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000
FXAK69 PAFG 222340
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
240 PM AKST Wed Nov 22 2017

.DISCUSSION...

Aloft...at 500 hpa...A 504 dam low northwest of Point Barrow will
move across the northern interior and persist into the weekend. A
505 dam low over Bristol bay will drop to the south tonight and
move into the Gulf of Alaska on Thursday. Ridging will build back
over the Bering sea and west coast on Friday.

Surface...980 mb low over the Chukchi sea will track near
Barrow and weaken to 991 mb by Thursday evening. A strong
968 mb low near Nunivak island will quickly track south across
the Aleutians Thursday morning. Another low pressure system will
move into the Western Bering on Saturday.

Arctic Coast and Brooks Range...Blizzard to near Blizzard
conditions continue over the Western Brooks Range and Northwest
Arctic Coast. Winds will slowly diminish through the evening. The
low will track near barrow by Thursday afternoon and continue
to weaken and then track across the Brooks range. Snow showers
will persist for the north slope around the low center through
friday.

West Coast and Western Interior...Blizzard conditions primarily
north of the Seward Peninsula this morning will diminish through
the day. However, a rapidly moving low in the Bering Sea will move
to Nunivak Island this evening spreading Blizzard conditions to
the lower Yukon Delta by this afternoon as winds ramp up with
gusts to 70 mph along the coast. The remainder of the Delta will
have winds gusting to around 45 mph. Heavy snowfall can be
expected in the lower Yukon Delta as well with 6 to 12 inches of
snow.

Central and Eastern Interior...Snow will taper off to
flurries across the Tanana valley as the shortwave moves east
this evening. Cloudy and cold through through the remainder
of the week.

Coastal Hazard Potential Days 3 and 4...Have cancelled the last
of the coastal flood products. Winds and waves will continue to
diminish through this evening. Models still bringing a storm to
the Bering Strait Saturday that has the potential to produce high
surf along the southern Seward Peninsula, and the Chukchi Sea
Coast north of Cape Espenberg.

Extended Forecast days 4 to 7...Better agreement in the guidance
for the mid and extended periods with the latest solutions. Expect
high pressure building over the Arctic, and Central and Eastern
Interior with cooling temperatures. Lows on the weekend falling
into the 20s below or colder, then warming a bit to start the
week. No new snow expected in the interior through the middle of
next week.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning for AKZ212.

Blizzard Warning for AKZ201-AKZ205-AKZ213-AKZ214-AKZ215.

Heavy Freezing Spray Warning for PKZ200-PKZ220-PKZ225-PKZ230-
PKZ235.

Gale Warning for PKZ210-PKZ230-PKZ235.

Small Craft Advisory for PKZ200-PKZ220-PKZ225.
&&

$$

JK NOV 17


000
FXAK68 PAFC 230128
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
428 PM AKST Wed Nov 22 2017

.ANALYSIS AND UPPER LEVELS...
The frontal system over the Bering is beginning to spread snowfall
along with gusty southeasterly winds into the Kuskokwim Delta and
Western Bristol Bay. This front is part of a much larger system
that is taking up most of the Bering Sea, with a good supply of
cold/dry air advecting into the low allowing for continued
intensification as it moves onshore. This surge of cold/dry air
also helping to bring gale force winds throughout the Central
Bering, which are expected to increase to widespread storm force
as it moves into the Eastern Bering/Aleutians. Over the Gulf and
Southcentral, conditions are much quieter than the Bering with a
brief break from the active weather in a continued progressive
pattern. This will begin to break down late tonight as the frontal
moving through the Southwest Mainland produces a triple point low
in the gulf.

&&

.MODEL DISCUSSION...
The models remain in very good synoptic agreement in the early
term before starting to break down early Thursday with the
positioning and intensity of the triple point low in the Western
Gulf. In particular, the GFS continues to be both the deepest and
furthest west with that low, and was generally ignored today in
favor of the further east/weaker solutions of the NAM and EC.
These differences then become larger on Friday with large
differences in how quick the low will depart the southern Gulf, the
NAM being the slowest. The speed that this low departs the Gulf
will weigh heavily in how strong winds over the North Gulf Coast
and will need to be monitored as trends towards the NAM position
will produce stronger winds than currently forecast.

&&

.AVIATION...
PANC...VFR conditions with light winds will continue today, before
ceilings near 5000 ft move into the area beginning late tonight.
There may also be a few flakes as ceilings drop on Thursday
morning, however these are expected be very light with VFR
conditions expected.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 2)...

