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000
FXAK69 PAFG 202318
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
318 PM AKDT Sun Aug 20 2017

.DISCUSSION...Long wave troughing remains centered over mainland
Alaska, with the 20/12Z showing the trough pattern consisting of
a 538 dm low located around 30 miles northwest of Anvik. A short
wave was rotating around the southern periphery of this low,
located at 12Z in the western Gulf of Alaska. A second low with a
534 dm low center was located near the High Arctic around 78.4N
167.5W. Upper level ridging was located over the western
Aleutians, which extends north through the western Bering and
eastern Siberia. A 565 dm low was located just south of the
Kamchatka Peninsula. At the surface, a 997 mb low was located 180
miles south southeast of Kodiak. A surface ridge of high pressure
extends from the north Pacific into the Bering Sea, extending
through northwest Alaska and through the Beaufort Sea. A weak 1002
mb low pressure system was skirting across the Siberian Arctic
Coast, around 145 miles southwest of Wrangel Island.

The 12Z deterministic models are in good agreement on the overall
pattern through the upcoming week, with long wave troughing
expected to persist over the state. Upper low near Anvik will
drop south across the Alaska Peninsula this evening, and into the
Gulf late tonight. A short wave rounding the southern side of the
High Arctic upper low will move through the Siberian Arctic Coast
today, to cross the Chukchi Sea tonight to move over the western
AK Arctic Coast Monday morning. A second piece of energy will move
out of the Chukotsk Peninsua Monday night to the western Seward
Peninsula Tuesday morning. These two features will effectively
work to form an upper trough over the western third of the state
by Tuesday, while squashing the upper ridging over the Bering
Sea. Additional short waves dropping down the backside of this
newly formed trough from eastern Siberia, combined with the upper
low south of the Kamchatka Peninsula moving east across the
Aleutian Chain toward Bristol Bay, will further act to deepen this
trough Wednesday. Upper level ridging becomes restablished over
the western Bering and east Siberia Wednesday night.

North Slope/Brooks Range: A weak disturbance will move north into
the eastern Brooks Range tonight, bringing a round of rain to this
region as well as the eastern Arctic Coast. Snow levels will
remain high around 5000 feet. Easterly flow will continue over the
central and eastern Arctic Coast with a 1016 mb area of high
pressure over the eastern Beaufort Sea, which will drift off to
the northeast north of Banks Island by Tuesday. This will promote
periods of fog and stratus to persist through tonight, before
winds just off the deck turn more offshore for Monday. A weak
surface low will pass just south of Wrangel island this afternoon
and move out into the Chukchi Sea tonight, then slowly drift to be
located near Cape Lisburne by late Monday night. A weather front
will extend in front and to the south of this low, which will
bring another round of rain to the western Arctic Coast and
western Brooks Range late tonight into Monday. The front will
continue to advance east through the eastern half of the North
Slope and Brooks Range, to bring rain to this region by Tuesday
afternoon. Showers will wrap around the low circulation over the
western Arctic Coast and western Brooks Range on Tuesday, with
snow levels falling to around 2500 feet, and down to around 3000
to 3500 feet on Wednesday for the central Brooks Range.

West Coast/West Interior: Ridge of high pressure will weaken over
the West Coast tonight, as a weak surface low will pass just
south of Wrangel island this afternoon and move out into the
Chukchi Sea tonight, then slowly drift to be located near Cape
Lisburne by late Monday night. A weather front will extend in
front and to the south of this low, which will bring another round
of rain to the Chukchi Sea Coast and western Seward Peninsula late
tonight into Monday, pushing through the western Interior Monday
night into Tuesday. Lighter rain/showers are expected south of
the Seward Peninsula. Showers will wrap around the low circulation
over the Chuckchi Sea Coast and western Brooks Range on Tuesday.
Southerly winds to around 25 knots will accompany the frontal
system through the Bering and Chukchi Sea tonight into Monday
morning, followed by gusty northwest winds to around 30 knots that
will develop on the backside of the low pressure system Monday
evening into Tuesday. The strength of the wind and fetch looks
favorable enough for high surf and potential beach erosion for
Shishmaref developing Monday night and continuing through
Tuesday, before winds turn to the north and diminish Tuesday
night.

Central and East Interior: Scattered showers are expected for
Interior Alaska through Monday, with the best chances focused
along the Alaska Range. These showers will be diurnally enhanced,
and isolated afternoon/evening thunderstorms will be possible for
the east Interior through this evening. A weak disturbance will
move north from the east Interior, which will continue to bring rain
to the southeast Brooks Range, mainly from the Dalton Highway east
tonight. Rainfall amounts look to be lighter compared to
yesterday, generally up to one half inch or less with the heaviest
amounts around Arctic Village. A weakening weather front moves
into the central Interior Tuesday, helping to refocus an area of
light rain or showers here, to push into the east Interior by
Tuesday night.


