Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 240057
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
457 PM AKDT Sat Mar 23 2019

.ANALYSIS AND UPPER LEVELS...

An active weather pattern continues for the weekend across the
state. An upper level jet over the Bering is helping to drive a
front associated with a Kamchatka low eastward. This occluded
front continues to bring rain and low level stratus over the
central Aleutians, while ahead of this front, a weak ridge has
attempted to build over the eastern Aleutians. Looking on the
backside of the Kamchatka low, satellite imagery confirms areas
of open- cell cumulus beginning to fill in behind the low,
indicating the start of a cold air advection regime over the
western Bering.

Looking eastward, a ridge over the Yukon still maintains its hold
over much of the Mainland, however a weakening frontal boundary
associated with a dissipating surface low over Bristol Bay still
extends across Southcentral. As a result, surface observations
and radar data both confirm scattered showers moving from the
southeast to the northwest across Southcentral.

&&

.MODEL DISCUSSION...

Models remain in good agreement through the next 48 hours. By Sun
evening, all model solutions indicate a North Pacific low
entering the Bering.

&&

.AVIATION...
PANC...Generally VFR with light rain with a possibly of brief MVFR
conditions this evening. Southeast winds across the airport
complex will diminish Sunday morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A weakly organized surface low and front currently moving across
the Northeast Gulf pushes slowly inland from the western Prince
William Sound late this evening. This will bring scattered rain
chances along and north of Whittier...with a few inches of snow
for elevations above 2500 ft. Easterly gusts will also increase
along this front for typical east to west oriented gaps. Another
low pressure system moving to the southern gulf tonight keeps
chances for rain and snow through Sunday along with gusty winds
before tapering off Sunday night as ridging builds across from
the southwest mainland. Skies should start clearing Monday night
allowing temperature trends to go back to a freeze thaw pattern to
start the week.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Tonight
through Monday Night)...

A warm pattern continues across Southwest Alaska tonight as broad
southerly flow over the area keeps a feed of increasingly warmer
air moving through the region. The remnants of a dying front are
helping keep low clouds and some fog persisting along the
Kuskokwim Delta coast. The warm air moving over the sea ice will
also keep temperatures significantly cooler there than areas
further inland. Tonight, some fog may develop from Bethel westward
due to the ice cooling the warm, moist air mass.

Late tonight, a weakening gale force front will move into the
Kuskokwim Delta, causing rain to spread inland from west to east,
reaching Bethel Sunday morning. The front rapidly dissipates
during the day Sunday, so the windiest period will be Sunday
morning. Further east, southerly breezes will develop, but little
precipitation is expected to get east of the Kuskokwim Mountains,
other than some upslope on the east facing slopes. The front will
keep the skies mostly cloudy, however.

On Monday, as a strong low wraps up over the western Bering, it
will draw even warmer air into the area. It wouldn`t be surprising
if a number of locations crack the 50 degree mark Monday
afternoon, especially in the sunnier locations along the Alaska
Range. Any downsloping should only help to further warm
communities along the Alaska Range such as King Salmon and
Iliamna. The associated cold front will have a hard time making
much eastward progress with a strong ridge of high pressure and
warmer air further east. It will reach the Kuskokwim Delta Coast
during the day Monday. The front will slow to a drift by Monday
night, as it quickly weakens so most areas from Dillingham east
will stay dry through Monday night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Tonight through Monday Night)...

A weakening occluded front stretches across the central Bering
this evening, approaching the Pribilof Islands. The front will
quickly move northeastward, reaching the Kuskokwim Delta coast
late tonight. The parent low, producing gales across the Western
Aleutians, is slowly moving north, so the gales will persist there
through the night and diminish on Sunday.

A second, much stronger low will track further south and east than
the current one. It is expected to track northward, crossing the
Aleutian chain between Adak and Shemya Sunday night. Unlike many
other lows, this one is expected to still be strengthening when it
crosses the Aleutians. Thus, the low is expected to produce
hurricane force wind gusts after midnight Sunday night from Atka
westward to about the Date Line, including Adak. Fortunately,
since it will be tracking straight north, no other land areas will
be impacted by the core of the strongest winds once it clears the
Aleutians by Monday morning. Gale force winds and high swell will
continue eastward across all of the rest of the Aleutians, the
Pribilofs, and the Kuskokwim Delta Coast with the leading front on
Monday. Once the low reaches Kamchatka Monday night, small craft
southerly winds will continue across a large portion of the
central and eastern Bering into Tuesday morning.

&&

.MARINE (Days 3 through 5)...

Gulf of Alaska... Expect generally benign conditions, with winds
diminishing and seas subsiding as pressure builds.

Bering Sea... Winds will diminish and seas will subside Tuesday as
the former storm force low continues to fill and shift northward.
Then, expect generally benign conditions, with one small caveat. A
low currently roughly 800 miles off the coast of Japan will track
northeastward through Thursday. Its expected trajectory is highly
uncertain, and it`s possible that it will track far enough east to
bring gales to the western Aleutians and Bering Sea Thursday.

&&

.LONG TERM FORECAST (Days 4 through 7)...

Confidence remains high that the long term period will begin with
an upper high over Southcentral that will slowly drift eastward,
and with a low upstream moving from the northern Pacific eastern
Siberia. Thus, expect dry weather, warm afternoons, and
relatively cold nights driven by limited cloud cover over
Southcentral and the Southwest mainland. That said, with ample
surface moisture and atmospheric stability, there will also be
potential for morning fog, especially in Southcentral which could
decrease the diurnal temperature range. Farther west, a shortwave
trough will bring a brief round of precipitation and south winds
from west to east Wednesday, likely fizzling before reaching the
AKPEN.

Forecast uncertainty increases substantially Thursday. The
aforementioned low will either shift towards the Sea of Okhotsk,
or take a more eastward track towards the Kamchatka Peninsula.
The latter track would yield a wetter, windier pattern for the
Aleutians...and which progression actually occurs will depend on
what happens upstream, i.e., how far east the high over
Southcentral shifts. Unfortunately, models have little consistency
between runs, between models, and between ensemble members. So for
this forecast package, continued a blend with pops slowly
increasing from western Aleutians towards the AKPEN through
Saturday. Be sure to monitor the forecast as it will probably
change over the coming days.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storms 175-177 413 Gales 165 170 172-174 178-181 185 411
412 414.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...KO/DS
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
MARINE/LONG TERM...MM


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