Dry weather prevails across the southern mainland through Friday
evening as an offshore pattern persists. Active weather across the
Southwest mainland brings a front across to the western gulf
tonight spreading precipitation across much of the gulf including
the Kenai and Kodiak Island through Thursday morning. The front
weakens as it slides across the central waters Friday afternoon
then remains stationary and diminishes heading into Saturday
morning.

The main concern surrounds offshore winds for typical gusty areas
through channeled terrain. As the surface low moves into the gulf
late Thursday night a ridge shifts from the Yukon Territory to
the central interior. The ridge forces a cold dense air mass
toward the coast which actively increases winds overnight Thursday
through Friday.

&&

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

Gusty winds and widespread snow associated with the Bering storm
will continue to impact portions of southwest Alaska. At times,
the models ping into moderate to heavy snowfall. Periods of
blowing snow and white out conditions are also possible tonight
and tomorrow morning. The frontal boundary will move inland and
stall near Bethel, then slowly decay. Cold and drier air will be
steered into the region Thursday night. Isolated showers will
linger over the region through the end of the period but
significant accumulations not expected after Thursday.

&&

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

The forecast period commences with an unsettled pattern in place,
complete with wintry precipitation, strong winds and rough seas.
The latest scatterometer pass has the Bering front east of the
Pribilof Islands this afternoon. Behind the low center, widespread
northwest flow and strong cold air advection. A tight pressure
gradient will continue to bring strong winds to much of the
Bering and the Central/Eastern Aleutians. The winds will gradually
diminish for all areas from west to east for the Bering and the
Aleutian archipelago by Friday morning. Looking upstream, a dome
of high pressure will build into the Western Aleutians early
Thursday with the ridge axis east of Atka by Friday morning.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long term portion of the forecast begins Friday night with a
familiar outflow wind pattern in place across much of southern
Alaska, with a ridge over the Bering Sea and a longwave trough
extending along the Alcan border into the eastern Gulf. This will
keep most of the area cold and dry well into the weekend before
the ridge breaks down and the pattern begins to shift once again
Sunday into early next week.

Forecast confidence quickly diminishes by the beginning of next
week as a deep trough over eastern Russia sends a series of
shortwaves into the Bering Sea. Models continue to show poor
agreement with respect to the evolution of these waves and
subsequent development and placement of surface features. It
appears that a deep low will rapidly intensify over the Bering
Saturday night and then move to the general vicinity of the Alaska
Peninsula by late Sunday, sending a front near the southwest
coast and bringing the threat for another round of mixed
precipitation and gusty winds to portions of Southwest AK. An even
deeper low then looks to approach the Aleutian chain on Monday,
bringing stormy conditions to the southern Bering with the details
largely dependent upon the track of the low through the middle of
the week. Guidance is also hinting at another system moving into
the western Gulf in the Monday/Tuesday time frame, but confidence
is low at this time as specific solutions remain all over the map.
Generally speaking, those in southern Alaska can expect chances
for precipitation to increase through the first half of next week
(especially along the coast) as temperatures rebound closer to
seasonal normal values.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...CFW 155 161, NPW 181 185 195, WSW 155 161.
MARINE...Storms 150 155 165 170-171 179 180 181 185 412-414.
Gale 121 130-132 138 165 173-175 178 352 411.

&&

$$

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


551
FXAK67 PAJK 230705
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
1005 PM AKST Wed Nov 22 2017

.UPDATE...Precipitation type has again given us issues from Sitka
to Wrangell to Petersburg. Temperatures are way colder than
guidance for this region but guidance is indicating some warmer
air aloft that potentially could give us fits with freezing
liquid. However, calls to those communities including Kake reveal
none have reported a glaze tonight, just periodic wet snow, or
rain in the case of Sitka. Aside from the south central Panhandle,
we also made a quick early update to re- bottom temperatures a
bit lower given clearing skies near Haines and Skagway.

A new system will approach us on Thanksgiving Day. Initial lift
across the cold air dome will efficiently give us light snow
across much of the northern Panhandle, light rain for the south,
and a potential mix for the south-central areas as many feast with
friends, neighbors, and friends. We think snowfall amounts could
be around a couple of inches for much of the north-central
Panhandle including Juneau and Gustavus with lighter amounts due
to warming to the south and due to drier air to the north.

