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000
FXAK69 PAFG 252143 CCA
AFDAFG

Northern Alaska Forecast Discussion...CORRECTED
National Weather Service Fairbanks AK
143 PM AKDT Wed Apr 25 2018

.DISCUSSION...

A active pattern across the state today that will most likely
continue through the weekend. Strong low pressure in the Bering
Sea continue to produce gusty winds to the west and in the Alaska
Range. It is also producing a mix of rain and snow showers from
Tanana west, and it looks like that will continue through the
weekend. There is some clearing in the Interior but expect some
showers to pop up around the area starting Thursday. Some fog
possible in the valleys as breakup continues and warmer air
persists over the snow.

Models...Have been doing a pretty good job with the short term.
Initialized against the surface analysis about 3 mb high, so winds
may be a couple knots higher that current solutions suggest. They
continue the timing struggle with the shortwaves that will be
moving through the area with no concensus. There is better
agreement on the front moving across the state on Saturday.

Aloft...at 500 hpa...Ridging Remains along 77N then southeast
across the Beaufort Sea, and southeast over central Yukon
Territory. A broad area of lower heights around a stacked 509 dam
low over Gambell covers the western 1/2 of mainland Alaska, the
Chukchi Sea, the Bering Sea, and south of the Aleutians over the
North Pacific. Several shortwaves will move north over the West
Coast the next 24 hours, while a stronger shortwave will move to
the Southwest Coast and Bristol Bay Thursday morning, and will lie
from Shishmaref to McGrath to the southern tip of Kodiak Island by
Thursday afternoon, then spits with the northern portion swinging
north to the Arctic Coast by Friday morning, and the southern half
moving south of the Alaska Range. A 516 dam low north of Kamchatka
will swing around the primary low to St Matthew Island Thursday
afternoon, then over the Lower Yukon Delta by Friday morning at
519 dam. As it gets caught up in the flow around the primary low
which remains quasi stationary in the Western Chukchi Sea it will
move into the Central Interior Friday night and troughing will lie
from Kivalina to Tanana to Skagway. The closed low merge with the
primary low by Saturday morning and the trough moves to lie from
Point Hope to Bettles to Eagle. Another wave will approach the
West Coast Friday night. At 850 hpa...Temperatures will remain in
the 0C to -10C range through Saturday. At 925 hpa...Still seeing
some 15 to 25 kt winds so gusts to 40 mph are still possible over
some of the interior summits into Thursday morning.

Surface...A 976 mb low over Gambell will drift north to the
Western Chukchi Sea by Thursday afternoon, and a 995 mb low will
spin out of Siberia to be over St Matthew Island. Troughing over
the Arctic Coast will persist, but weaken on Friday as high
pressure build south over the Eastern Arctic Coast. A bubble high
over the Interior will persist and merge with high pressure
building in from the south Thursday night with a ridging extending
from the high Arctic to the Gulf of Alaska over the AlCan Border.
The lows in the Chukchi Sea and and Eastern Bering Sea will merge
Friday and a 982 mb low will move to the Central Bering Sea at
984 mb, and to Nunivak Island by Saturday morning at 990 mb. The
low then moves north up the coast to the Seward Peninsula by
Saturday afternoon. In the Arctic a 1020 mb high will move south
over the Beaufort Sea Friday night and Saturday. Expect the
pressure gradient to tighten and relax several times through
Saturday with gusty winds developing as it tightens.

North Slope and Brooks Range...Front is working its way offshore
so expect clearing from west to east this evening if it has not
already. Some patchy fog developing overnight, mainly around
Deadhorse will reduce visibility in the morning. Winds swinging
around to east and southeast at 5 to 15 mph. Will remain nice for
through Friday over most of the area, even the Brooks Range which
may see some clouds, and some gusty winds at times.

West Coast and Western Interior...Not much change from yesterday!
Expect not quite as windy, but it will be cloudy, rainy, snowy,
and generally just kinda yucky to continue to the weekend. There
will be some periods of clearing, but for the most part they will
be short lived. Expect a mix of rain and snow depending on the
time of day with mainly snow in the overnight hours, except south
or Norton Sound it will be mainly rain, with rain mixing with snow
overnight. Snowfall amounts will vary widely, and locally. The
higher elevations in the Nulato Hills, Bendeleben mountains, and
Baird mountains will get 2 to 4 inches of new snow, with lesser
amounts at the lower elevations. Temperatures will be cooling
slowly as cold area wraps around the low.

