Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 291229
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
429 AM AKDT SUN MAY 29 2016

.ANALYSIS AND UPPER LEVELS...

Mid- and upper-level high pressure remain entrenched across
western Alaska this morning. A large, multi-faceted upper low
resides over British Columbia, with a second, smaller system
located over the eastern Gulf of Alaska. Additional upper lows
reside out west, with a low over the southern Bering and North
Pacific near the Central and Eastern Aleutians, and another low
extending from Kamchatka to near the far western tip of the
Aleutian chain.

The upper level jet stream is quite active across Alaska and
Bering. A strong northerly jet streak persists on the downstream
side of the upper high across the entire eastern two-thirds of the
Alaska mainland, stretching from the North Slope to the Gulf of
Alaska. A fairly strong southeasterly jet also persists on the
upstream side of the high, extending from the North Pacific south
of the Alaska Peninsula through the central and northwestern
Bering into northeast Russia. The strongest jet streak, however,
is a southwest jet well south of the Western Aleutians that is
moving in the general direction of the Central Aleutians.

With strong northerly flow in the mid-levels over Alaska, as
expected there is a low pressure trough along the northern and
northeast Gulf coast, and extends west across the upper Cook Inlet
region into the Southwest mainland. A weakening 994 mb low is
located northwest of Attu and is moving toward Kamchatka. The most
notable feature, however, is a strengthening 987 mb low located
about 600 miles south of Attu, and is associated with the
aforementioned North Pacific jet streak moving in the general
direction of the Central Aleutians for Monday and Tuesday of this
coming week.

&&

.MODEL DISCUSSION...

Models are generally in good agreement with the synoptic pattern
through Tuesday. The main challenge across the southern mainland
today is the timing and phasing of a rather strong easterly wave
from Canada and a pronounched mid-level jet streak rounding the
high over Northwest Alaska. Bottom line, the result will be
critical fire weather conditions for inland areas from the
Kuskokwim Delta east to the Susitna Valley today with increased
winds, and increasing shower and thunderstorm potential to the
south and east from the Copper River Basin and Susitna Valley to
the Kenai Peninsula to eastern areas of inland Bristol Bay,
especially along the Aleutian and Alaska ranges.

For the Bering and Aleutians, the main focus shifts to the
developing storm system in the North Pacific which quickly moves
to the Central Aleutians Monday into Tuesday. By Tuesday, the EC
is an easterly outlier by about 100 miles with placement of
surface low pressure near the Central Aleutians. Though the EC has
am excellent track record the last few days across the entire
region, it is a distinct outlier with respect to this system with
no support from any other model. The forecast largely follows the
model consensus minus the EC model toward the Central Aleutians.

&&

.FIRE WEATHER...

Extreme fire weather conditions due to strong northerly winds are
expected during peak heating of the afternoon and evenings across
the southern mainland today from inland Kuskokwim Delta east into
the Susitna Valley.

One troubling trend to note in the models over the last 12 hours
or so is that almost all models are becoming more aggressive in
shower potential from the Talkeetna Mountains south along the
Chugach and Kenai Ranges late this morning and afternoon. The
impetus for this more bullish trend appears to be increased
frontogenesis in the lower to mid-levels through this area, with
increasing moisture provided by the Gulf as the decently strong
easterly wave approaches. Thus, revisions upwards in shower
coverage along the Chugach and Kenai Ranges east of the major
population corridors may be needed by this afternoon.

Toward the Susitna Valley, the disturbance is likely to move
overhead during afternoon peak afternoon heating and with pretty
strong dynamics in place with an intruding dry slot aloft
coinciding with the left-exit region of the mid-level jet streak.
Thunderstorm activity may thus exceed current meager expectations
over the Susitna Valley for late this afternoon and early evening.
With fairly fast propagation of storms west and dry low-level air
in place, any potential thunderstorms are likely to be high-based
and on the drier side of things. This will bear close watching,
especially given the warm and dry conditions of the last few days.

&&

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

As mentioned in the fire weather section, confidence is low but
increasing that shower coverage from the Talkeetna, Chugach, and
Kenai mountain ranges may be more robust that initial
expectations. Additional uncertainty lies with the potential for
thunderstorm development over the Susitna Valley late this
afternoon into early evening given the impressive dynamics aloft.
Additionally, isolated to widely scattered thunderstorms are also
expected across much of the Copper River Basin today. Meanwhile,
to the south of the trough along the mountains, onshore flow is
likely to allow for the marine layer to move inland, especially
along the immediate Gulf coast and during the morning hours.

Southeast flow increases Monday as the thermal trough moves west
and north away from the area. Scattered showers and isolated
thunderstorms are possible, with the best chances for lightning at
present looking to be along the Talkeetna Mts. and the Kenai
Range.

&&


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

Very warm and dry conditions are expected today ahead of an
easterly wave coinciding with a northeasterly jet streak moving
into the region from the Interior. From the southern Alaska Range
south along northeastern sections of Bristol Bay, the easterly
wave will induce scattered showers and isolated thunderstorms.
These showers and isolated thunderstorms will then spread
throughout the southwest mainland on Monday as a shortwave moves
through.

&&

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

The focus is beginning to shift to a Northwest Pacific low that
will increase winds to gale-force as it moves into the
Central Aleutians on Sunday. Model agreement is improving on the
track of this low, allowing gale-force winds and higher rain
probabilities to be added to the forecast for most of the central
and eastern Aleutians into Monday.

&&

.LONG TERM FORECAST (Tuesday through Saturday)...

The dominant high pressure center creating warm and dry
conditions across the mainland will slowly retreat to the west
through early next week. This will allow increasingly cyclonic
flow to enter the Gulf of Alaska and southern Mainland during the
week. At this point it looks likely that the most active weather
will stay far enough out to sea in the Gulf that most of the area
will see fairly good amounts of sunshine continuing, though
diurnal shower (and maybe thunderstorm) activity will slowly
increase throughout the weak. Meanwhile, the Bering Sea and
Aleutian region will remain generally under the influence of high
pressure and strong low-level inversions that keep fog and stratus
a persistent problem. This large-scale weather pattern is very
typical for this time of year, and as such temperatures and
sensible weather should follow suit and be fairly close to
climatology for temperatures and precipitation across the forecast
area next week.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales...170 172-178.
FIRE WEATHER...Red Flag Warning...145 153 155.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...CC
FIRE WEATHER...CC
SOUTHCENTRAL ALASKA...CC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK/CC
LONG TERM...AD



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