Thursday night, uncertainty rises among guidance solutions with
the amount of precipitation. Currently we favor the GFS and ECMWF
solutions, as both unite in positioning the low. Meanwhile, the
NAM seems to march too quickly toward shore. But of greatest
impact, is the NAM`s enhancement of precipitation around Juneau
during frontal passage late Thursday night (wee hours Friday
morning). While we acknowledge this could occur and therefore
necessitate greater snow amounts in our forecast than our 3
inches, many variables like warming and the angle of frontal
advancement--as it aligns almost east-west at that time--may
inhibit both QPF as well as the fluffy factor (ie, how dry the
snow is and how much it compacts, or does not, when it
accumulates). For these reasons, we feel the lighter QPF of the
ECMWF and GFS equating to around 3 inches of wetter snow
particularly toward morning is our highest confidence forecast at
this time. Please stay tuned. We have issued a special weather
statement to alert the public for this uncertainty, as confidence
is not there for a winter storm watch. We will continue to
monitor trends that can hopefully supply more answers rather than
raise more questions.

&&

.PREV DISCUSSION......ISSUED AT ...226 PM AKST WEDNESDAY

SHORT TERM.../Through Thursday night/ A weakening occluded front
over the central panhandle will dissipate by late tonight. Another
occluded front will move E into the central gulf Thu, then move NE
across the outer coast of SE AK Thu night. Other than some early
adjustments for this evening, did not make much change to the
overall forecast through Thu night.

One adjustment was to cancel the WWA for zone 25. The snow with
the occluded front has been on the meager side so far. While some
snow is still expected around the Juneau area this evening,
amounts will be less than 2 inches. Elsewhere, allowing the WWA
for zone 26 to expire at 4 PM this afternoon, as most of the
freezing rain threat should have ended by then.

Otherwise, precip should move out of the area tonight, but more
will move in for Thu and Thu night as next occluded front moves
in. There is also a shortwave trof preceding the front that will
bring precip to the area as well. Looking like it will be mostly
snow over the N third of the area, rain and snow over the central
third...and mainly rain over the S third. At this point, best
threat for WWA headlines will be in the N third of the area, but
confidence is not high enough to issue any attm. Currently keeping
snowfall amounts below advy levels for the N Thu and Thu night.

Northerly winds will pick up a bit over the N inner channels early
tonight, then drop off late tonight and Thu morning. They should
increase later The afternoon and evening. Looking like SCA level
winds at most for these areas. Also, SCA to gale force winds are
likely over the gulf Thu into Thu night ahead of the next occluded
front. Some of these stronger winds will get to the S inner
channels Thu night...with SCA level SE winds likely by then...as
occluded front moves onshore.

LONG TERM /Friday through Wednesday/ A weather front lying
across the Panhandle will support widespread precipitation Friday.
Temperatures across the central Panhandle will be marginally cold
enough for snow but confidence is only moderate. Even as warm air
lifts northward along the front, we think wet- bulb temperatures
should be lower than freezing. But given frontal orientation, we
are not considerate significant accumulations. Confidence is
higher for rain in the south. Very little changes were made in
winds during this time, as agreement continues to remain strong,
even as precipitation type is not as sure.

As the low pulls south, we are increasingly confident in a dry,
colder forecast. We lowered temperatures yet again for Saturday
and Sunday as outflow revs up again through the northern and
central Inner Channels. While currently we are only forecasting
gale force winds for northern Lynn Canal, it is conceivable these
may need to be expanded in coverage. We held back some of the
coldest air from some solutions as sky cover may continue to be
mainly cloudy due to a low to our southeast.

Leading into next week, we see some form of deeper onshore flow
returning along with a moderating temperature trend. This will
reintroduce precipitation type issues, but it is safe to say the
southern Panhandle and east and southeast gulf coast will return
to rain into the middle of the week while we forecasters continue
to debate and chase the ever impactful rain/snow line. As most
American students (and seasoned forecasters) will tell you, "When
in doubt, guess `C.`" Our "C" stands for Wrangell to Peril
Strait, and this supplies a reasonable first guess. Forecast
during this time period continues to more strongly rely on
ensembles as evolution back to a wetter pattern highlights the
creative differences of our solutions. For all of these reasons,
forecast confidence drops next week.

RWT/JWA


&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ012-013.
Small Craft Advisory due to Seas for PKZ041>043.

&&

$$

JWA

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