Eastern and Central Interior...Mostly sunny to mostly cloudy. Some
isolated showers may pop up during the afternoons, mainly to the
west of Fairbanks. Expect some patchy fog to pop up as water
starts to slowly open up in the interior. Winds in the Alaska
Range continue to be gusty to 45 mph today, and will settle down a
bit tonight, but expect them to become gusty to 45 mph again
tomorrow as the pressure gradient across the range tightens up
again with leeside troughing redeveloping. No significant
precipitation is expected through Friday. Away from the range
winds will be variable to 10 mph in most areas. Temperatures will
remain springish with high around Fairbanks in the lower 50s, and
lows around 32 for most locations.

&&

Coastal Hazard Potential Days 3 and 4...Potential for some High
Surf around Scammon Bay and Cape Romanzof Friday afternoon and
evening.

&&

.Fire Weather...Near Red Flag conditions continue near the Alaska
Range. Winds continue to gust to around 50 mph this afternoon.
Gusty winds will continue through Thursday with gusts to 45 mph
near the Alaska Range. Winds will be strong and gusty at times
through the weekend. Relative Humidity values will fall through
Friday into the 20s, then rebound some on the weekend into the
30s. High temperatures in the 40s and 50s through the weekend.
Outside the Tanana Valley minimum Relative Humidity values
generally above 30 percent and winds in the valleys 5 to 15 mph.
There is slight chance of thunderstorm activity mainly west of
Fairbanks Thursday and Friday.

&&

Extended forecast for days 4 to 7...A low pressure system moving
across the Bering Sea will spread a mix of snow and rain to the
West Coast Friday night as it moves to the Lower Yukon Delta at
990 mb Saturday morning, and the Seward Peninsula Saturday
afternoon. This will bring showers to interior locations Saturday
afternoon through Sunday morning. Another fairly strong chinook
wind event across the Alaska Range brings south winds gusting 40
to 60 mph to the north slopes and adjacent areas. Expect
temperatures near seasonal normals across the forecast area. In
the Central Interior highs will be in the upper 40s to mid 50s,
with overnight lows around 32.

&&

.HYDROLOGY...Some of the interior river gages are coming online,
but most rivers remain frozen. For the gages available they should
be used with caution as they may be ice affected.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...

Small Craft Advisory for PKZ200-PKZ210.

Heavy Freezing Spray Warning for PKZ210.

Brisk Wind Advisory for PKZ215-PKZ220.

&&

$$

SDB APR 18


000
FXAK68 PAFC 260037
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
437 PM AKDT Wed Apr 25 2018

.ANALYSIS AND UPPER LEVELS...
A pool of cold air aloft from the nearly stationary low just south
of the Bering Strait continues to bring widespread rain and snow
showers as well as widespread clouds to much of the southern
Alaska Mainland. The most widespread shower activity has occurred
over the Northern Susitna Valley where persistent and moist
southwesterly flow has produced rain and snow since the front
passed through that area yesterday evening, allowing for about
4 inches of snowfall in the Cantwell area since yesterday
evening. Over the Southwest Mainland showers (mostly in the form
of snow) continue to move through the area and are beginning to
intensify with daytime heating. This may allow for the development
of a few isolated thunderstorms this evening (especially over
Eastern Bristol Bay). Conditions further west over the Bering
Sea/Aleutians are much quieter behind the upper level trough as
weak ridging is allowing for the development of stratus over the
Western Bering and diminishing winds.

&&

.MODEL DISCUSSION...
The models remain in great synoptic agreement through the work
week with the timing of a series of waves that will rotate around
the quasi-stationary upper low this week. Even with this good
agreement, there continue to be differences in the models in the
placement of shower activity as is often the case in these
southwesterly flow events. As a result, details in the precipitation
forecast into Friday focus on where there is agreement, such as
upslope prone areas of the Susitna Valley and Gulf Coast, with
widespread chance POP`s elsewhere. Looking into Friday, agreement
begins to improve significantly as a much deeper upper level low
moves through the Bering into the southern Mainland. This is where
much of the focus was for forecast updates today.

