf into the Southwest
Mainland. There is however good confidence that this low will
bring widespread gale-storm force winds as well as strong gap
winds along the gulf coast at some point Sunday-early Monday, but
exactly when will still need to be determined once model agreement
improves.

&&

.AVIATION...
PANC...Expect LIFR conditions from areas of low stratus and dense
fog to continue drifting around the Upper Cook Inlet region this
morning, producing highly variable conditions from LIFR to VFR
with fog in the vicinity of the airport through mid morning. The
fog should mostly diminish by mid-late morning, however low
stratus is expected to remain near the area into this afternoon
when ceilings should improve to around 5000 ft. Fog and low
stratus is then expected to redevelop late this evening with
continued stable conditions and light winds.

&&

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

Precipitation is slowly diminishing from the west across
Southcentral today. Rain at the lower elevations and Snow at the
higher elevations along the North Gulf will be slowly diminishing
through today. Areas of rain and freezing rain will likely linger
into the afternoon hours over the eastern/southeastern Copper
River Basin this morning, so we have extended the Winter Weather
Advisory accordingly. Areas of low clouds and patchy fog will
likely linger across Cook Inlet, Anchorage Bowl, and portions of
the Mat-Su Valleys into the early afternoon hours. We may see a
little again tonight, especially over the Anchorage Bowl and along
Cook Inlet.

Another surface low with a frontal trough heads northwest toward
Kodiak Island/North Gulf Saturday. These systems will bring
another round of warm, windy, and wet conditions. The brunt of the
precipitation looks to be along the coasts with downslope
mitigating precipitation west of the Kenai and Chugach Mountains.
Thankfully, there should not be a deep moisture fetch with this
system, so we are not expecting unusually high QPF values.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Another shortwave lifting north up the Southwest Alaska coast is
bringing rain and snow showers to the greater Bristol Bay area
from King Salmon west and snow showers to the Kuskokwim Delta.
Further east along the west slopes of the Aleutian and Alaska
Range downsloping and breezy easterly winds are keeping
conditions drier. Another trough will rotate across the Alaska
Peninsula this afternoon and an associated front swinging across
Bristol Bay though mostly staying offshore this evening.
Meanwhile an east to west running upper level ridge will amplify
over the lower Kuskokwim Valley and Kuskokwim Delta while an upper
low persists south of the Alaska Peninsula. The next easterly
wave will cross from the western Gulf into Southwest Alaska
Saturday night through Sunday morning with a significantly
stronger frontal system tracking up from the southeast Sunday
afternoon and evening.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
An area of northwesterly winds of 30 to 35 knots over the western
Bering along the east side of an upper level ridge building into
the western Aleutians, will shift east over the central Aleutians
tonight as the upper level ridge amplifies and slides east as
well. A strong frontal system bringing storm forces southeasterly
wind will approach the western Aleutians Saturday. The front will
stall stretched across the western and central Aleutians Saturday
night and then weaken quickly as it shears apart and drops back
down to the south.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long-range forecast through the middle of next week continues
to depict an essentially unchanged overall weather pattern. The
very strong ridge of high pressure over western North America
looks like it will generally hold strong between now and then.
This will continue to steer numerous weather systems from south to
north through the Gulf of Alaska, which will result in additional
multiple rounds of heavy rain along the Gulf coast (and heavy
snow in the mountains) for the next week. The storm moving through
this pattern on Sunday night/Monday continues to look like it
will be pretty strong, with a storm-force weather front slamming
into the coast. Once again there will be a deep subtropical
connection with this storm, and impacts from heavy rain and snow
will need to be monitored.

Meanwhile, the Bering Sea and Aleutians will remain unsettled but
mostly benign during the forecast period, as the deep longwave
trough keeps most of the storms to the east (in the Gulf of
Alaska). By the end of next week in the Thursday or Friday
timeframe there is starting to be some indication that more active
weather will shift back into the Bering Sea, which potentially
could be the first sign of a change from this pattern featuring a
highly amplified ridge in the eastern Gulf/Panhandle.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 141.
MARINE...Storm 178
         Gale 119 125 130 131 132 138 172 173 174 175 176 177.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...DEK
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...AMD



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