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000
FXAK69 PAFG 191633
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
733 AM AKST Mon Feb 19 2018

.SYNOPSIS...
Aloft...
A high amplitude long wave ridge over Alaska and trough over the
Bering and NW Pacific will become more zonal through the week as
a series of very strong short wave troughs move NE across the
bering Sea and Alaska the next several days. This will keep
northern Alaska in a warm, wet and windy pattern the next several
days.

Surface...
A 990 mb low west of Wrangel Island will drift northwest. A front
from this low to Prudhoe Bay to Northway will move to the Alcan
Border by 3pm today. Light snow with this feature will end west of
the front.

A 960 mb low in the central Bering Sea will move to Cape Navarin
as a 964 mb low by 3pm mon, to 200 nm northwest of Cape Lisburne
as a 988 mb low by 3pm Tue, and to 300 nm northwest of Barrow as a
999 mb low by 3pm Wed. The front with this low will move along the
West Coast today, to Barrow to mcGrath by 3am Tue, and to the
Alcan Border by 3am Tue. Expect 4-8 inches of snow with this along
the west Coast and Western Interior today, and 1-2 inches with it
over the Eastern Interior Tue. SE Gales ahead of the front are
causing blizzards along the Coast today through Tue.
The poison tale following the low center will move over the West
Coast tonight causing south winds gusting 50-90 mph with the
highest winds over the Western Capes.

A third low will move north into the southern Bering Sea Tue
night and to the central Bering Sea on Wed.


.DISCUSSION...
Models initialize well aloft. At the surface the low just NW of
Wrangel Island is about 4 mb deeper than models at 06Z, and the
surface high over the Copper River Basin is about 4 mb stronger.
Main low in the central Bering appears to be well initialized at
06z. Will see bit stronger winds through Alaska Range passes
today than models shows as a result of the high pressure being
stronger than models indicate.

Models generally in agreement through 3am Wed, then the GFS moves
the next Bering Sea low northeast faster than the ECMF and NAM.
At this point favor the slower NAM/ECMF solutions for Wed. Models
diverge on strength and timing of short waves after Wed, but one
certainty is that the progressive westerly flow pattern will
continue through the week.

&&

.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-AKZ227.

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

Brisk Wind Advisory for PKZ230.
&&

$$

FEB 18


000
FXAK68 PAFC 191351
AFDAFC

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

.ANALYSIS AND UPPER LEVELS...
A high amplitude ridge has reasserted itself over the Alaska
mainland this morning as the remnants of a weak trough that
brought light snow to southcentral yesterday rapidly moves east
towards the ALCAN border. Skies are clearing rapidly behind the
front over southcentral though a stubborn stratus deck has
remained over the Cook Inlet/Knik Arm area with low clouds
covering the Anchorage Bowl and the Matanuska Valley. A strong
southerly jet over the Central Bering is supporting a storm force
surface low currently centered near the Gulf of Anadyr with a
front extending far out ahead of it moving east across the Eastern
Aleutians. This front is bringing warm moist air, with
temperatures climbing into the 40`s, as well as strong winds to
the Aleutians/Bering.

&&

.MODEL DISCUSSION...
Models are in good agreement this morning showing a persistent
ridge building in over the eastern half of the state with a front moving
across the Bering and into SW Alaska Monday night before being
sheared apart as it runs into the ridge, keeping Southcentral
mostly dry. Models begin to differ some on Thursday as a
subsequent, more potent system comes barreling across the state.
The GFS/NAM are a bit quicker than the EC/Canadian solutions, but
all agree that this system will break the ridge down some allowing
snow to make its way into southcentral by at least Thursday
night.

