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AFG Warnings  Issued: 06/20/2017 01:06:31 AM AST Click for text

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FXAK69 PAFG 220915

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
115 AM AKDT Thu Jun 22 2017

.DISCUSSION...Pleasant and seasonal summer time pattern to
continue over northern Alaska through the weekend. The 00z
model suite initialized well against the 00z surface analysis
and verified well against the 18z surface analysis.

Aloft at 500 hpa, a ridge continues to build over the central
interior and will continue to drift to the east to be centered
over the central Yukon Friday. A shortwave trough centered over
the Bering Strait continues to move northeast and will be
centered over Barrow Friday and will continue to move northeast
into the Beaufort Sea Saturday.

On the surface a 1005 mb low currently over the northern Chukotsk
Peninsula will continue to move north and east to be located over
Wrangel Island this evening and will continue to move northeast
into the Chukchi Sea Friday. Southwest flow ahead of the low will
bring a round of small craft southwest winds along the northwest
coast. Rough seas as well as elevated surf will develop along the
northwest coast Friday and Saturday. Periods of low ceilings and
fog will continue along the northwest coast. Drying south and
southwest flow to the east of Barrow will limit low clouds and
fog in these areas.

A weak thermal trough along a Arctic Village to Whitehorse line
will move slowly north today to be along the eastern Brooks Range
by Friday. Southwest winds along the west coast will bring low
ceilings, fog and scattered showers along the coast but mostly
clear and dry conditions will exist inland. The ridge aloft will
limit thunderstorm activity over much of the western and central
interior with isolated showers and thunderstorms possible over
the eastern Brooks Range.

Coastal Hazard Potential Days 3 and 4...Models have a 988 mb low
moving across the Chukchi Sea and Arctic that could produce some
high surf along the northwest Arctic Coast Friday night and


.FIRE WEATHER...Relative Humidity values across the state are
expected to remain above 25 percent in the Central and Eastern
interior, except for the Upper Yukon Flats and Upper Porcupine
River Valley where they may dip into the upper teens and low 20s.
In the Western Interior and West Coast values will generally be
in the 30s and 40s. Winds will remain below Red Flag criteria
across the forecast area. Temperatures across the interior will be
in the 70s, so near Red Flag conditions will continue today and
Friday for the central and eastern interior.


.HYDROLOGY...No concerns through the weekend.


Small Craft Advisory for PKZ210-PKZ220-PKZ225-PKZ230.

Brisk Wind Advisory for PKZ235.



FXAK68 PAFC 221228

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
428 AM AKDT Thu Jun 22 2017

An elongated, dirty, dirty ridge (lots of cloud cover within) of
high pressure sits over the southern mainland this morning. It is
definitely the odd-feature out, with no less than five low
pressure centers flanking it on all sides. The three closest
systems are all weak and dissipating, two over the northern Gulf
providing a stream of moisture along the coast, and another is
nearing the Bering Strait with a weak upper level front along the
coast. The other two are in the northwest and northeast Pacific.
Most of these features are aloft with generally high pressure at
the surface. Persistent convection over the Canadian Yukon will
keep mid-level clouds streaming into the ridge. Weak shower
activity exists in the northeasterly flow between the low/high
across the mainland, even in the overnight hours.

Out west, the marine layer is in full pulse-mode, surging inland
overnight before getting mixed out during the daylight hours,
which are plentiful these days. A gale-force front is swinging
over the Western/Central Aleutians.


Guidance remains pretty much in lock-step with one another in this
semi-blocked pattern. The major systems, which are well outside of
most of the area of responsibility, are well agreed upon. The main
differences around the mainland are placement of convective
precipitation the next couple days, however, the general theme is
keeping higher terrain as the focus.


The moist northeasterly flow aloft over Southcentral Alaska
remains again today, but there is generally less dynamic lift
so the areas of showers are less widespread over the region as
compared to yesterday morning.

At the surface, the light south to southwest flow will keep
moisture pumping into the area and areas of stratus packed up
along mountains near the coast and Cook Inlet.

The Copper River Basin and northern Susitna Valley remain unstable
and there remains a chance for a diurnal thunderstorm or two over
the next few days, but nothing very widespread is expected.



Onshore flow this morning with high pressure aloft is bringing a
layer of marine stratus clouds to the western Kuskokwim Delta and
fog over the Bristol Bay area. With little in the way of synoptic
forcing, most of the marine layer should burn off and retreat as
solar heating intensifies this afternoon. Once the clouds burn
off, it should be a fairly nice day over Southwest Alaska before a
shortwave trough moves in tonight. The latest model runs have
been keying in on this feature, which will drop down from the
Bering later today and stall over the Kuskokwim Mountains tonight
through Friday afternoon. Convergence in the lower levels
associated with a weak trough at the surface and low to mid-level
moisture moving in from the east will support rain over the
Kuskokwim Mountains. Most of the rain should taper off Friday
night as the upper-level forcing weakens and moves out of the



A ridge of high pressure over the eastern Bering will shift east over
the next couple of days. This will allow a gale-force front over
the western Bering to move to the central Bering and Aleutians
through Saturday. As it moves east, gale-force winds along the
front will weaken to small craft winds tonight. Showers associated
with the front will push east as well and linger over the central
Bering as the front stalls and dissipates Friday night.