Coastal Hazard Potential Days 3 and 4...Low pressure will move
from Cape Lisburne Tuesday to the eastern Beaufort Sea on
Wednesday. Northerly winds on the backside of this low could
produce high surf over the central Arctic Coast by Thursday.

&&

.FIRE WEATHER...No concerns at this time. Slight chance of
thunderstorms this afternoon and evening from Fairbanks north and
east. Chance of wetting rain remains relatively high in the upper
Yukon Flats and eastern Brooks Range. Some drying for the western
Interior on Monday, but Relative Humidity values remain high and
will generally be above 40 percent. Sustained winds less than 15
mph.


&&

.HYDROLOGY...Flood Advisory continues for the Tetlin Road, for
the latest information go to www.weather.gov/fairbanks.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...

Flood Advisory for AKZ224.

Small Craft Advisory for PKZ210-PKZ220-PKZ225-PKZ230-PKZ245.

&&

$$

NTS AUG 17


000
FXAK68 PAFC 210103
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
503 PM AKDT Sun Aug 20 2017

.ANALYSIS AND UPPER LEVELS...
Another cold upper level trough that originated over the Arctic is
currently located over the Interior and digging toward the Southwest
mainland of the state. A fairly strong ridge over the central
Bering Sea is pushing into the trough causing gusty north to
northwest winds over the eastern Bering Sea and Southwest Alaska.
The surface low is in the Gulf of Alaska and is strong enough to
bring northerly winds to much of Southcentral Alaska as well.
One interesting note with the pattern over Southcentral is that,
if it was wintertime, it is a pattern that would bring in a lot
of snow to the main population centers of Southcentral Alaska. All
the precipitation will be rain with this system, but the overall
pattern would be a snowy one if it was winter.

&&

.MODEL DISCUSSION...
Models remain in good agreement both in regards to one-another
and with run-to-run consistency. All show this latest Arctic
trough dropping out of the interior of the state, through the
Bristol Bay region overnight and into the Gulf of Alaska for
Monday and Tuesday. By Wednesday models are also all indicating
moist southwest flow returning to Southwest and Southcentral
Alaska and therefore more rain. Confidence is increasing for this
mid-week pattern to develop.

&&

.AVIATION...
PANC...Rain will persist but the low level flow is from the north
instead of the southwest with this system which is different from
most of the recent rainfalls. What is pertinent about this is
ceiling heights generally are higher with northerly flow than
southwest flow.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Tonight
through Wednesday)...

Widespread steady rain will persist across most of Southcentral
Alaska tonight as a surface low tracks northward across the Gulf
out ahead of a strong upper level trough/low dropping south across
Southwest Alaska and into the southwest Gulf. The upper level low
will track south of Kodiak Island late tonight then continue
east-southeast across the southern Gulf on Monday. The surface low
will be pulled southward toward the upper low leading to a
gradual tapering off of rain over Southcentral on Monday,
lingering longest along the Gulf coast. The northern half of the
Copper River Basin, from Glennallen northward, will remain on the
northern periphery of the rain shield, so expect little or no rain
from this system.

Aside from the rain, also expect robust winds with this storm
system. Expect widespread Small Craft to Gale Force winds across
the Gulf coastal waters tonight through Monday. The strongest
winds will be along the south side of the Alaska Peninsula,
including Shelikof Strait. The passage of the upper low and
accompanying jet streak will combine with tightening low level
pressure gradients to really accelerate winds through bays and
passes.

Look for a warmer, drier day across Southcentral on Tuesday as the
Gulf storm exits and weak ridging slides in from the west. Expect
increasing sunshine from the western Gulf to Cook Inlet (including
Anchorage and the Matanuska Valley) with favorable north to west
flow. It looks like clouds may hold in farther north and east on
the periphery of the exiting low and a trough crossing interior
Alaska.

There is high confidence in another widespread rain event beginning
Wednesday afternoon as a broad trough moves in from the Bering
Sea, setting up deep southwest flow. The rain will likely linger
through late in the week.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A highly amplified pattern is on tap with an upper low over
southwest AK and the ridge axis to the west. The models continue
to drop this low south-southeastward. In the wake of the low
passage, high pressure will build in and expect a tight pressure
gradient from Bristol Bay to the AK Pen where gusty winds are
anticipated. Additionally, as the ridge moves inland expect the
skies to become partly cloudy and clear in several locations on
Monday. Tuesday will be mild and pleasant.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
High pressure will continue to build over the Bering Sea,
resulting in widespread stable conditions over much of the area.
The caveat being the eastern Bering/Aleutians and Alaska
Peninsula...where a tight pressure gradient will set up.
Anticipating gap winds south of the Alaska Peninsula to ramp up
tonight and reaching Gale force by tomorrow morning. As time
elapses a new low will approach the archipelago from the
southwest bringing rain to the western Aleutians.