&&

.AVIATION...
PANC...Gusty south to southeasterly winds are expected to
continue into Thursday with little change the pressure gradients
along the Chugach. There will be a uptick in the winds this
evening, producing gusts to around 35 kt, which should then
fall to around 25 kt after sunset as daytime heating diminishes.
Otherwise conditions should remain mostly VFR as rain and show
showers pass through the area. Forecast confidence is however
low in the timing and track of these showers, so there is a
possibility that conditions may intermittently drop to MVFR if
heavier showers move through the vicinity of the airport. The
greatest risk of showers moving near the airport will be from
convective activity along the Chugach this afternoon/evening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Persistence will be a great forecast for the next couple days.
The driver will be the upper level long-wave trough, but more
importantly, the cold air contained within. There is a weak short-
wave moving up Cook Inlet tonight, which looks to focus convection
along the western Kenai Peninsula, keeping it out of the
Anchorage Bowl. However, it won`t be far away. These showers
should be mixed with rain and snow, possibly turning to all snow
in the Susitna Valley. Instability will be increasing as the cold
core aloft moves overhead tomorrow. Scattered rain showers will
increase in coverage during the afternoon, especially along the
higher terrain of the Chugach. These showers should be mostly
rain, but could see some rogue flakes or even graupel mixing down
to the surface in the more intense showers. The back edge of a
short-wave will pass late in the evening, bringing an end to the
showers, but the break will be short-lived.

A much stronger shortwave will be dropping out of the Bering
Strait region late Thursday evening. The effect will be first to
tighten the pressure gradient, returning stronger southeast gap
winds to Turnagain and Knik Arm, second to return rain and snow to
most areas. There is not any strong temperatures advection, either
warm or cold associated with this system, so precipitation type
should be strongly tied to the diurnal surface/low-level
temperatures. It likely will be rain during the day, mixed with
or changing to snow at night depending on location/elevation.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Cool and wet weather continue to plague Southwest Alaska through
the forecast period as an upper level low remains in place over
the Bering, and showery onshore flow persists over the area. A
series of waves will rotate around the base of the upper low
through Friday, bringing enhanced shower activity to the Bristol
Bay coast and up through the Kuskokwim River Valley. Models are
currently indicating these enhanced showers to line up over the
Bristol Bay area overnight tonight into Thursday morning, with the
next stronger wave tracking into the Southwest Mainland Thursday
night. There is potential for these showers to become more deeply
convective in nature as limited surface heating combined with cold
air aloft will lead to steep mid-level lapse rates and decent
instability through this evening. Guidance continues to show a
line of enhanced showers forming from a line between King Salmon,
Iliamna, and Sparrevohn through this evening. Thus, embedded
isolated thunderstorms may be possible in this area.

With the secondary system tracking in Thursday night, another
round of enhanced showers and gusty winds are expected to spread
from the southwest coast inland through Friday afternoon. Colder
air associated with this system as well as plenty of antecedent
cold air at the surface should keep precipitation as snow for most
locations, though expected accumulations remain minimal at this
time.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A broad upper low over the northeast Bering will remain stationary
through Thursday morning before shifting northward over the
Bering Strait by Thursday afternoon. Cool and showery conditions
over the eastern half of the Bering/Aleutians are expected to
persist through Thursday afternoon, under gusty westerly flow.
Whereas over the western half of the area, shortwave ridging
begins to build over the area tonight, bringing drier conditions
to the western/central Aleutians through Thursday afternoon. With
the shortwave trough dropping southward over the eastern Bering
Thursday, we are expecting colder temperatures and snow showers
to persist over the area through Thursday night.

By Thursday evening the next system enters the western
Bering/Aleutians, and tracks eastward through much of the Bering
and Aleutians by Friday night. This system will spread gale force
winds and rain along much of the chain, as it pulls warmer Pacific
air northward and tracks eastward across the Aleutian chain
through Friday night.

