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000
FXAK69 PAFG 200053
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
353 PM AKST Mon Feb 19 2018

.DISCUSSION...
An active weather pattern is expected to continue for much of
northern Alaska for the next few days. The immediate concern is a
strong weather front that will bring very strong winds (in some
cases gusts up to 90 mph) to St. Lawrence Island, the Bering
Strait coast tonight and to portions of the Chukchi Sea coast
early Tuesday. This front will also bring precipitation as it
moves from west to east across the forecast area tonight into
tomorrow. Another round of precipitation will move across northern
Alaska Wednesday night into Thursday. The models are in very good
agreement out through the end of the workweek.

West Coast and Western Interior: A strong low is currently moving
to the north up the east coast of Russia. A front associated with
this low will continue to push through the west coast this evening
and will push through the western Interior tonight. Cold air
wrapping around the low will bring very strong winds to areas
immediately southeast of the low tonight into early tomorrow.
This will cause wind gusts up to 90 mph from the southwest tonight
on St. Lawrence Island and along the coast of the Bering Strait
with gusts up to 90 mph expected from Kivalina north to Point Hope
early tomorrow moving. For areas south the the Bering Strait
freezing rain may mix with snow at times. The heaviest snowfall
with this system will be in the upslope region just south of the
Brooks Range in zones 208 and 217. The strong southwesterly winds
may push some sea ice onto beaches along southwest facing coasts
and may cause some minor coastal flooding. On St Lawrence Island
(especially Gambell), there is better potential for water to be
pushed ashore due to lower sea ice concentrations south of the
island. A Coastal Flood Warning is out for zone 213 for tonight
and Tuesday with coastal flood advisories out for much of the
remaining coastline along the west coast. Winds will gradually
decrease tomorrow and tomorrow night. The next round of
precipitation will begin to push into the west coast during the
day on Wednesday and will push into the western Interior Wednesday
night. Areas south of the Bering Strait may see freezing rain mix
with the snow at times with this round as well.

Central and Eastern Interior: A weather front will push through
the Interior tonight into early Tuesday. This will bring 1 to 2
inches of snowfall to the Interior as it moves through. This
front will also bring some gusty winds, particularly northeast of
Fairbanks along the Steese Highway. A potentially more
significant snowfall event is expected Wednesday evening into
Thursday. Current guidance also has westerly winds kicking up as
the front goes through. Some of the current guidance is suggesting
that Fairbanks could see 5 to 7 inches of snowfall from Wednesday
evening into early Friday morning. The GFS is also suggesting
wind gusts in the Fairbanks area Thursday evening in excess of 30
mph. The NAM and the ECMWF are not as strong; however they are
still showing winds in the 15 mph range.

North Slope and Brooks Range: Expect winds to increase this
evening as the low moves to the and the front moves to the east.
As the winds pick up blowing snow will increase in intensity.
Areas to the west of Point Lay may see gusts up to 90 mph at times
early Tuesday. Strong winds will taper off from west to east
Tuesday night. Snowfall amounts north of the Brooks Range through
tomorrow afternoon will generally be in the 2 to 4 inch range;
however in the Brooks Range there will be locally heavier amounts.

Coastal Hazard Potential Days 3 and 4...None.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
Coastal Flood Warning for AKZ213.

Coastal Flood Advisory for AKZ207-AKZ209-AKZ210-AKZ211-AKZ212-
AKZ214.

Winter Storm Warning for AKZ201-AKZ208-AKZ210-AKZ211-AKZ217.

Blizzard Warning for AKZ207-AKZ209-AKZ213.

Winter Weather Advisory for AKZ202-AKZ203-AKZ204-AKZ206-AKZ212-
AKZ214-AKZ215-AKZ216-AKZ218-AKZ220.

Gale Warning for PKZ200-PKZ210-PKZ215-PKZ220-PKZ225-PKZ230.

