Area Forecast Discussion
Issued by NWS Anchorage, AK

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041
FXAK68 PAFC 150038
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
438 PM AKDT Tue Aug 14 2018

.ANALYSIS AND UPPER LEVELS...
Two circulations are visible on satellite imagery today: one is
the last vestiges of the Pacific typhoon moving into Southcentral,
the other a deepening low quickly becoming the main weather
player another over the Southern Bering Sea.

While rain is spread around Southcentral again today, previous
waves of rain have brought some streams and rivers out of their
banks. Montana Creek is in minor flood stage at the Parks Highway
and is expected to improve shortly. The Yentna River at Lake Creek
is worsening with flood waters into area cabins and a crest
expected by early Wednesday morning before waters recede. Stay
tuned to Flood Warning information for more.

In general, most 24-hour rainfall reports have been under one-half
inch. Of course there are always exceptions. Today these include
the Independence Mine area with a 24-hour 2-inch report by midday
and the Kwethluk / Crooked Creek region with reports in the
2-inch range over 24-hours as well. Nothing like an early start to
Autumn in Southcentral.

.MODEL DISCUSSION...
Models have not been resolving the pattern with any great success
or agreement as seen on 0z and 6z initializations with the Bering
Sea upper low out of whack by over 350 miles. Hope, like Summer,
is fleeting. With that, the forecast team has singled out the NAM
as the most `odd man out` and will rely on the GFS for both East
and West domains. We should expect that as the remnants of the
typhoon are finally extinguished, models will focus on the
remaining circulation and yield more confidence.

&&

.AVIATION...
PANC...Clouds and rain will continue through the vicinity, however
improving conditions will become more routine in the next several
by late this evening. VFR is expected with occasionally gusty
winds this evening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Tonight through Friday)...
Shower activity will slowly diminish tonight as the upper level
trough over the area continues to weaken and move northeast. Most
of the precipitation will be in the Susitna Valley and
surrounding mountains, as well as areas along northern and eastern
Prince William Sound and the Copper River Basin east of
Glennallen. At the surface, the surface gradient will relax
tonight into Wednesday morning as the the upper trough weakens.
This will allow winds over the marine areas to diminish. On
Wednesday, a digging trough over the eastern Bering will lead to
development of a weak downstream ridge over Southcentral. This
certainly won`t be strong enough to end all precipitation, but
shower activity will be fairly minimal and there should be some
breaks of sun. An upper level low will move into the Gulf
Wednesday night and Thursday, for a modest increase in shower
activity.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Tonight through Friday)...
A tranquil period of weather is expected for Southwest Alaska for
the next three days. A small, but rather wound-up area of low
pressure developing off Nunivak Island right now will drift
southward off the coast of Cape Newenham Wednesday morning.
Localized small craft conditions are possible around the low, but
otherwise, it will be the focus for additional scattered shower
activity during peak heating Wednesday afternoon, particularly
along the coast through Bristol Bay. The rest of the area should
remain mostly dry, though an isolated shower can`t be ruled out
elsewhere. By Thursday morning, the weakening low will drift
southwestward away from the coast, though instability associated
with an upper level wave may be the focus for additional showers,
particularly the closer to the Alaska Range you go. An isolated
shower or two will be possible Friday as the region goes under a
surface col, resulting in calm winds. A larger, stronger low moves
north out of the Pacific, resulting in the next round of
widespread rainfall for Saturday. More on that below.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Tonight through
Friday)...
Northerly winds on the west side of the aforementioned
compact low will keep conditions breezy through the Pribilofs
down to the Alaska Peninsula on Wednesday. High pressure will
remain firmly anchored over the central Bering through Friday. The
low will drift south towards the southern Alaska Peninsula
Thursday and dissipate by Friday morning. Over the far western
Bering, a broad front will move into Attu and Shemya during the
day Wednesday. The parent low located west of the front will be
shunted south and east into the North Pacific as the high pressure
over the central Bering persists. A more consolidated low
develops south of Adak on Thursday, which will help dissipate the
rainfall over the western Bering Thursday night. This will allow
the central Bering high to build westward through Friday. A strong
low will develop over the north Pacific well south of Kodiak on
Friday, and will become the primary weather-maker going into the
weekend.

&&

.LONG TERM FORECAST (Friday night through Tuesday)...
The long term beginning Friday night starts with a North Pacific
low sandwiched between two ridges. The first ridge will be over
the eastern Gulf while the other is over the central Bering. There
is some discrepancy between the models on the exact position of
the low and subsequently its front, but the general consensus is
that the front will bring rain to the Alaska Peninsula and Kodiak
Island Friday night. Through the weekend the system will slowly
track north spreading rain to the southern Mainland with the
heaviest amounts along the north Gulf coast and Alaska Peninsula.

Meanwhile out west, another system will push into the Bering over
the weekend as the central Bering ridge breaks down. Early next
week the upper level low centers of the two main lows look to
merge into a broad area of low pressure over the Bering with
ridging off to the east. This setup would keep a rainy pattern
for the region into mid next week.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Warning 145.
MARINE...Gale 138.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...DJS
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
LONG TERM...DK



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