&&

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

Beginning the extended period forecast Wednesday night, there will
be a deepening upper level trough over the state of Alaska with a
subtropical warm front at the base of this trough over the North
Pacific. Some of this moisture will be moving north toward the
Gulf, so this system will have some enhanced moisture aiding it.
Rather widespread rain in southwesterly flow aloft will be
impacting most of Southern Alaska through Thursday night. However,
by Friday, the main upper low and associated trough position will
dig into the Gulf of Alaska, so the steadiest rainfall will begin
to shift towards the coastal areas and Bristol Bay while more
showery conditions (instead of steady rain) develop over interior
locations. All the global numerical models depict a similar fate
to the upper trough as it weakens in place over the North Gulf
Coast through the weekend, likely keeping some clouds and shower
threats through the weekend.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales...119 120 130 131 139 150.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS
LONG TERM...JA


000
FXAK67 PAJK 202305
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
305 PM AKDT Sun Aug 20 2017

.SYNOPSIS...An atmospheric river with abundant moisture from the
remnants of dissipated typhoon Banyan will advect moisture across
the western Gulf and panhandle with periods of rain occurring
through Monday.

&&

.SHORT TERM...Through Tuesday morning...Showers will continue
moving across the panhandle this evening. An atmospheric river
will advect abundant moisture across the panhandle the next few
days advecting moisture from the remnants of dissipated typhoon
Banyan across the region. Rain will continue with periods of
heavy rain occurring at times primarily across the souther areas
of the panhandle. Temperatures will remain cool with cloudy skies
and rain continuing across the panhandle. Winds will remain light
to moderate across inland areas.

Only minor changes have been made to the forecast. The NAM, GFS,
and ECMWF are in good agreement for the forecast the next few
days.

.LONG TERM.../Tuesday through Sunday as of 10 pm Saturday/ The
extended forecast remains cool, wet, and fall-like. Tuesday begins
with a weather front moving across the Panhandle. Periods of heavy
rain are expected on Tuesday within the southern Panhandle due to
enhanced moisture directed at the area from the remnants of
Tropical Storm Banyan. Models slowed the progression of the
heaviest band of precipitation slightly from yesterday, with total
rainfall between 0.5 to 1.5 inches forecasted Tuesday. Greatest
values are expected near Ketchikan and Annette Island. The outer
coast and far northern Panhandle will have much lower rainfall
totals with possible breaks in precipitation as the front pushes
to the southeast Tuesday.

Wednesday and Thursday will likely be characterized by remnant
scattered shower activity over the Panhandle with a break in
preciptiation likely sometime Thursday. Late Thursday night
another weather front will begin to move across the Panhandle
bringing a return to rain. This front will keep conditions wet
once again next weekend. The front`s exact arrival time is still
an area of uncertainty, but between late Thursday night and Friday
morning is currently the most probable.

Not many significant changes were made to the extended forecast.
Tuesday`s QPF values were increased due to being in agreement with
a slowing of the heaviest band of precipitation. Tuesday`s
forecast was nudged toward the 00z NAM with WPC input being used
for Wednesday and beyond as needed.

&&

.AVIATION...Marginal flight conditions due to Ceiling forecast
for the late afternoon and into the evening. Rain spreading to the
panhandle with System associated with the former Typhoon Banyan.
A low level jet near the coast will lead to low level turbulence
overnight for the coast and then will move to the inner channels
toward morning as it move to the Clarence and then Stephens.

&&

.MARINE...An early season gale will develop in marine zone 52 as
the second front approaches the central gulf coast tonight.
Elsewhere small craft seas to 8 feet and winds of 25 to 30 kt
will impact the outside waters for much of the next twenty- four
hours.

&&

.HYDROLOGY...Moisture from Banyan`s remnants (up to 3 plus
standard deviations above atmospheric normals of IVT) will begin
to spread across all sections of the Panhandle overnight. But the
most concentrated area of heavy rains continues to be forecasted
for the southern Panhandle, tonight into early Tuesday. Looking
for a minor break in the rainfall afternoon to early evening over
the southern with light rain totals. We expect significant rises
in streams beginning tonight and continuing into Tuesday. Special
weather statements cover heavy rain and significant rises on
rivers, streams, and lakes. Flooding is not expected, but we will
continue to evaluate threats through the event.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Gale Warning for PKZ052.
Small Craft Advisory for PKZ022-036-041>043-051.

&&

$$

BM/JWA

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