&&

.LONG TERM FORECAST (Days 3 through 7)...
A system over Southeast Alaska Friday evening will quickly move
east and dissipate Friday night. A fairly significant upper low
will be over the central/eastern Bering Friday night. The leading
front will push across Southwest Alaska early Saturday morning
and then into the Gulf and Southcentral during the day Saturday.
The upper level low will move eastward across the Gulf Saturday
night. A fairly strong surface low will move into the Bering on
Saturday. After this, the model guidance begins to diverge. The
models agree on continued fast zonal flow aloft, along with the
general idea of an upper low in the Bering and upper ridging over
the northeast Pacific into eastern Alaska. However, the location
and timing of various systems has a large spread in the guidance.
Therefore the fairly active weather pattern will continue, with
the details not well defined. Thus, the WPC guidance begins to
lean fairly heavily on the ensemble means after Monday.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale Warning 175 176 177 178.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...DEK
SOUTHCENTRAL ALASKA...MTL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...BL


000
FXAK67 PAJK 252205
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
205 PM AKDT Wed Apr 25 2018

.SHORT TERM...Large upper low continues to spin late this
afternoon over the Bering Sea while upper ridging is building
along the BC coast. Between these two systems is the remnants of
the front that brought 1.5 to 2 inches of rain to the Yakutat area
last night. This front is little more than a weak surface trough
but SW flow aloft continues to advect a narrow stream of moisture
over the northern/central Panhandle as evidenced by PW values
around 1 inch on GOES blended PW imagery. Southern areas have seen
partly to mostly sunny skies today with temperatures warming into
the mid 50s while the corridor from Sitka to Gustavus/Juneau as
seen chilly light rain with temperatures in the mid 40s.

Guidance indicates that the mid/upper ridge will continue to build
through Thursday. This will prevent the weak surface front from
advancing any further south. Instead, one or two weak waves will
run along the front through Thursday morning, keeping light
precipitation going through mid day Thursday in roughly the same
area as today. The front will eventually weaken and dissipate by
Thursday night as surface ridging begins to develop over the Gulf.
With continued weak onshore flow in the 925 to 850 mb layer
through Thursday, going to be hard to scour out the low level
moisture. Even Thursday night, as the flow turns NW`ly, while we
may dry out, clouds will likely hang around especially along the
coast and the northern/central Panhandle.

SW winds are currently gusting to 40 mph in the Skagway area with
25 kt southerly winds in N Lynn Canal. As the stronger SW flow
aloft diminishes this evening, expect these winds to diminish. By
Thursday morning, light winds are expected in most areas as the
gradient goes to almost nil. Kept 15 kt southerlies in Lynn Canal
Thursday afternoon due to thermal gradient but otherwise winds
should become more NW`ly by thursday night as surface ridging
builds over the Gulf.

Overall models are in good agreement and forecast confidence is
above average.

.LONG TERM.../Friday through Wednesday/...A large surface high
will be centered south of the Aleutians at the start of this long
range forecast period. Prominent ridge axis extends northeast
diagonally across the gulf. Farther north, a low near the Bering
Strait will be pushing a front east across the southern portion of
the state and along the northern periphery of the surface ridge.
Models are currently in significantly better agreement with this
set-up and changes were made in the extended forecast to reflect
this. Main change has been to increase the likelihood of rain from
Friday onward. The front referenced above will not make much
eastward progress beyond Cape Fairweather. However, a second
frontal feature will cross the central gulf beginning Saturday and
arrive along the central/southern outer coast by Sunday morning.
A third front will cross the gulf on Sunday and spread rain across
all of the panhandle Sunday night.

With the increases to PoP and based on model spectrum spreads,
decided to diminish daytime highs slightly. Overnight lows were
adjusted up even less. Net effect will be a diminished diurnal
range over the coming week.

Blended GFS, ECMWF, and the Canadian NH for pressure through
Sunday night. Used Canadian NH winds as a foundation through
Friday night, then primarily GFS. Preferred the SREF PoP field
early on, but then favored the upper level pattern depicted in GFS
for the second and third fronts and how they interact with the
surface ridge.

Forecast confidence in a continued wet pattern for the upcoming
week remains lower than average but is increasing.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind until 4 PM AKDT this afternoon for AKZ018.
Strong Wind from 6 PM to 10 PM AKDT this evening for AKZ018.
MARINE...Small Craft Advisory for PKZ012.
Small Craft Advisory due to Seas for PKZ022-041>043-051>053.

&&

$$

DEL/Fritsch

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