Brisk Wind Advisory for PKZ235-PKZ240-PKZ245.
&&

$$

FEB 18


000
FXAK68 PAFC 200119
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
419 PM AKST Mon Feb 19 2018

.ANALYSIS AND UPPER LEVELS...
A ridge of high pressure moving over the Mainland is providing
enough subsidence to bring widespread stratus with some fog mixed
into much of the southern Mainland and Gulf of Alaska today. The
worst conditions have occurred around Kodiak Island where periods
of dense fog occurred earlier this morning, but this is beginning
to diminish as westerly flow develops as well as the daytime
heating. Over the eastern edge of the ridge axis, a strong
northerly jet is bringing widespread upper level cloud cover
stretching from Southcentral into the Gulf, which is slowly moving
to the east in advance of an incoming front over the Eastern
Bering. Over the Kuskokwim Delta coast the first signs this gale
force front is beginning to appear with rain/snow showers along
with strong southerly winds. This is the same front that brought
rain and widespread storm force winds along with a brief round of
high winds to the Aleutians yesterday. It has now weakened some
as it detaches from the upper level low centered well to the west
near the Siberian Coast.

&&

.MODEL DISCUSSION...
As has been the case over the past few days, the models remain in
very good synoptic agreement into mid week, leading to generally
good forecast confidence throughout the area. The biggest forecast
concern in the short term forecast surrounds the potential for
snowfall from the weak shortwave that will ride along the
flattening ridge over the North Pacific late for Tuesday morning.
At this point the highest confidence for accumulating snow is
over the Northern Susitna Valley and Copper River basin where
there is good model consensus of another quick shot of light
snowfall. More uncertainty exists along the southern edge of this
shortwave over Anchorage and the Matanuska Valley where the
models bring little (if any) snowfall, leading to much lower
forecast confidence in the potential for snowfall here.

&&

.AVIATION...
PANC...After a brief break in the LIFR stratus and patchy fog this
afternoon and evening, continued subsidence from high pressure
moving over the area will likely allow for its redevelopment
by late this evening. The one piece of good news is that these
LIFR conditions will likely diminish much quicker (around 15z)
than had been the case over the past few days as some mixing from
a shortwave approaching from the west pushes through. There is an
outside chance that this shortwave could bring a brief light snow
shower, but at this point it appears that the biggest impact from
it will be to keep ceilings hovering around 5000 ft for Tuesday
morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Fairly benign conditions will prevail cross much of Southcentral
through tonight beneath the ridge, keeping patchy fog across the
Cook Inlet region and widespread low stratus over the Copper
River Basin during the overnight hours. A weak shortwave will then
briefly flatten out the ridge as it traverses the northern half
of the area Tuesday morning. This will likely bring a dusting of
snow to portions of the Susitna Valley from about Talkeetna north,
with snow then spreading into the northern Copper River Basin
through early Tuesday afternoon. Areas farther south including
Anchorage and the Matanuska Valley may see a brief snow shower
towards daybreak, but the threat of precipitation will quickly
come to an end as the shortwave exits to the east. This will usher
in another period of quiet weather through Wednesday as ridging
is quickly re-established over the mainland, with the familiar
potential for patchy fog and stratus returning to the area by
Tuesday night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
(Tonight through Thursday evening)

An active pattern looks to continue for the next few days, as a
strong cold front is currently moving shore. Widespread rain and
snow showers have developed ahead of this feature, with winds
gusting over 40 mph along the majority of the coastal locations.
This front will continue its eastward trek through the night,
reaching the Alaska Range by morning. Colder air advecting back
across the mainland will quickly change any mixed precipitation
back to all snow later tonight. However, only minor accumulations
are anticipated.

Otherwise, look for a transient ridge of high pressure to build
across the region once again for Tuesday afternoon, before another
warm front brings precipitation back to the area late Tuesday
night, followed by a cold front for Wednesday, with more rain and
snow showers. Although the cold front looks to clear the area on
Thursday, a trough axis extending south from a low near the Seward
Peninsula will keep showery-type precipitation lingering across
the region through the evening.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
(Tonight through Thursday evening)

A gale force front currently extends from the far eastern Bering
through the AKPEN, with widespread rain and snow showers
accompanying it. This low is attached to a 965 mb low over the
Chukchi Sea, with storm force winds observed over the northwest
Bering on the latest scatterometer pass. Here, seas of 35 to 40
feet and sustained winds of 55 knots or more can be expected.
Higher wind gusts are also likely given the very cellular
signature seen in satellite imagery.

