Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 211355
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
455 AM AKST Sat Jan 21 2017

.ANALYSIS AND UPPER LEVELS...

A frontal band extends from the eastern Susitna Valley south
across the Anchorage area and Kenai Peninsula and through the
western Gulf. Several small waves have rippled north up this band
with the current one crossing the Kenai Peninsula early this
morning. Snow totals have been rather high along the southeastern
side the Kenai Peninsula where southerly flow is being
orographically enhanced as it comes in off of the Gulf and hits
the mountains and also convergences with the cold low level
offshore northerly drainage winds. Additionally, there is enough
instability associated with this system to have produced isolated
thunderstorms embedded in the snow along the coast near Seward.

Further north and inland, the snow fall has been continuing
steadily though generally more lightly. A strong high centered
over the Yukon Territory is keeping the band from progressing to
the east, while the arctic trough digging in over western Alaska
is holding it in place from the west. Over the central and
eastern Bering, cold north to northwesterly flow continues to
generate instability showers while a weakening frontal system
lifts north across the western Aleutians. A significantly stronger
Pacific frontal system is in the process of spinning up out near
40N 160E.

&&

.MODEL DISCUSSION...

Models are in excellent agreement regarding the powerful frontal
system and north Pacific low which will track across the Aleutians
and Alaska Peninsula this weekend as well as with other large
scale synoptic features. The smaller scale features within the
north to south running frontal band conveying moisture from the
Gulf into Southcentral Alaska remain more of a challenge with
model differences continuing regarding how long the frontal band
will last and how much more snow it will produce.

&&

.AVIATION...

PANC...IFR snow is expected to continue into this afternoon with
brief periods of LIFR possible during heavier snowfall. Snow will
begin tapering off late this afternoon and evening with conditions
gradually improving to MVFR and then VFR. Occasional Light snow
however will remain possible at time tonight into Sunday.

&&

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

A frontal system continues to provide forcing for light to
moderate persistent snow across the entire Kenai Peninsula,
Anchorage Bowl, and Matanuska Valley this morning. The heaviest
snow continues near Seward as persistent southerly flow is locally
enhancing snowfall and even supporting a few lightning strikes.
Uncertainty still remains on how long the front will support
snowfall across Southcentral, but snowfall intensity is expected
to begin to taper by this afternoon and evening as the frontal
system and associated surface low weakens and drifts eastward.
Snowfall amounts will vary widely, with the greatest amounts
expected to continue across the eastern Kenai Peninsula, while a
few more inches of fluffy snow are expected for the Anchorage
Bowl.

&&

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

Well below normal temperatures will continue across Southwest
Alaska through the weekend as a deep arctic trough remains
entrenched across the region. A strong warm front will begin
moving across Southwest Alaska on Sunday which will bring a chance
of snowfall to the Alaska Peninsula Sunday late afternoon and the
Bristol Bay area by Monday morning. Conditions across the Alaska
Peninsula (Cold Bay, Sand Point, King Cove and other locations)
will deteriorate through Sunday night into Monday as strong winds
combine with heavy snow on the leading edge of the frontal
boundary. Snowfall ranging from 3 to 6 inches looks quite likely
with some upslope locations on the Pacific coastline seeing
possibly double that amount. Winds on Sunday night will ramp up
quickly along the frontal boundary and strengthen to 40 to 50 mph
with gusts upward to 65 mph by late Sunday night. This will bring
very poor visibilities as snow and wind combine to reduce
visibility to one half mile or less. There is a decent chance that
some locations may experience blizzard conditions but confidence
is too low to issue any blizzard products at this time for the
Alaska Peninsula. However, a winter storm watch for a combination
of snow and blowing snow has been issued for Sunday evening
through Monday morning.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

The Bering Sea is currently experiencing the calm before the
storm today. A few cold air advection showers have persisted
across the central Bering Sea but as the arctic trough slides
eastward, the atmosphere should stabilize and make showers very
far and few. As of 12Z this morning, a 982 mb low near 40N 161E in
speeding northeastward toward the central Aleutian Islands. As it
moves toward the Aleutians today, it will undergo rapid
cyclogenesis and deepen to 952 mb by 12Z Sunday. This drastic
change in surface pressure will create a very potent front that
will push through the southern Bering Sea late tonight through
Monday. Models have been in great agreement with low placement and
timing which has created great confidence in the overall evolution
of the system.

A high wind warning will be in effect for the western Aleutians
late tonight through Sunday afternoon as hurricane force wind
gusts upward to 85 mph will be seen as cold air advection on the
back side of the low helps mix down winds from a potent low level
jet. A high wind watch has been issued for both the central and
eastern Aleutians as the front pushed through tonight and Monday.
Winds could gust as high at 80 mph across these locations. Confidence
in high winds over the central Aleutians is much less than the
eastern and western Aleutians as the low track takes it just south
of the central Aleutians which means strong winds gusts will be
short lived. A blizzard watch has been issued for the Pribilof
Islands Sunday afternoon through Monday afternoon as wind gusts as
high as 70 mph accompany 3 to 6 inches of snowfall.

&&

.LONG TERM FORECAST (Days 3 through 7)...

An upper level closed low is centered over the Central Aleutians
starting out next week. As this feature moves eastward the strong
meridional south to north jet streak tracks into the Southeast
Panhandle by Tuesday. This pattern continues through the the next
weekend as the longwave trough moves farther eastward. Meanwhile,
look for a warming trend with the southerly flow into the Gulf
extending through the Southcentral Alaska region. Therefore, the
temperatures in the aforementioned region rises above freezing due
from the warm air advection. This results in more moisture
streaming into the AOR with a wintry mix along the coastal
communities as the warmer temperature filter into the region.
While the interior sets up with a better scenario for moderate
snowfall in favored mountain regions. Meanwhile, the models are
struggling some with the complex low developing in the North
Pacific Ocean before tracking towards the Central Aleutians by
Monday. This system will bring warmer temperatures along the
Aleutian Chain, and the lower Bering, while the rest of the
Bering is influenced by easterly to northeasterly flow through
majority of next week. Since the jet stream remains south of the
Aleutian Chain the storm systems will continue to track along the
Chain before entering the Gulf of Alaska. The forecast confidence
remains average through next week.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 191.
         High Wind Watch 185 187.
         Winter Storm Watch 181.
         Blizzard Watch 195.
MARINE...Gale Warning 165 185.
         Storm Warning 155 170 171 172 173 174 175 176 179 411
           412 414.
         Hurricane Force Wind Waring 177 178 413.
         Heavy Freezing Spray Warning 127 130 138 160 165 180
           185 414.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...JER
SOUTHCENTRAL ALASKA...EN
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MC
LONG TERM...PD


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