Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 211457 CCA
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
417 AM AKDT Fri Jun 21 2019

.ANALYSIS AND UPPER LEVELS...

The synoptic pattern features a ridge of high pressure spanning from
southeast Alaska north into the interior. South of Kodiak there is a
mature low with a front extending into the Gulf of Alaska and
Pacific. Many locations in south central Alaska reached the 70s
yesterday but some of the coastal locations were socked in with fog
and stratus. Yesterday, the max temperature at the Kenai Airport was
54F which was actually lower than Deadhorse`s max temperature of
58F. Looking west, there is another dome of high pressure over the
central Aleutians and a new low in the North Pacific which is
southwest of Shemya.

&&

.MODEL DISCUSSION...

The global model guidance is in good agreement with the synoptic
features through Tuesday. There are differences with convective
parameters and potential thunderstorm development for south central
Alaska. The NAM is being more aggressive with the instability as
usual. But the real concern is with the distribution of the cloud
shield associated with the low south of Kodiak. This cloud coverage
will impact diurnal heating which will impact instability. There are
some weak shortwaves getting kicked out of the low and moving across
south central Alaska which would support thunderstorm development.
There is some uncertainty about temperatures and thunderstorm
potential.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist.

&&


.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Warmer and mostly dry conditions settle across south central Alaska
Friday and Saturday as ridging across the interior vies for
dominance against the low over the Gulf of Alaska. However, there
will be diurnal showers and thunderstorms across the mountain ranges
generally north of the Chugach, with a few storms possible across
the Matanuska Valley and Copper River Basin today. The front
currently across the southern Gulf of Alaska slowly diminishes
tonight as the associated surface low tracks east through Saturday.
Gusty small craft winds along the frontal boundary taper down this
evening.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
With unstable conditions over southwest Alaska, showers are
expected to develop this afternoon with a chance of thunderstorms
near the Alaska Range. Shower activity will diminish overnight
tonight before redeveloping Saturday afternoon. The areas possible
for thunderstorms on Saturday will widen to encompass the Middle
Kuskokwim Valley and areas around Bristol Bay. Showers will then
diminish Saturday night and redevelop Sunday afternoon while
southwest Alaska stays under an unstable pattern.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
As ridging over the western Bering pushes off to the east, a North
Pacific system is approaching the western Aleutians. By this
afternoon its associated front will bring rain to the Aleutian
islands and then it will continue to track to the north and east. It
looks to make it to the central Aleutians on Saturday where its
easterly progress will slow down as the system weakens. Sunday night
the slow moving front will make it to the eastern Aleutians.

&&

.FIRE WEATHER...

There is a low southwest of Kodiak that is pushing into the Gulf of
Alaska and this is going to cause a pattern change for the Kenai
Peninsula. Expect more clouds, lower temperatures and an increase in
RH. The wind direction will transition from up inlet flow to down
inlet flow by Sunday. And the ridge is going to get pushed east and
north. Interior fire weather zones will still be warm with thermal
troughs developing at the surface. The potential for thunderstorms
will remain through Saturday.

&&

.MARINE (Days 3 through 5)...

Beginning the longer term marine forecast on Saturday, the storm
track will be shifting west over the western Bering Sea as a gale
force low moves in Saturday, then lifts north and weakens through
Monday. While the strongest winds will remain over the western
Bering/Aleutians, there will be longer fetch southerly winds which
will bring some higher seas as far east as the Pribilof Islands.
Dutch Harbor may see a brief period of gusty southerly winds as
well. Otherwise, the eastern Bering Sea will remain quiet with sea
stratus/fog and generally lighter winds.

A departing low will be replaced by light west winds over the Gulf
of Alaska Saturday through Monday, with high confidence that no
storms or strong fronts will be anywhere near the Gulf of
Alaska/North Gulf Coast.

&&

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

There is no change in the overall thinking of the extended period
forecasting beginning Saturday evening as an interior ridge builds
as a Gulf of Alaska low departs to the southeast. The Yukon interior
ridge will build west as offshore flow across south central Alaska
results in further warming through the weekend. Uncertainty still
exists from Tuesday through the remainder of the week as the global
numerical guidance continues to struggle with low amplitude
disturbances passing through the upper ridge. However, the signal in
the noise is with warm interior temps inland, this will be enough to
promote the potential for inland thunderstorms, mainly across south
central Alaska where the greatest instability will reside. The
timing of these low amplitude shortwave troughs is very uncertain at
this juncture, but any of these waves could spark off rather
widespread thunderstorms across parts of Southcentral (favoring
interior and the mountains) Sunday-Tuesday.

Farther west, a series of lows will be tracking across the Bering
Sea and sending clouds/more stable air into southwest Alaska as
early as Monday. Much uncertainty develops Wednesday as all the
global models (ECMWF/GFS/Canadian and their respective ensembles)
depict an impressive array of highly disparate solutions from high
amplitude ridging/warming over the interior with fronts passing into
the southern Mainland. These disparities arise from potential
northern stream influences from the arctic to storms moving into the
Bering Sea from the Pacific. For now, expect warm temps (above climo
across the southern Mainland) to last through Wednesday before
uncertainty grows. However, with that said, there is still a strong
signal that the warm period will persist through the end of the week
in most of the guidance (ensembles and statistical MOS).

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 177 178.
FIRE WEATHER...NONE.

&&

$$

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



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