Another front will enter the western Aleutians Friday night,
bringing another shot of rain and a swath of gale-force winds to
the southwest Bering.


.LONG TERM FORECAST (Days 3 through 7)...

The upper level low moving into the southern Gulf will not make it
as far north as previously forecast thus the weak ridge across the
interior will hold. As the upper low moves off to the east, the
upper ridge builds back over western Alaska Sunday and Monday. As
this ridges builds it will slide east as a strong upper low pushes
into the central Bering Sea late Sunday. Monday through Wednesday
we expect the upper low to retrograde back into the northwest
Bering Sea with a trough extending southeast across the Alaska
Peninsula into the southwest Gulf of Alaska.

What this means for the sensible weather is we expect a warm dry
weekend for the southwest mainland while the Aleutians and Bering
Sea will transition from the fog and stratus regime to the more
active cloudy rainy weather beginning Friday night. Cool and
cloudy conditions should extend into the southwest mainland for
the beginning of next week to mid week while the central Bering
Sea and Aleutians remain in the cloudy, wet, and windy weather.

Model agreement has remained consistent through the long term and
the national guidance remained heavily weighted toward the
operational GFS model guidance through the weekend. The EC is a
bit of an outlier as we head to Tuesday and WPC stayed the course,
heavily favoring the GFS for their solution.


MARINE...GALE 175 176 177 178.




FXAK67 PAJK 221340

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
540 AM AKDT Thu Jun 22 2017

.SYNOPSIS...Low pressure in the eastern gulf will dissipate this
afternoon allowing a ridge of high pressure to extend across the
northern and eastern gulf. A weather front advancing into the
central gulf Friday morning will push the ridge into the
Panhandle. Meanwhile low pressure persists across Canada.


.SHORT TERM...Thursday through Friday night...The low responsible
for the convective air mass that has affected Southeast Alaska
for days still churns but in an aged, decrepit state. Hence we
keep scattered showers going through the day in the hopes that
they finally end this evening for all areas. There have been some
breaks overnight between showers, but these have resulted in some
very low cloud decks occasionally forming and not any
quintessential fog. As the low ceases to exist tonight, a ridge of
high pressure assumes control, and conditions will be much more
conducive to patchy fog development Friday morning.

A front entering the central gulf Friday will shove high pressure
over the Panhandle. This will prima facie pump a warmer, more
stable air mass into the region. While we are currently
forecasting high temperatures of 5 to 10 degrees warmer on Friday,
it is concerning that models are seeming to slow the warming at
850 mb. With synoptic wind components very light, we should expect
mainly channel breezes to develop Friday, and this can limit
heating along immediate shorelines where the majority of our
communities are situated. Significant downsloping winds appear to
be absent as well. Nevertheless, MOS numbers are still buoyant.
Thus, we keep the numbers high at this time.

A chance of rain is reintroduced Friday night as the front nears
the coast. But because of the front`s negative tilt, the chance of
rain will remain generally confined to the outer coast at least
initially Friday night. We bring the chance of rain farther
inland on Saturday.

NAM was the primary model of choice, although elements of the GFS
and ECMWF came in handy. Confidence is good to average for the

.LONG TERM...Saturday through Thursday...As of 9 PM
Wednesday...Period begins with low pressure system in the S
central gulf and ridge axis over the panhandle. Models in decent
agreement with the low moving towards the central panhandle Sat
night into Sun before moving slowly inland Mon. Surface ridge is
progged to develop over the gulf early next week and push eastward
through mid next week. Model solutions diverge by mid next week
with high pressure pushing E as low pressure moves into the gulf.

This will result in increased PoPs Sat into early next week before
a drying and warming trend through mid next week. Inherited
forecast represents this well, but did increase E winds in Cross
Sound to advisory levels for about 6 hours as high pressure moving
E interacts with the low moving into the gulf.


.AVIATION...Scattered showers will cause some MVMC conditions
today from Haines south. These conditions should improve markedly
by this evening with shower activity ceasing and clearing taking
hold. Saturated conditions in Ketchikan, Petersburg, and Gustavus
have necessitated some morning IFR tempos for ceilings. Confidence
in impactful patchy fog early Friday morning at central/southern
TAF Sites is low enough to omit at this time.


.MARINE...With a low filling in the gulf and high pressure
ready to expand across the region, we expect light winds through
Friday. Thermally driven low pressure across Canada may at times
enhance southerly winds through northern Lynn Canal. A front
entering the gulf Friday will increase easterlies across the gulf.
Cross Sound will increase to small craft by Saturday.


.AJK Watches/Warnings/Advisories...




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