Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 241604 CCA
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
512 AM AKDT Mon Jun 24 2019

.ANALYSIS AND UPPER LEVELS...

The synoptic pattern features a mature low pushing across the
Aleutians. Looking at the latest ASCAT (Advanced Scatterometer) data,
the surface low is northeast of Adak with the occlusion in the
Bering and a cold front in the North Pacific. There is a ridge
east of Bristol Bay. High pressure aloft has set up over the
interior of Alaska, which has resulted in widespread above normal
temperatures. Yesterday, a daily record was set at Ted Stevens
Intl Airport with a high temperature of 78 degrees. The previous
record of 75 degrees was set back in 1974. Talkeetna also tied its
record for max temperature for June 23rd at 84 degrees.

&&

.MODEL DISCUSSION...

For initialization purposes, radar imagery was compared to
yesterday afternoon and evening to where the models suggested it
would form. The NAM and GFS did well over the Copper River Basin
and Susitna Valley, but the Kenai Peninsula did not get
thunderstorms as advertised. Big picture wise (a.k.a. the synoptic
pattern), the global models are in good agreement over the
Bering, North Pacific and across the southern tier of the state
through Wednesday. The NAM and GFS are still pinging into
convective initiation for the Kenai Peninsula, Susitna Valley and
Copper River Basin again this afternoon. It is possible that with
the shift in upper level flow, and with the smoke blanketing the
Kenai, it may inhibit thunderstorm development over the Peninsula,
but the models are once again showing afternoon thunderstorms.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist. Looking at raw
satellite imagery, the HySplit model and the NESDIS (National
Environmental Satellite Data and Information Service) smoke
products, it would appear that the smoke from the Swan Lake Fire
will stay away from the PANC aerodrome this TAF package. Isolated
thunderstorms will develop north and east of PANC, but the
current thinking is that they will not move over the PANC.
Amendments will be made if needed.

&&

.FIRE WEATHER...

Southcentral is experiencing above normal temperatures. The heat
wave will continue this week. The past several days, the minimum
RH has been ranging from the 40s-50s with a few locations dipping
below 40 percent. With the ridge holding steady, and actually
amplifying by mid-week, expect the min RHs to decrease and the
nocturnal recoveries won`t be as strong. Convection is still in the
picture, but the greatest confidence of them forming will be over
the Copper River Basin. Southwest AK will be dealing with the ridge
and the above normal temperatures also. The convective signatures
don`t look as good in the models for those FWZs.

&&

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

Ridging will be the dominant weather influence for the beginning
of the work week bringing warm and dry conditions with light
winds. Coastal area winds increase each afternoon as sea breezes
develop...which then taper off during the evening. Thunderstorms
during the afternoon and evening are expected to develop along a
weak boundary that stretches from east to west across the Copper
River Basin to the Susitna Valley. There is also an isolated chance
for thunderstorms across the Chugach and Kenai Mountains during peak
heating; however, this potential will be greatly limited by
decreasing moisture in the mid levels around the ridge.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Wednesday Night)...

A quiet day is expected today in Southwest Alaska under a
building upper level ridge. This should allow for more of the area
to get well into the 70s, with an 80 degree reading or two in the
Lower Kuskokwim Valley not out of the question. Tonight, a
disturbance and associated front will move into the coast. This
will bring some scattered shower activity to mainly the Western
Capes and the Kuskokwim Delta. The rain threat will persist into
Wednesday for the Kuskokwim Delta. Thus, cloud cover should be
relatively abundant over most of Southwest Alaska, with the
exception of the Alaska Range foothills in the Lower Kuskokwim
Valley. Despite building ridging and warming mid-level
temperatures, the cloud cover should keep western areas relatively
cool and wet, as the warmest temperatures stay along the Alaska
Range. This pattern is not conducive for much of any thunderstorm
activity most anywhere in Southwest Alaska, with only a slight
chance of an afternoon and evening thunderstorm in the Alaska Range.

&&

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

The large, weak low over the western Bering is expected to
continue slowly moving northward through Wednesday, with a faster
northward movement towards the Kamchatka Peninsula during the day
Wednesday. As is very typical for summertime in the Bering, there
is widespread low stratus and fog over the entire basin, so the
biggest forecast change was to add fog wording to the forecast
over large swaths of the Bering. As the low moves north, it`s warm
front over the central Bering will slowly drift eastward towards
the Alaska coast, but will bring a prolonged period of small craft
southerly winds through the eastern Aleutians, along with some
rainfall. Winds could locally approach gale force through the
gaps in the eastern Aleutians.

&&

.MARINE (Days 3 through 5)...
(Wednesday through Friday)

...Bering Sea and Aleutian Coastal waters...

Fairly benign conditions will exist for the middle of the week
towards the weekend, as a weakening front stalls across the east
central Aleutians. There may be a brief window for some very low
end gales to develop near the eastern Aleutians into the tip of
the peninsula, but confidence in this materializing is mediocre at
best.

...Gulf of Alaska...

Minimal marine impacts are expected from the weather, as a ridge
of high pressure will encompass much of the region. This will help
promote offshore flow, which may increase winds into Small Crafts
near the coast. Otherwise, look for this pattern to hold into
next weekend.

&&

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

Forecast uncertainty is fairly high for the middle of the week
through the weekend, as the omega block that is currently in
place tries to break down as an area of low pressure across the
western Bering bumps into a shortwave ridge centered from the
North Pacific, through Southcentral, peaking near Fairbanks. This
ridge is then flanked by a downstream low near the Pacific
Northwest.

As is typically the case, the model agreement on how fast this
ridge breaks down is not that good at all, with the GFS being the
biggest outlier compared to the ECMWF and Canadian Hemispheric
models. Given the strength and persistence of the ridge, prefer a
slower breakdown of this feature with the initial energy across
the Bering being deflected either to the north, as it rounds the
top of the ridge, or south into the central Pacific. This would
yield a continued warm and dry pattern for Southwest and
Southcentral, with seasonal temperatures and light winds from the
central Bering and Aleutians eastward towards the mainland coast.
That in turn keeps the unsettled weather located across the
western half of the Aleutian Chain and Bering Sea.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JPW
MARINE/LONG TERM...PD



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