&&

.AVIATION...
PANC...Stratus has stuck around the Anchorage Bowl this morning
with predominate MVFR conditions expected with some intermittent
lower IFR Cigs building in, as seen in nearby METARS. An upper
level ridge axis will move over Anchorage today which should help
to scatter out the low clouds this afternoon, at least directly
over the terminal. The ridge axis though, with strong subsidence,
clearing skies, and weak flow, will again favor the development of
low stratus and fog tonight and into tomorrow morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
High pressure will build over Southcentral Alaska today. Some
stratus remains over the Cook inlet area this morning, which
should break up this afternoon. This ridge will remain over the
area through Tuesday night. A weak upper level trough will briefly
lower heights with the ridge as it traverses the area on Tuesday.
Although this system is fairly dry, some precipitation is possible
in the morning from about Anchorage northward, as well as over
the Copper River basin from late morning into the early afternoon.
This will also weaken the low level offshore gradient. Upper
level heights then increase as the the ridge rebounds Tuesday and
Tuesday night.

&&

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

A powerful storm force low over the western Bering Sea is
supporting a strong cold front over the eastern Bering Sea--this
front is currently tracking toward the coast. Strong southerly
winds ahead of this front are already gusting into the 40-45 MPH
range and will remain strong through early morning. The front
will then move inland through tonight, bringing rain and snow to
all of Southwest Alaska, although any accumulations will be minor
as the front will quickly weaken as it moves inland. High pressure
settles in for Tuesday before a warm moves into the Kuskokwim
Delta, bringing another shot of rain/snow as the progressive wave
pattern continues.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

A strong 959 mb low is currently taking shape over the Bering Sea
this morning. Early morning scatterometer satellite passes have
captured near storm force winds over the far southwest Bering Sea,
and this low is expected to strengthen to storm force today as
cold air advection wraps around the surface low. Sea states are
still expected to reach near 40 ft over the northwestern Bering
Sea as the low tracks northward. The gale force front will clear
the Eastern Aleutians by tonight with brief high pressure settling
over the Bering. The next weaker gale force low will move into the
Bering Tuesday and will lift north through Wednesday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The general trend for the long term forecast beginning the middle
of this week will be for continued active weather moving from the
Bering through the Mainland into next weekend. This will be
produced by a flattening the ridge that has setup over the North
Pacific, allowing for a broad westerly jet to stretch from the
Aleutians through the Mainland and into British Columbia. This
pattern will bring a series of Bering systems to begin impacting
the South Mainland with chances for rain and snow, the first looks
to move through late Wednesday into Thursday. After this system
passes through model agreement begins to decrease significantly
with the track of the upper level low over the Western Bering and
how it interacts with the the North Pacific ridge. As a result the
forecast uses ensemble guidance heavily starting Friday, leading
to a broad brushed and generally low confidence forecast for most
of the area through next weekend.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm Warning 185.
Gale Warning 165 170 173 174 175 176 177 178 179 180 181.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...KVP
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...DEK/SEB


000
FXAK67 PAJK 191343
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
443 AM AKST Mon Feb 19 2018

.SHORT TERM.../Monday through Tuesday night/...Two fast moving
features are the focus of the short term. Currently, a weak low
pressure system is creating snow showers along the gulf coast.
Shower activity is mainly along Baranof and Chichagof Island
currently; however, as the low tracks southeast some showers will
likely affect Prince of Wales Island as well. Up to 1 inch of snow
is possible associated with the snow showers. The system is fast
moving so shower activity will not be long lived. Skies will clear
behind the low.

Tomorrow will skies will gradually cloud up as a weak short wave
trough aloft descends southward over the Panhandle. At the
surface, most of the energy looks to remain over Canada which
will keep any showers that do happen to form over the Panhandle
relatively isolated.

Temperatures continue to be slightly cooler than average. Daytime
highs will range from the low to high 30s. Overnight lows will
range from the low 20s to the low 30s. This continues the drier
and colder than normal February thus far.

The most significant adjustment made to the short term forecast
was to speed up the low currently over the eastern gulf and
increase shower activity along the outer coast this morning.
Primary guidance was the 00Z GFS with some input from the 06Z
NAMNest for winds. PoP and QPF from the Canadian NH, NAM NMM, and
NAM DNG. Forecast confidence is above average.

.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 the Alaskan
interior 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. The Sunday 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 latest GFS (at the time of this writing) 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.

&&

$$

JB/SS

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