Further south, a ridge of high pressure will develop from the
east central Aleutians through the central portions of the sea
over the next 18 to 24 hours, bringing a brief period of drier
weather with decreasing winds. This will be short-lived however,
as one storm enters the southwest Bering Tuesday evening, sending
a cold front eastward through the Aleutian chain/Bering on
Wednesday as the parent low lifts northeast. Yet another storm is
waiting in the wings for Thursday evening.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The pattern in the long term looks to be an active one with
multiple systems moving through the area over the next week. The
main low centers look to track through the Bering with the fronts
still making it over the southern mainland. However, with the
associated low centers further away, the fronts do not look to be
very strong by the time they make it to the southern mainland.
There is decent confidence amongst the models on the overall
pattern but they are struggling with exact placement of the main
lows. Further out in time, ensemble means were preferred over the
deterministic solutions.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 174-178 181.
Storm 185.

&&
$$

SYNOPSIS AND MODEL DISCUSSION...DEK
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...DK


384
FXAK67 PAJK 192331
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
231 PM AKST Mon Feb 19 2018

.SHORT TERM...Weather pattern in the short term will continue to
be dominated by amplified mid/upper ridging over the western Gulf
and interior of AK. Weak shortwave energy that brought 1 to 2
inches of snowfall to the central and southern coastal areas this
morning is currently continuing to push south towards the Pacific
NW of the US mainland this afternoon. As this trough amplifies
slightly, weak cold advection will set up tonight, and northerly
winds will respond accordingly. Not expecting any real marine
hazards with only 20 kt northerly flow in Lynn Canal.

A piece of mid level energy will break off from the strong system
over the Bering Sea and attempt to make a run over the mean ridge
by late Tuesday. This system will be moisture starved and rather
weak, tracking a bit further east than the system from this
morning. Some light snowfall is possible for a few hours over the
northern and interior Panhandle by Tuesday evening as this system
tracks overhead, with minimal if any accumulation expected.

Ridge will begin to flatten late on Wednesday night as a stronger
upper shortwave approaches from the Bering. Height falls over the
northern Gulf in response to the approaching upper trough will
induce a weak surface trough by late Wednesday night.
Additionally, strong W`ly flow aloft will allow surface pressures
to fall over the Yukon. This will set up a tightening southerly
surface pressure gradient by late Wednesday night with the
majority of the southerly push felt initially in the northern
Panhandle. Adjusted temps up on Wednesday night over the north
based on expected increasing cloud cover and increasing southerly
winds which may eventually have some bearing on precip type
concerns for Thursday. Still some model timing and strength
differences regarding this system so left Thursday alone for now.

Overall, good agreement with a low impact forecast through
Wednesday.

.LONG TERM... / Wednesday through Sunday as of 9 PM Sunday/ A
ridge of high pressure continues to remain in place over the Gulf.
A shortwave and its associated surface low will reach Alaska`s
mainland by early Thursday, pushing southeast over the panhandle
and dying by late Thursday night. The ridge looks to flatten later
this week and bring in another system Saturday and another
potential shortwave into the day 7/day 8 timeframe.

Changes to pressure were mostly the result of a GFS/ECMWF blend
early on and continuing with some WPC after Friday. Today`s WPC
discussion mentions not using the GFS in their own blend due to a
much faster track for Thursday`s system than previous model runs.
However, the GFS seems to line up quite nicely with the ECMWF for
the mid-week time range. Despite a tightening pressure gradient
over the northern panhandle, wind speeds were decreased locally
based on MOS Guidance. And as Thursday`s system ramps up, winds
over the Gulf were increased and will easily reach 35 kt.

Temperatures will be on an increasing trend, before dropping
steadily after Friday. To go along with this trend, the NBM was a
nice middle ground and matching well with both WPC and MOS
Guidance. Thus, maximum and minimum temperatures were raised
accordingly through mid-week.

The NAM/SREF was used early on for changes to POP, which
decreased POP`s for Wednesday`s system and confining any
precipitation/ flurries to the early morning hours. POP`s were
increased for Thursday with precip beginning in the late afternoon
and QPF increased slightly using a blend of the GFS/RFC. Snow
levels were once again raised, but with preliminary snow amounts
of up to 2-3" across the panhandle for Thursday.

Although confidence is still not great through the latter portion
of the period, we have seen a slight improvement compared to
yesterday.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...None.

&&

$$

DEL/SS

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